韩国经典三级

韩国经典三级In the World of the High Tech Redneck, the Graybeard is the old guy who earned his gray by making all the mistakes, and tries to keep the young 'uns from repeating them.Silicon Graybeard is my term for an old hardware engineer; a circuit designer.The focus of this blog is on doing things, from radio to home machine shops and making all kinds of things, along with comments from a retired radio engineer running from tech, science or space news to economics; from firearms to world events.

Saturday, June 27, 2020

A Ham Radio Series 6 – Choosing an Antenna

So far in this series, I’ve mostly talked about HF and low VHF propagation and some antenna overview topics.  My slightly snarky three laws of antennas have truth embedded in them.  If you don't have an antenna anything you put up will get you contacts.  There's a group of hams who try to operate with the lowest power or most meager antennas they can and sometimes with both low power and "compromise" antennas at the same time!  They measure miles per watt for bragging rights.  1000 miles per watt will get you a certificate suitable for framing, and the records are many times that.
The current QRP miles per watt record is 1,650 miles from Oregon to Alaska on the 10-meter band using 1 microwatt! That’s the equivalent of 1.6 billion miles per watt.
The second law was that nothing is best at everything, and it's pretty common to want to upgrade your antennas.  A saying that I agree with more almost every year is that if you suddenly got a windfall chunk of change and really wanted to upgrade your station, look at your antennas first.  

For the past several months, I’ve been looking at antennas I can put on my suburban lot that would give me better coverage on two different bands, and I thought some of you might be interested in what I’ve been doing to evaluate options.  For this post, I’m going to talk about the amateur allocation on 30 meters; or 10.100 to 10.150 MHz.

For antenna work, if you go with a resonant, full-sized antenna, there are a couple of formulas you need to know.  For a half-wave dipole, the length in feet for a half-wave at a frequency (f) in MHz is given by:
L = 468 / f
Since a monopole is one half of a dipole (one pole is half of two poles), it’s length is half of the dipole's or L = 234 / f. 
For the middle of the band, that tells me a half-wave dipole is 468/10.125 or 46.22 feet (that’s 46 ft 2.6 inches).  A monopole is 23 ft 1.3 inches.

Which one do I use?  As always, the answer is “it depends;” in this case it depends on what I want it for.  My preference for this antenna, as with all of my antennas, is for distant contacts.  That means I want a low angle of radiation.  Which antenna should I try to put up?

Let me stop here for a moment.  Why is there a choice between one or two “poles” and what does that even mean?  A half-wave dipole antenna has a length that closely matches the physical length of the radio waves.  As mentioned in the Antennas 101 Part 1, the voltage and current physically fit on the dipole like this.  Current is zero at the ends because there’s no where for the moving electrons to go.  Voltage is high were current is low because the power (voltage times current) is constant.


To show that conceptually for a monopole, you cut it in half at the middle, and rotate it so that it’s vertical.   Here, I cut off the right half and the left half is now vertical.


This antenna works because there’s a virtual second monopole; a reflection of the top monopole in the ground making it a virtual dipole.  In reality, if you’re mounting a monopole vertically like this, you need a better ground than most people get out of their actual ground.  AM broadcasters do this by burying a radial array of wires centered under the vertical.  In practice, four quarter wave long wires arranged radially just below the grass is pretty common.  Note that this sometimes called a ground plane antenna although usually just called a vertical.  If you live on a saltwater marsh (really, any body of water) you're good to go without putting down radial wires.

I’ve simulated several antennas in EZNEC 6 (freebie equivalent), and have some comparison plots.  First off, here’s a 30m dipole situated 20 feet above ground, so just under ¼ wave up.  This is an Elevation plot, that shows which direction the signal is strongest, marked from horizontal to vertical.  The farther out the red trace is, the stronger the signal is.  The antenna is conceptually at the bottom where everything converges, and you’re looking at one end of the wire sticking out of the screen at you. 


Notice that the strongest signal is going straight up.  The performance at 45 degrees from the ground isn’t that bad, it’s only down a little over 1 dB, but I can move a marker on the plot and find that the half power point, -3dB, is at 32 degrees elevation.  This dipole will be better for local contacts than those distant stations.  Very little power radiates at low takeoff angles.

Given that, let’s see how the vertical compares.


Because of the way EZNEC presents this data, I drew in a green line to represent the ground.  The radiation is strongest right along the ground.  This is close to ideal for those distant, DX stations I want to work.

There’s a gotcha.  Notice the gain figure on the right in both plots.  The dipole has more gain than the vertical but a worse pattern.  Even with the lower gain, the vertical puts more power into take off angles below 20 degrees than the dipole does.

To get a lower radiation angle from the dipole you need to put it up higher.  A half wave is better than a quarter wave. This is the same antenna when it’s 46’ up instead of 20.  Not many people have the real estate to support both ends of a 46' long dipole held 46' up in the air by two towers. 


I should point out something important.  All antenna modeling programs present impressive results that won’t match reality exactly because the world is much more complicated than the models.  The only thing in the universe of these models is what you model.  There are no buildings, no metal roofs, no towers, no cars parked across the street, nothing.  What that means is that this is an indication of performance, not an absolute model of what you’ll get.  The world around the antennas makes the patterns lumpy and asymmetrical.  The patterns are distorted, but reality resembles the model. 

You might ask if an electrically shortened antenna using loading coils or traps (parallel resonant circuits) effects gain.  It affects signal radiated but not the pattern so much and not by large amounts.  If you use an antenna tuner and a random length of wire, as many people do, you will lose power and received signal in the tuner.  If it gets you on the air and gets you contacts, you can worry over every milliwatt you might lose, but remember the ionosphere isn't constant and power levels flicker all the time, too.  My personal take on it is not to worry about loss in the tuner if the ionosphere takes out six or seven dB in a flicker.   If the radio's happy, I'm happy. 

Which way am I going for my 30m antenna?  I'm not really done with trying options, which is more about looking at my lot than running simulations.  My current antenna is a commercially made electrically short (trapped) vertical for 80 and 40 meters.  It's electrically long on 30m, and tuned with the radio's antenna tuner.  I've been using it on 30m since I got it in 2008, so it works, I just would like better.  Without dropping large sums of money on it. 



Friday, June 26, 2020

The Continuing Chronicle of the Cam, CNC and CAM

My last shop update post, a week ago, mentioned that one my next parts for my Webster engine was to be the exhaust cam.  I mentioned that the plans I'm using recommend using a method developed by a model engine designer named Hamilton Upshur, which requires building a fixture to turn the cam eccentrically.  It wouldn't work to just turn it off center with a four-jaw chuck because the cam gets rotated a bunch of times and just a little metal taken off.  This fixture is turning it off center twice.  This is interrupted cutting; it only cuts for a few degrees of rotation so the lathe has to not shake itself apart while doing this.

Last Saturday I finished the fixture:


Right below the socket head cap screw is a 1/2" diameter washer.  The next thing down is the cam blank: turned on the lathe to an Outside Diameter of 0.712" and the Inside Diameter reamed to 0.375".  Lacking solid step by step directions, I realized I needed to turn this on the outer diameter until I could verify that the bottom would be the right thickness; the OD minus ID of 0.094".  I just didn't see quite how to get from that first step to a complete cam.  As a result, my cam came out with a cam-like shape (or egg-like), but any outside dimensions that matched were purely a coincidence.


After posting my picture to the Home Model Engine Machinist forum, one of the wizards sent me a pdf he had previously posted of how to cut these.  The biggest mistake I made was starting from the center and trying to work to some lines I had scratched on the blank (coated with blue Dykem), then flipping it over and going back to the bottom center and trying to do the same thing going the other way.  The way to do this is to start at some point, and then rotate the blank 5 degrees at a time until it starts to look like a cam and then measure the top of the cam and stop when you get to the desired width.  For this cam, that's 43 steps.  For each step, I unscrew that cap screw, rotate the blank 5 degrees (where the tool is cutting, that's about .024"), tighten the screw and turn it again.  This time it came out much better.


You can see it's less lumpy, and in fact better than the first in just about every measurement.  The problem is that the bottom 3/4 of the cam is too thick.  Instead of 0.094", it was 0.125".  So back to the fixture to try to resize the rest of the cam.  That failed - one time when I tightened the screw down I guess I didn't tighten it enough and it slipped.  The top section of the cam got undersized by almost 1/16". 

Now what?  Do I proceed to cut a blank and do this again, or like an anonymous comment said to the last post,
Cam looks like a job for the cnc mill to me.Bolt the blank down to the table, through the hole, on top of a sacrificial piece of aluminum.
I was interested in doing it with this fixture for two reasons:  first, to be honest, just to do it manually (which is because) second, the guys on that forum seem to be completing their projects at least a thousand times faster than I do.  That implies CNC is holding me back.

It just seems that if CNC is holding me back, and if CNC is a strong feature of my shop (maybe the strongest) maybe I should be trying to get better at CNC programming.  So instead of using my CAM program (Computer Aided Manufacturing) to create the tool paths to make the cam, which has a simple outline, maybe I should write the program by hand.

I started out like this:


Each of the turquoise colored circles is the end profile of a 3/8" diameter end mill.  The centers of the four at the top are listed in the lower right.  The tool path is to start at number 1, move in a straight line to position 2, then do a section of a circle that takes the cutter to 3.  From there, do a straight line to 4 and then straight to 1. The gold outline is the cam drawing, and the almost white circle is the blank.   For some reason I don't understand (but that I had read could happen) the Mach3 interpreter didn't understand my code to go from 2 to 3 and almost went straight across.  After troubleshooting for a while, I thought I'd add that unnumbered position at the middle bottom, cutting the arc motion into two movements.  After that, the test cuts (air cuts) looked perfect and I cut this. I cut this in .031" thick slices, from top to bottom, making the entire file six copies of this with one modification (the first line goes .031 deeper each pass):
G01 X0.220 Y0.828
G01 Z-0.031 F2
G01 X0.427 Y0.476 F5
G02 X0.000 Y-0.188 R0.470
G02 X-0.427 Y0.476 R0.470
G01 X-0.220 Y0.828
G01 X0.220 Y0.828
This file is 42 lines long because of the two G02 (cut an arc clockwise) commands.  The file my CAM program made, which is entirely small steps from one point it chose along the side of the cam the next point it chose instead of G02 statements, is over 10 times as long.

Here are all three cams with the CAD/CAM/CNC cam on the right.   This is right off the fixture with the barest amount of deburring.


Clearly, I would have wasted less metal and been done faster if I hadn't spent a few days trying to turn it on the lathe fixture.  The question is whether or not sitting down to make the cam with CNC from the start would have gotten me done faster than if I knew how to do it with the fixture in the lathe. I think the answer is yes. 

The reason why some of the wizards on the HMEM have done three engines since the first of this year and I've been working on this one for over a year is that for me, just about every part is the first of a kind and I've never made one before.  My second cam is virtually guaranteed to go faster than this one.  I don't know enough about engines to really see how this goes together so I spend too much time thinking about most parts.  If someone wants to make model engines, they'd probably be better off working on small engines and antique farm engines than learning how setup a CNC mill and lathe. 



Wednesday, June 24, 2020

Yesterday's SpaceX Tank Popping Was Deliberate

For the second time, SpaceX Starship test article Serial Number 7 was tested until the new steel structure failed.  This was a deliberate test to failure, unlike the first test nine days ago, which just popped a leak. 


That's a screen capture from this NASASpaceflight.com video.  A look at the wreckage from up close later in the day shows that the bottom of the tank blew out pretty extensively.  You can see the tank and test stand lift off and fly to the left in the video (and in that picture above).  The two dark objects sticking out of the highest spot in the white cloud is a pair of valves that were releasing LN2 vapor.  The test consisted of closing those valve and then monitoring the pressure build up until the tank blew.  This was deliberately destructive test to see what fails and at what pressures.


There is no SpaceX data release telling us how well the tank performed.  The working pressure that tanks have been tested to is about 125 pounds per square inch (PSI), which is a 40% safety margin over the worst anticipated flight conditions, but those are not intended to be destructive tests.  Whether or not the tank survives that pressure for some time is the criteria.  This is more a test of everything, the sheet steel, the processes, and their understanding of all of those. 

The destructive test was yesterday around lunch time; I missed the failure but had kept the tab open in my browser.  When I went back the tank didn't look as good as the second picture and I rewound the video to see the pop.  Early this morning, the full sized test vehicle SN5 was rolled out to the test stand and mounted on the stand while the remains of SN7 were being cleaned up.   There don't appear to be any road closures for another several days, which indicates no testing at least until then.  The next road closures are for Jun 29th through July 1st.  I've watched the channel enough to know those dates are extremely fluid.

Meanwhile the third Starlink mission in as many weeks is scheduled for tomorrow at 1639 EDT, 4:39 PM.  This has slipped a couple of times, with no explanation I can see.  Like the last mission, this will be a ride share flight, and a couple of Starlink satellites will be pushed off to a later mission to accommodate the first two BlackSky satellites from Washington startup LeoStella.  Those ride sharing photographic satellites are believed to weigh around 55 kg (~120 lb) each.  The booster for this flight is B1051 and is scheduled to become the third SpaceX rocket to launch five times when it lifts off.  Only one has successfully landed and been recovered; B1049 from the first Starlink mission of this month is in the inspection and refurbishment process now.   



Tuesday, June 23, 2020

Got Time for a Podcast?

To follow on to Bayou Renaissance Man's post about blogger Small Dead Animals.

Go to Glenn Beck Program Podcasts and at the top of the page click on Hourly.  This only holds the last few days; look for hour 2 of today, 6/23/20.  After stumbling around for a half hour, I found a link to embed here so that you can get it for the foreseeable future.  Once the audio starts it's worth skipping ahead to about the 5 minute mark to avoid some commercials (just click on a faux audio plot; the timer is on the right - or drag the slider across on the bottom of the linked page).  The part I want to direct you to is the first "half hour" of the radio show.  The podcast is all the content in an hour of broadcast radio, so the whole thing is 41 minutes long and the interview ends at about 23 minutes on the timer.  That means you have 18 minutes to listen to.

The topic is the Great Reset, a Top-down-driven, Crony Socialist Revolution that we seem to be living in the early days of.  The Small Dead Animals post leads into this.  The big picture idea is to crash the dollar as the world's reserve currency and completely wipe out the world's economy then replace it with a crony socialist system.  I get a couple of financial/economic email newsletters and they have been talking about the economic situation that's central to the story (sample here from Bill Bonner). 
In an article published on the World Economic Forum’s website, WEF founder and Executive Chairman Klaus Schwab said “the world must act jointly and swiftly to revamp all aspects of our societies and economies, from education to social contracts and working conditions.”

“Every country, from the United States to China, must participate, and every industry, from oil and gas to tech, must be transformed,” Schwab added. “In short, we need a ‘Great Reset’ of capitalism.”

Sharan Burrow, the general secretary of the International Trade Union Confederation (ITUC), said we need to use the present crisis to help “rebalance” the global economy.

“We need to design policies to align with investment in people and the environment,” Burrow said. “But above all, the longer-term perspective is about rebalancing economies.”

And they weren’t alone. Numerous other influential world leaders spoke at the WEF event, including Ma Jun, the chairman of the Green Finance Committee at the China Society for Finance and Banking and a member of the Monetary Policy Committee of the People’s Bank of China; Bradford Smith, president of Microsoft; and Gina Gopinath, the chief economist at the International Monetary Fund.

Specifics for the plan have yet to be laid out. Those will come at WEF’s meeting in Davos in January 2021, the theme of which will also be “The Great Reset.” But, like the Green New Deal, it’s clear that the purpose of the plan—as the quotes previously listed reveal—is to move the world economy toward socialism, using climate change and COVID-19 as justifications.
The podcast is an interview with Justin Haskins, whose "about the author" box reads:
Justin Haskins is editor-in-chief of StoppingSocialism.com. Haskins is a widely published writer and political commentator, the senior editor and founder of The Henry Dearborn Institute for Liberty, and the editorial director and research fellow at The Heartland Institute, a national free-market think tank. Follow him on Twitter @JustinTHaskins.
Offered for your consideration.



Monday, June 22, 2020

The Roman Famine of 44 BCE and an Alaskan Volcano

Those of you familiar with Roman history around the time of the assassination of Julius Caesar know that event led to a couple of decades of turmoil and civil war that marked the transition from Republic to Empire.  History records that there was also a widespread famine due to crop failures in the same period.

A research team recognized the similarity to more recent volcanic eruptions causing cold growing seasons and failed crops, and started trying to determine if there was a volcano eruption that could be linked to this famine.  They found a likely culprit half a world away in Alaska.
Around the time of Julius Caesar's death in 44 BCE, written sources describe a period of unusually , , famine, disease, and unrest in the Mediterranean Region -impacts that ultimately contributed to the downfall of the Roman Republic and Ptolemaic Kingdom of Egypt. Historians have long suspected a volcano to be the cause, but have been unable to pinpoint where or when such an eruption had occurred, or how severe it was.

In a new study published this week in Proceedings of the National Academy of Sciences (PNAS), a research team led by Joe McConnell, Ph.D. of the Desert Research Institute in Reno, Nev. uses an analysis of tephra (volcanic ash) found in Arctic ice cores to link the period of unexplained extreme climate in the Mediterranean with the caldera-forming eruption of Alaska's Okmok volcano in 43 BCE.

"To find evidence that a volcano on other side of the earth erupted and effectively contributed to the demise of the Romans and the Egyptians and the rise of the Roman Empire is fascinating," McConnell said. "It certainly shows how interconnected the world was even 2,000 years ago."
The discovery was initially made in a lab last year when McConnell and Swiss researcher Michael Sigl, Ph.D. from the Oeschger Centre for Climate Change Research at the University of Bern happened upon an unusually well preserved layer of tephra in an ice core sample and decided to investigate.  With this strong lead, the researchers looked for corroborating evidence on ice cores from Greenland and Russia, some of which were drilled in the 1990s and archived around the world.  What they found was evidence for two distinct eruptions—a powerful but short-lived, relatively localized event in early 45 BCE, and a much larger and more widespread event in early 43 BCE with volcanic fallout that lasted more than two years in all the ice core records.
The researchers then conducted a geochemical analysis of the tephra samples from the second eruption found in the ice, matching the tiny shards with those of the Okmok II eruption in Alaska—one of the largest eruptions of the past 2,500 years.

"The tephra match doesn't get any better," said tephra specialist Gill Plunkett, Ph.D. from Queen's University Belfast. "We compared the chemical fingerprint of the tephra found in the ice with tephra from volcanoes thought to have erupted about that time and it was very clear that the source of the 43 BCE fallout in the ice was the Okmok II eruption."
How bad was it?
According to their findings, the two years following the Okmok II eruption were some of the coldest in the Northern Hemisphere in the past 2,500 years, and the decade that followed was the fourth coldest. Climate models suggest that seasonally averaged temperatures may have been as much as 7oC (13oF) below normal during the summer and autumn that followed the 43 BCE eruption of Okmok, with summer precipitation of 50 to 120 percent above normal throughout Southern Europe, and autumn precipitation reaching as high as 400 percent of normal.
All from a volcano half a world away, reminiscent of the year without a summer in 1816 caused by Mt. Tambora in Indonesia; a year known as "1800 and froze to death" in Vermont and New England.


Alaska's Umnak Island in the Aleutians showing the huge, 10-km wide caldera (upper right) largely created by the 43 BCE Okmok II eruption at the dawn of the Roman Empire. Landsat-8 Operational Land Imager image from May 3, 2014. Credit: U.S. Geological Survey

It's worth noting that the eruption and the famines led to the end of the Ptolemaic Kingdom in Egypt as well as contributing to the end of the Roman Republic and ushering in the Roman Empire.  The ruler of the Egypt was Cleopatra, so in one post we get Cleopatra, Julius Caesar and Mark Antony (related).   I also have to say that while it's published on Phys.org, which is a site for popularizing science research, that they talked about the affects to the climate.  No, a volcanic winter is no more a climate event than a nuclear winter.  It's a weather pattern.  If it doesn't last at least 30 years, and more like 50 years, it's weather not climate.

 

Sunday, June 21, 2020

What If I Trust Science, But Don't Trust Big Government Science!

If you pay any attention at all to the drivel coming from the leftist media (the vast majority of media) you'll have heard the idea that anyone who questions anything from authority is a "science denier."  That's an awful term, crafted to create a subconscious link to holocaust deniers.

This has been rumbling in my mind a lot, but credit (blame?) PJ Media author Stacey Lennox for bringing it into focus today with her piece, "What If I Trust Science and Don't Trust Dr. Fauci?"  Her emphasis is on Dr. Fauci and the Kung Flu crisis, but it's broader than that.  Let me go with a few of her points for a while.

To begin with, she quotes Dr. Fauci himself from a US Department of Health and Human services podcast saying:
“One of the problems we face in the United States is that unfortunately, there is a combination of an anti-science bias that people are — for reasons that sometimes are … inconceivable and not understandable, they just don’t believe science, and they don’t believe authority,”
The problem is that this week, the same Dr. Fauci admitted that he lied to Americans about the effectiveness of masks. They decided to tell us masks didn’t work rather than tells us they were effective in preventing the spread, but please refrain from buying them until we have an adequate supply for healthcare workers.  Personally, I believe if they had simply said, "if you buy up all the masks and healthcare workers don't have them, we'll have to abandon hospitals because workers are required by law to wear them" that people would have been understanding and bought up fewer masks.

It's a lot easier to trust people who don't have a documented history of lying to you.  Could that be part of it Dr. Fauci?

Another topic that doesn't make sense and leaves me with Looney Tunes-style question marks in the air over my head is why is an old, well-known drug that was showing promise against the disease so politically divided?  The easy answer is that a couple of conservative commentators started talking about success with Hydroxychloroquine and then the president started talking it up.  Suddenly, liberal commentators couldn't acknowledge they might be right.  Dr. Fauci joined the liberal pundits against the drug.  Ms. Lennox (a Registered Nurse) says:
The debate over this generic drug that has been in use for decades is one of the most puzzling and ridiculous things about the entire pandemic. The medicine was politicized and became controversial. After researching it myself and listening to practicing physicians who were using it, I expected Dr. Fauci to step up and clarify why there was a reason to believe it may work in conjunction with the mineral zinc. He never did.

I found this odd since the drug’s older cousin, chloroquine had been demonstrated to inhibit the SARS virus, which has a 90% overlap with COVID-19. The NIH did this study in 2005, where Dr. Fauci is a director.
We report, however, that chloroquine has strong antiviral effects on SARS-CoV infection of primate cells. These inhibitory effects are observed when the cells are treated with the drug either before or after exposure to the virus, suggesting both prophylactic and therapeutic advantage.
Any doctor that was recommending the treatment recommended it be given with zinc. The properties of zinc on RNA viruses, which COVID-19 is, are also well known. Again a study from the NIH in 2010 shows that with a companion ionophore, or drug that allows more zinc to enter the cell, the mineral interferes with the replication of the virus. Both chloroquine and hydroxychloroquine are zinc ionophores.
When people see contradictory messages, they try to understand why one group of doctors currently treating patients with these combinations and reporting excellent success gets no press or negative press, while another group of doctors saying it's poisonous and will kill people gets all the media attention.  As result, people try to think of reasons and decades of experience with government at all levels brings thoughts of corruption to mind.  I really doubt that I'm the only guy who has heard people saying Dr. Fauci and the Anointed Health Experts must be in the pocket of Big Pharma.  After all, they argue, why use a very old, cheap, generic drug when there are newer, more expensive drugs, like Remdesivir that can be sold?   Why should they allow drugs that cost a couple of bucks per dose when there are drugs that cost a hundred or hundreds of bucks per dose? 

Again, it's easier to distrust people who have lied to you before.

Stacey Lennox's article contains more good information related to the virus crisis, but if you take the same thoughts and expand them to wherever government big Science! is involved, you get similar answers.  The easy one to cite is climate change.  The trillions of dollars at stake have attracted the grifters that humongous sums of money always attract and every claim has to be carefully examined. 

Another example is the USDA Dietary Guidelines.  The science behind the USDA recommendations is atrociously terrible - the King of Junk Food Science is an example of the kinds of stuff they're based on.  Part of that is because it's both ferociously hard and expensive to do the kind of experiments that can give the answers people want.  While, saying, "it's too hard" is a hell of a poor thing to say, it's better that they're honest about how tenuous their data is.  The committees drafting the 2020 Guidelines have been meeting this year and they've been more (apparently) corrupt than ever, prompting federal Whistle Blowers to come forward and report bad behavior on the part of the subcommittees involved. Full disclosure: I've donated to the Nutrition Coalition and think that their work is good.

It would be better for the USDA guidelines to be shut down and the government to get out of the business of telling people what to eat, but right now that would require many laws or regulations to be revoked because the dietary guidelines influence military meals, school lunch (and breakfast) programs, hospitals, nursing homes and all sorts of institutional programs that feed people.  

Real science is a rigorous process for learning.  It's never preaching from a standpoint of "I'm all-knowing" and it's never "settled" except in the rare cases of physical law and one way you can be sure it's settled is that nobody is doing research into a field.  Nobody disputes that gravity exists; there might be research into fine details of the subject, but the fact that gravity exists is settled.

In the case of a new disease, nobody can be expected to know enough about it when it first appears.  It was quickly apparent that the doctors on front lines treating patients knew far more about it than the Experts.  Consequently, if people don't flock in admiration to the Anointed Experts, it's not that people have "an anti-science bias," it's that they know they've been lied to before or that their life's experiences tells them something funny is going on.  You see, Dr. Fauci, it's not "anti-science bias" to question things.  Questioning things is the essence of science.  Just accepting things the scientists say is the essence of religion. 


Dr. Fauci and Vice President Pence, April 19 Covid-19 press conference.  (AP Photo/Andrew Harnik)



Saturday, June 20, 2020

A Ham Radio Series 5 - Antenna Polarization

One of those questions that comes up from time to time is from someone who has heard antennas are polarized and wants to know if that matters.  The answer, as always, is that it depends. 

The polarization of the radio waves from an antenna is ordinarily given as the polarization of the electric fields.  As a recap, a radio wave is an electromagnetic wave, like ordinary light but lower in energy.  In the 1800s, you may recall from reading or a class at some time, it was thought that light propagated in a medium called the Luminiferous Aether because there was ample evidence light traveled in waves and how can there be waves that aren't waves of something.  Without spending too much time here, the presence of the Aether was disproved by the Michelson-Morley experiment and then finally buried by early 20th century advances.  Long before that, Maxwell described how an electromagnetic field can propagate forward as a changing electric field created a changing magnetic field which created a changing electric field ... repeating forever. 

(source)

Animation of EM wave propagation; by convention the electric field is called E while the magnetic field is B.  The important part to notice here is that both fields maintain the same orientation as they propagate.  

The general rule is that horizontal antennas produce horizontally polarized radio waves while vertical antennas produce vertically polarized antennas.

Why do we care?  Anytime radio propagation is local or line of sight, the polarization will be maintained and various radio services have established preferences for polarization.  An antenna set for one polarization rejects the other.  The theoretical attenuation on a cross polarized signal, like a horizontally polarized signal on a vertical antenna, is infinite.  You never get truly infinite rejection because that depends on the antennas being perfectly perpendicular to each other, and very small angular differences matter.  A cheap and dirty workaround, although you lose signal compared to antennas in alignment, is to rotate one antenna 45 degrees to the vertical.  This loses 3 dB compared to perfect alignment, but is an easy workaround if you were to be unsure of how signals would arrive at your antenna, vertically or horizontally polarized. 

Virtually any service that uses vehicle mounted antennas or handheld radios is based on vertically polarized signals - taxis, police, fire, emergency medical, and ham radio FM services (most popularly the 2m or 440 MHz handhelds or car mounted radios) come to mind.  I know of no exceptions.  While vertical polarization is the default on the 2m repeaters, if you drop down to 144.200 and switch over single sideband, the default there is horizontal polarization.  A few times over the years, I've heard guys just getting started on sideband using their vertical 2m FM antennas and being disappointed until they rotate the antenna. 

If the propagation is ionospheric, the polarization gets "scrambled "in the ionosphere by a phenomenon called Faraday rotation.  This goes for your attempts at working the other side of the world or the guy behind the next hill by sending your signal straight up.  If you're using a vertical to work some remote island and they're using a horizontally polarized beam (or dipoles) polarization doesn't matter. 

Horizontal and vertical polarization are just the basics, there are other kinds.  Circular polarization, (the general case is elliptical polarization) is a natural phenomenon - see the previous link on Faraday rotation - and is commonly used in some satellite downlinks.  Quadrafilar helix or turnstile antennas are common amateur approaches to receiving weather satellites.  The tricky part here is that there are two types of circular polarization, too: Right Hand and Left Hand Circular Polarization (RHCP and LHCP).  Those antennas reject the other polarization and I don't know of a trick like mounting the vertical or horizontal antenna at 45 degrees. 

If you're interested in HF, polarization is less important than the antenna pattern you get from either a horizontal or vertical antenna.  The effect of antenna height is talked about in this post from February of 2018.  


The same 40 meter dipole mounted at 66' above ground (left) and one foot above ground (right).  On the left it's a respectable pattern for long distance contacts.  On the right, it's an NVIS (Near Vertical Incidence Skywave) for local contacts.  Vertical antennas tend to have low angles of radiation, like the dipole at 66' but with even lower take off angles. 



Friday, June 19, 2020

Shop Update

It has been almost three weeks since I posted an update.  I ended up spending more time than usual in the ham shack instead of the metal shop last week.  The parts I'm working on are either small or fiddly or both.  Let me show you some of what I've been up to.


The top piece is the simplest, but still a fiddly bit.  It's a washer made from brass rod that's 1/4" OD with a 1/8" hole down the center.  It's easy to do this; the only touchy operation is cutting off a .015" thick sliver of a brass rod with a 1/8" hole down its center.  The cutoff tool usually leaves a nib that has to be trimmed off and then the whole thing needed to be lapped on sandpaper to bring the thickness down about .003".  I could make washers like this and sell them, but one of these would cost you the same as a box of 1000 stock washers.  It's kind of silly to make things like this.

The piece of bar at lower left is straightforward cut a piece of 1/4" drill rod to 0.938" long and then move it to the mill (or good drill press) to drill a 1/16" cross hole through it 0.844" from one end. 

The piece at the lower right is the blank for the cam pictured just to its left.  I've never made a cam like this and there's a couple of ways to make them.  The plans I'm using recommend using a method developed by a guy named Hamilton Upshur, which requires building a fixture to turn the cam eccentrically - that is, off the centerline of that big 3/8" reamed hole in the center.   I had no idea what that fixture needed to be until I found a video that's one of a series where this guy takes you through building an entire engine that Upshur published.  Late in the video, I got a good look at some prints he kept using, paused the video, screen captured the frame and improved its appearance. 


The fixture I'm making is at the upper right.  In the first picture, the 3/8" "peg" the designer calls out is lying on the top right edge of the print; the big 1" diameter cylinder that holds the peg is waiting to be drilled for it on the mill.  The peg is through-tapped, 8-32 instead of 6-32 because I prefer 8-32 screws.  Tomorrow, I should be able to complete the fixture and maybe make my first attempt at the cam.  A finished cam is in the middle of this screen capture, and it looks very much like the one I'm trying to make.  With this method, the cam is largely machined by hand; the fixture just makes it easier to hold the work for those odd cuts.

There's another method for cutting cams that has been shared by a home engine modeler named Chuck Fellows, and his video details how he got there.  It seems a bit fussier to set up than this, but probably gives a more controlled shape.  Fellow's method fixes the cam blank on a rotary table which then moves for all the cuts while Upshur's method uses a lot of hand work; tighten down the screw that holds the blank in place, make a cut, loosen the screw, change the blank's position, tighten the screw, make a cut, and repeat.  Over and over.  
 
The topic of making cams is of great importance for engine manufacturers, especially generating the curves mathematically.  I've read several things on this, including equations that can be plugged into an Excel-compatible spreadsheet.  Take this exercise:  the green circle is the starting blank; the big white circles cut the left and right flanks; the center points where the center of a boring head should sit while rotating to cut those big white circles are computed and displayed.  The boring head is cutting an inside diameter, not an outside diameter. 


This rabbit hole is as deep as you want to go and as techno-geeky as you want to get. 



Thursday, June 18, 2020

DARPA is Reviving NERVA - What?

It's a rule of writing for others to never use acronyms without explaining them.  Fully spelled out (so that it would be a two-line title) the Defense Advanced Research Projects Agency (DARPA) is opening bidding for contracts to revive the Nuclear Engines for Rocket Vehicle Applications (NERVA) program from the early days of NASA.

The basic problem is that moving things around in space is slow, ultimately because every molecule of fuel has to be lifted with you (for now) so using small amounts of fuel and taking a long time to get anywhere is a reasonable trade.  The idea of nuclear powered propulsion goes back to the earliest days of NASA.  Wernher von Braun, the German engineer who defected to the United States after World War II, started a program to develop systems before the moon landings.  That program, NERVA, eventually got closed down to help pay for the Shuttles.  See here for a NASA review of the program (pdf) and here for a video of a test firing
But now, the US Department of Defense is getting interested in space-based propulsion. Last month, through a presolicitation, the US Defense Advanced Research Projects Agency announced its intent to have a flyable nuclear thermal propulsion system ready for a demonstration in 2025.

Through this Demonstration Rocket for Agile Cislunar Operations, or DRACO program, the defense agency seeks technology that will allow for more responsive control of spacecraft in Earth orbit, lunar orbit, and everywhere in between, giving the military greater operational freedom in these domains.

"Activity in cislunar space is expected to increase considerably in the coming years," Maj Nathan Greiner, manager of the DRACO Program, told Ars. "An agile nuclear thermal propulsion vehicle enables the DOD to maintain Space Domain Awareness of the burgeoning activity within this vast volume."
There are a few ways to achieve nuclear propulsion; the most accessible (and probably the most politically acceptable) is nuclear thermal power in which a reactor super heats a fuel (probably hydrogen gas) and it expands through a nozzle.
In "Phase 1" of its solicitation, DARPA has asked industry for the designs of both a nuclear thermal reactor and an operational spacecraft upon which to demonstrate it. This initial phase of the program will last 18 months. Subsequent phases will lead to detailed design, fabrication, ground tests, and an in-space demonstration. No contracts have yet been awarded, and award values will be determined by industry submissions.

With the DRACO program, the US Defense Department could potentially move large satellites quickly around cislunar space. For example, moving a 4-ton satellite from point A to point B might take about six months with solar electric propulsion, whereas it could be done in a few hours with nuclear thermal propulsion.
It's arguable that this DARPA action is being brought along by other trends going on.  First is the creation of Space Force and the recognition of the value of the High Frontier.  Second, critical enabling technologies are maturing at the right times, such as better refractory materials (able to handle extreme temperatures); in a nuclear thermal engine, Hydrogen is stored at 19 Kelvin, while "the other end" of the reactor has hydrogen heated to 2500 Kelvin - or higher.  Third, NASA is working with BWX Technologies, the companywhich makes most of the nuclear reactors found on US Navy submarines and aircraft carriers, on the design of a reactor for Mars missions.


1960s artist's concept of a nuclear thermal rocket arriving at Mars.  The circular structure on the left is an aerobrake. 

DARPA has a reputation for producing some of the leading edge technologies in the world.  It seems they've decided the time is right to push this one along. 



Wednesday, June 17, 2020

Probably The Weirdest Story You Haven't Seen

In 2020, it's saying something to refer to a news story as the weirdest thing you've seen.  This story is definitely among the weirdest things I've run across this year; Wuhan flu and plagues of locusts have nothing on this.  I first saw this picked up at Ars Technica, but have since seen it elsewhere.

The US Department of Justice and US Attorney's Office in Massachusetts together announced that they had charged six former eBay employees with “leading a cyberstalking campaign" against a newsletter editor and publisher, which "included sending the couple anonymous, threatening messages, disturbing deliveries—including a box of live cockroaches, a funeral wreath, and a bloody pig mask—and conducting covert surveillance of the victims."
James Baugh, 45, is eBay's former senior director of safety and security, and David Harville, 48, is eBay's former director of global resiliency—both were arrested today and charged with conspiracy to commit cyberstalking and conspiracy to tamper with witnesses. Each charge "carr[ies] a sentence of up to five years in prison, three years of supervised release, a fine of up to $250,000 and restitution," the DOJ said.

The bloody pig mask was a Halloween mask and shipped via Amazon.com, a court document said. The mask arrived at the victims' home the same day one of the victims "received an email reporting that a 'Preserved Fetal Pig' had been ordered online to be sent to the Victims' house," the document said. A few days later, the victims "received a box of cockroaches" that was purchased from a roach breeder and seller.
The targets of the harassment were a couple from Natick, Massachusetts, who aren't named in the publicly released documents, but who run an online newsletter that covers e-commerce companies.  eBay managers felt the newsletter was unfair to the online auction giant.  One alleged victim is a reporter and editor for the newsletter, while her husband is the publisher.
"Members of the executive leadership team at eBay followed the newsletter's posts, often taking issue with its content and the anonymous comments underneath the editor's stories," the DOJ said.
You probably know the line from Shakespeare that goes, “Oh! What A Tangled Web We Weave When First We Practice To Deceive,” and this is quite a tangled web.  You should read the whole thing if you want the straight story.  Here's a snip. 
The alleged crimes took place in August and September 2019. Four other former eBay employees weren't arrested today but face the same charges. They are Stephanie Popp, 32, eBay's former senior manager of global intelligence; Stephanie Stockwell, 26, former manager of eBay's Global Intelligence Center (GIC); Veronica Zea, 26, a former eBay contractor who worked as an intelligence analyst in the GIC; and Brian Gilbert, 51, a former senior manager of special operations for eBay's Global Security Team. Harville is from New York City while the other five defendants are from California.

"It is alleged that in August 2019, after the newsletter published an article about litigation involving eBay, two members of eBay's executive leadership team sent or forwarded text messages suggesting that it was time to 'take down' the newsletter's editor," the DOJ announcement said. Another message from one unnamed eBay executive to another said "we are going to crush this lady," according to the charging document.

The "take down" message was followed by a three-part harassment campaign by the six defendants, the DOJ said. The first phase included anonymous deliveries such as "a bloody pig Halloween mask, a funeral wreath, a book on surviving the loss of a spouse, and pornography—the last of these addressed to the newsletter's publisher but sent to his neighbors' homes."


For their part, eBay said that as soon as they found out about this, everyone involved was fired.   Thatincluded the company's former Chief Communications Officer, fired last September.  It gets a little weirder: the CEO of eBay at the time of the incidents was Devin Wenig.  He was also let go of in September of  '19.  Being a CEO, there was a more public announcement than for the others let go last September.  The announcement said something intended not to scare investors, that "both Devin and the Board believe that a new CEO is best for the company at this time."  Was the ex-CEO the guy who said it was time to take down the newsletter?  Was his departure linked to this mess? 



Tuesday, June 16, 2020

The More That Covid-19 Gets Studied, The More It Looks Like a Paper Tiger

That's the conclusion of NPR, of all places, quoted in the Foundation for Economic Education (FEE) news mailing.  The conclusion is surprising for them, but not how they start - which is to discredit the W administration and the '03 war in Iraq.
The Iraq War WMD debacle is arguably the greatest expert “fail” in generations. The holy triumvirate—lawmakers, bureaucrats, and media—all failed to sniff out the truth. If any of them had, a war that cost trillions of dollars and claimed the lives of 100,000-200,000 people likely could have been avoided.

It would be difficult to surpass the Iraq blunder, but emerging evidence on COVID-19 suggests the experts—again: lawmakers, bureaucrats, and media—may have subjected us to a blunder of equally disastrous proportions.
They go on to say that mounting evidence says that the coronavirus is more common and less deadly than it first appeared.  Originally, the claims for the numbers who would die were wildly terrifying, and you probably know the many times those estimates were revised downwards.  Neil Ferguson, professor of mathematical biology at Imperial College London, predicted millions would die in the “best-case scenario.”  As FEE points out, Neil Ferguson said in 2005 that up to 200 million might die from bird flu worldwide.  About 100 did. Not 100 Million; 100.A bit too much reliance on models that aren't too accurate.

Similarly, Infection Fatality Rates were pegged in the 3 to even 5% rate.  In reality, no study I see says it's over 1%.
"The current best estimates for the infection fatality risk are between 0.5% and 1%," says Caitlin Rivers, an epidemiologist at the Johns Hopkins Center for Health Security.
With all due respect to Dr. Rivers, Dr. John P. Ioannidis published work last week reporting:
Infection fatality rates ranged from 0.02% to 0.86% (median 0.26%) and corrected values ranged from 0.02% to 0.78% (median 0.25%). Among people under 70 years old, infection fatality rates ranged from 0.00% to 0.26% with median of 0.05% (corrected, 0.00-0.23% with median of 0.04%).
Among people under age 70, a median Infection Fatality Rate of 0.04%  The horrific death rates from New York Generalissimo Cuomo shoving patients with Covid-19 infections into nursing homes can really skew those numbers.

The main thrust of Dr. Ioannidis' paper is that the lockdowns were - at best - unnecessary, and could have done more harm than good.   This is a theme coming out of research all around the world and that I reported on a month ago (almost to the day).  Marko Kolanovic, a physicist and strategist for JP Morgan, pointed out that a majority of nations saw declines in infection rates after the lockdowns were lifted.


As I said in that post a month ago, early on when people first started talking about this virus, before the lockdowns, before much information was out, I pretty quickly concluded that eventually everyone other than the very few people living hundreds of miles from human contact will get the virus and develop antibodies to it.  Some people, obviously, will die and every death is a tragedy.  Thankfully, it looks like well over 99% will recover from it just fine.
Early on in the spread of the disease, it was pretty easy to come to the conclusion that eventually everyone on earth will be exposed to this.  It's a new virus, and new viruses jump from animals to humans pretty regularly; it's simply how the world works.  I don't have strong numbers to base this on, but I believe the nationwide downward trend in new infections will continue downward, this numbers guy says the worst of the epidemic is over, but the virus will be back next fall.  It's my understanding that coronaviruses, as a group, are hard to create vaccines for.  The common cold is one of many such viruses that we're always exposed to, for example, and there's no good vaccine for the common cold, right?
EDIT: 6/17/20 7:38 AM - I left out a link to my old post, which has a very worthwhile graphic as well as background info.



Monday, June 15, 2020

SpaceX Changes Direction and Pops a New Tank

It seems like long ago - 17 whole days ago! - when we talked about SpaceX's SN4 "RUD" (Rapid Unscheduled Disassembly).  At the time I said SN5 was built and I had said, "There will be a few days work and SN5, which has been ready for weeks, will be transported to the test area."

It didn't turn out that way.  First, there was a lot of demolition and then expansion of the area where testing is done.  A new test stand was designed and built.  Concrete was poured for a new Vertical Assembly Building at the Boca Chica facility.  There were road closures and the implication SN5 or 6 would be taken to the test stand last week.  Around the first of the month, though someone had spotted an unaccounted-for tank dome outside the existing High Bay buildings.  Then the dome was identified as being made of a new alloy steel being considered for the fuel and oxidizer tanks on Starship.


The mystery dome.  Photo @bocachicagal for NasaSpaceflight

Then the mystery dome was assembled into a new test tank called SN7.  Eric Ralph, SpaceX correspondent at Teslarati, wrote today,
Just like its three predecessors, the newest test tank’s purpose is relatively simple: demonstrate – at full scale – the efficacy of SpaceX’s current manufacturing processes. Back when SpaceX built and tested the first two tank prototypes in January 2020, the company was in the midst of making big changes throughout its coastal Boca Chica, Texas Starship factory – a major leap forward compared to the methods used to build Starship Mk1. While the first tank made it to 7.1 bar (~103 psi) before failing, a second tank survived all the way up to 8.5 bar (~125 psi), as did a third separate test tank built about a month later. According to CEO Elon Musk, 8.5 bar is more than satisfactory for Starship pressure vessels to safely launch humans into orbit, offering a safety margin of more than 40%.
This weekend the tank was taken to the test stand.  It was talked about that this was a major revision to the tank, being built of a different steel grade than before, because it's considered better for cryogenic temperatures than the grade stainless steel they had been using.
The most obvious reason to build a new test tank after the success of full-scale Starship prototype SN4 is a substantial change in the steel alloy SpaceX is building rockets out of in South Texas. CEO Elon Musk has teased such a shift for almost a full year and it appears to have happened right on time – if not ahead of schedule. SpaceX currently uses 301 stainless steel for Starship production, while the new material – discussed earlier by Musk and confirmed by inscriptions on the exterior of what would later become the fourth test tank – is a slightly different 304 steel “with higher ductility” (malleability). 
I recall seeing the mystery dome marked 304L (I've just spent 20 minutes looking for the picture), and I looked it up on the Materials Web: 304L gets that improved ductility by using a lower percentage of carbon in the steel.

Today the tank was tested.  The comments are saying it was intended to be a test to failure and they succeeded at failing.



A commenter on YouTube quotes Elon Musk.  I'll have to go with his report since there's nothing on any of the spaceflight news sites I comb saying one way or another.
From Elon's twitter:"Tank didn’t burst, but leaked at 7.6 bar. This is a good result & supports idea of 304L stainless being better than 301. We’re developing our own alloy to take this even further. Leak before burst is highly desirable."
Note: the action starts about 30 seconds in to this 2:15 video.  Before that you'll see a set of straps over the tank, apparently to hold it to the stand and keep it from flying away in pieces should it fail like some previous tanks have failed. 



Saturday, June 13, 2020

We Were Treated to a Spectacular Launch This Morning

This morning at 5:21 AM EDT, the 8th bundle of SpaceX Starlink satellites launched into the night sky and we went out to watch from the side yard as usual.  The launch was the most visually spectacular launch either one of us could recall, and as Teslrati author Eric Ralph suggested, probably led to reports of UFOs and strange lights in the sky all along the east coast.  
Through a confluence of orbital dynamics and luck, SpaceX’s seventh Starlink launch of 2020 may have created one of the most spectacular light shows visible across the US East Coast in recent memory.

Likely to incur a massive wave of ‘UFO spottings’ across the Eastern seaboard, Falcon 9 lifted off from a Cape Canaveral, Florida launch pad at 5:21 am EDT (09:21 UTC), a bit less than a half an hour before dawn. Heading east (and up), the 70m (230 ft) tall SpaceX rocket took just three minutes to escape Earth’s shadow and meet the rising sun a bit ahead of the East Coast’s schedule – the light from which instantly backlit the plume created by Falcon 9’s second (upper) stage. Effectively replicating – in reverse – a similar phenomenon often seen after SpaceX West Coast launches shortly after sunset, this is the first time in quite awhile that the stars have (somewhat literally) aligned for a similar light show in Florida.
Mrs. Graybeard and I have lived near the Cape Canaveral/Kennedy Space Center complex since 1982.  Years ago, we concluded the prettiest launches are when it's dark on the ground and the rocket goes into sunlight as it climbs. 

Local sunrise is 6:26, and we're in the week of the earliest sunrise of the year.  The rocket appeared to go northeast, but stayed visible through the end of the second stage burn making it into orbit.  During daytime launches that's never visible.  Visually, when it got to first stage cutoff and dropping the booster, it was still a bright spot in the dark.  Moments after the staging occurred, the second stage moved into sunlight and the exhaust plume started to light up.  For the next several minutes, we watched this glowing, bluish circle enlarge around the bright rocket, and we could see the first stage brightly illuminated by the sun basically tracking along the same path but below it, clearly dropping away from the second stage and payload.  At this point in the flight, the rocket is traveling on a gentle slope into orbit, moving mostly straight away from us, so it's approaching the horizon and getting lower in the sky as we watch. The peak height in the sky from our vantage point is probably around where the first stage cuts off and gets dropped. The glowing bluish exhaust cloud eventually got to around 30 degrees diameter when the second stage cutoff. 

Teslarati published a long exposure of the launch, but because it collects several minutes worth of light, it doesn't really capture what it looked like.


After the second stage cutoff (SECO), we came back into the house, went to SpaceX on YouTube  and replayed the launch through first stage recovery on their drone ship, then stayed with it through the satellite deployments.   

It's worth noting that this launch was different than other Starlink Launches.  SpaceX has started a Ride-Sharing service for small satellites, sending three ~110 kg (242 lb) Planet SkySat imaging satellites on the way to their final orbits, “for a price so low that the company initially didn’t believe it could be real.”  The cost to SpaceX was to reduce their usual load of 60 satellites down to 58.  

Next launch of a Starlink mission is currently No Earlier Than the 22nd, a week from Monday.  That's a late afternoon mission, 6:20 PM, so no chance of a repeat of the light show. 



Friday, June 12, 2020

A Ham Radio Series 4 - Antennas, Tuners, and Analyzers

The whole field of antennas and how to get them to do what you want comes up regularly.  There's dozens of books on the topic and an article or two isn't going to get you expertise.  Things that I think might be important may not be relevant to how you want to operate.  I've written lots on this from a more or less "how do they work" perspective.
Lately, I've been playing with something like The Three Laws of Antennas, patterned after Asimov's Three Laws of Robotics.
First Law: anything you can put up works better than nothing at something.
Second Law: nothing is best at everything.
Third Law: whatever you can put up won't be as good as you'd like.  Unless you have a Jeff Bezos-level budget including the property to match. 
A friend once told me that “Engineering is the art of compromise” and antennas are a perfect example.  The three laws emphasize that, each in their own way. 

It's my experience that most hams don't go out and put up some sort of megabucks antenna installation as they're starting out, going instead for something that's a bit more of a compromise, so let's consider a compromise antenna.  This is a length of wire that can only be resonant at one frequency and unless that frequency happens to be in a ham band, you won't be able to use it.   It doesn't matter what antenna you pick in terms of this discussion: a G5RV multiband antenna; an Off Center Fed Dipole (OCFD) or just a random length of wire, end fed. 

As a general rule, transmitters are fussier about the exact impedance of the antenna than receivers are and you'll find that your transmitter might not put out power at all - especially if it's a solid state (transistor of some kind) final.  What you need here is an antenna tuner.  I prefer automatic tuners (autotuners) because I like pushing a button and letting it do the work.  There are many on the market; the first I owned was by LDG and I still have a couple of them. 

What's inside an antenna tuner?  An impedance matching network called an L network.  It's simply two parts in a configuration that looks like the letter L, if you lie on your side.   The two components can be a series L/shunt C, a series C/shunt L, both can be inductors or both can be capacitors.  There are eight possible configurations; four to match to higher impedance, four to match to lower.   It helps to visualize the direction of impedance change, to higher or lower impedance, if you draw it almost like a little ladder.  The shunt component is on the higher impedance side.  In this example, we're climbing up to a higher impedance load.  If the load was lower impedance, the shunt component would on the source side - still the higher impedance side.  Another thing I like about an autotuner is that I don't have to think about this.  I push a button and it finds a good solution. 



The autotuner is an L-network with a bunch of coils and capacitors with relays to switch the series and shunt components of the L-network end to end and change their values rapidly; series adding inductors or parallel adding capacitors.  The tuner tries a combination, measures VSWR, compares it to the starting value and goes through an optimization process to find the lowest VSWR it can get.  In the end though, it’s electrically two components.

If you shop for radios, you'll find that a number of models feature an internal autotuner; everyone I've seen is limited in the range it can tune to 3:1 VSWR or less.  By comparison, the external autotuners tune a much wider range of impedance, 10:1 or more.  There are also external tuners that are more than just a two component L network; they can tune even wider ranges.  I've had older model radios that tuned well beyond the 3:1 range, which is a fairly minor adjustment.  Newer radios have software that does that first measurement, sees that it's starting above the limit, and won't try to tune at all. 

Do you need an antenna analyzer?  What is an antenna analyzer, anyway?  An antenna analyzer measures the impedance of the antenna.  Some are manual, like the popular MFJ-259D, you set them on frequency and read off the Resistance and Reactance.  You need to tune the frequency and see how the reactance (X) varies to see if it's inductive or capacitive - if the reactance goes up with frequency, it's inductive and if reactance goes down, it's capacitive. 

The manually tuned analyzers like the MFJ are lacking in a lot of features, but you can trim an antenna for lowest VSWR with one.  There are many antenna analyzers that do a frequency sweep for you and save the impedance values, both resistance and reactance with sign, save plots, or even export files of your antenna data for use in antenna design (or redesign for new purposes). 



“In the old days,” we used to tune an antenna to resonance by turning down the transmitter power, keying it up, measuring SWR with an SWR meter, and keeping track of how it changes.  If you're putting together a station, you should consider an external autotuner if you have a radio that limits tuning to 3:1, and especially if your radio doesn't have a built in tuner.  An analyzer is a purchase that makes most sense if you plan to experiment with antennas or want to build more.  They make keeping track of changes in your antennas easier, too.  I have an analyzer (not made anymore or I'd show you a picture) and since I make little odds and ends around the shack, I use it to measure components as well as measuring antennas.  They're useful tools.



Wednesday, June 10, 2020

Tales From the Seattle Communist Enclave

Or You Just Can't Make This Shit Up.

According to PJ media, Seattle's breakaway communist enclave called CHAZ (Capital Hill Autonomous Zone) has encountered troubles with their independence.  The only assets they have are stolen, and people who steal other people's assets (that is, the people of CHAZ) will steal anything that isn't permanently attached.


As Divemedic pointed out on Confessions of a Street Pharmacist, the communists behind CHAZ are incredible hypocrites.  One of the first things they did was build a border wall.  I assume it was with stolen materials, like the road barricades they stole from America when they formed their little empire.  And then their border wall was stolen right back.  


Bryan Preston, writing over at PJ Media puts the thoughts together like this:
The CHAZ collective thanked the mayor for her gift of a six-block area of America the mayor does not personally own (and which includes about 500 homes of actual Americans) by storming city hall and demanding that she resign unless she disbands the police.
...
Call the police!

Right — CHAZ wants to disband the police. The police are over in America anyway, and American police have no obligation to help secessionist CHAZ.

CHAZ has no farms or orchards. CHAZ is paved over with streets and buildings. CHAZ cannot feed itself.
...
It’s a pity CHAZ has no indigenous lumber supply.

Or electricity. Or water supply.
There has been talk about putting an embargo around the CHAZ and starving them out.  Note that they report there are 500 homes in the area they've taken over.  That's got to be somewhere between 700  and a thousand innocent people that are hostages in the CHAZ.  Since that's Antifa, and they're a designated terrorist organization I believe there are protocols for situations in which terrorists hold hostages.  We assume the citizens are opposed to losing their property to Antifa, so free the hostages and if all the Antifa loons happen to not survive, those are the breaks.   


 

Tuesday, June 9, 2020

A Lot of Sanity in 15 Minutes

I'm a long time subscriber to Glenn Beck's internet streams, first signing up right around the time of the legendary “wardrobe malfunction” Super Bowl half time show.  Beck's right hand man for the life of the program has been Stu Burguiere and they talk about having worked together since the first days of the show in Tampa, Florida.  In my early days listening to them on the radio at work, I thought Stu was really the brains of the outfit and Glenn, who described himself as a rodeo clown, was essentially just that.  In the years since, I've come to regard them as a really good team that comes at problems from some very different directions.  Glenn is driven by his emotions while Stu is a much more logical thinker.  On his own shows and on the Blaze TV network he has done a segment called Stu-tistics, in which he takes a decidedly analytical approach to things.  The Glenn Beck show is another example of a situation where the sum is greater than the parts.

We've all seen some of the statistics thrown around about the riots and urban unrest going on.  We've seen Instagram remove the 2013 FBI crime stats because it violates their narrative standards.


Larger version at the above link (90 Miles From Tyranny).

Stu takes a look at some of these stats with a different take than I've heard anywhere else.  I thought the fact of the day Stu quotes is that 144 people a year die from constipation.  If the number we've seen elsewhere is correct that 10 black men were killed by the police last year, then they're over 14 times more likely to die of constipation than from being killed by a cop.  I've heard a lot of demands, but none for free Ex Lax. 


Over 60 people died from an unfortunate lawnmower incident but almost 700 people a year die falling out of bed.

Stu's point, and it's a good one, is that in a population of over 300 Million, something that affects 10 or 20 people is awfully hard do anything about.  All the data we can find that's from real academics and not race hustlers says the rate of these police killings has been declining for years.  If next year's statistics said it was 12 instead of 10, was that a horrible relapse or random variation?  What are the error bands? 

So the cities are going to de-fund police because some radical activists say so? 
  



Monday, June 8, 2020

As The Crew Dragon Test Flight and Work on Starship Continue

As the Bob & Doug Show continues, more formally the Demo 2 Test Flight of the Crew Dragon spacecraft, an interesting little modification to the existing NASA contract has gone through and is pointed out by a comment on the Teslarati news site.  You might have heard that NASA only wanted brand new Falcon 9 boosters for manned flights.  This contract modification, on the Federal Government's SAM.gov beta website says that they will allow reused Falcon 9s. 
THE PURPOSE OF THIS BILATERAL MODIFICATION IS TO EXTEND THE DEMO-2 FLIGHT TEST FROM TWO WEEKS TO UP TO 119 DAYS AND ADD THE REQUIREMENT FOR 45TH OPERATIONS GROUP DETACHMENT 3 (DET-3) JOINT TEST TRAINING FOR PCM-1 THROUGH PCM-6 IN EXCHANGE FOR ALLOWING REUSE OF THE FALCON 9 LAUNCH VEHICLE AND CREW DRAGON SPACECRAFT BEGINNING WITH PCM-2. [BOLD added - SiG]
My own view, worth nothing, is that a once-flown booster is probably the peak of reliability; everything has been thoroughly tested, then thoroughly reinspected afterward.  Obviously, the Demo 2 test mission isn't over until the capsule reenters the atmosphere, splashes down in the Atlantic, and the crew is safe and sound on board the recovery ship.  That should be the weekend of September 26th, if the Days From Date Calculator isn't mistaken.  The crew for the next Crew Dragon mission is already in training and undoubtedly has been in training for quite a while; Doug Hurley and Bob Behnken were assigned to this mission and worked with SpaceX for five years before this flight. 
Jim Bridenstine, explained during a pre-launch briefing that the next flight of the Crew Dragon could fly as soon as August 30. That flight, called Crew-1, would see the Dragon carry four astronauts to the space station for a six-month stay. On board will be three NASA astronauts Mike Hopkins, Victor Glover, and Shannon Walker — who will be joined by Japanese astronaut Soichi Noguchi. 
Meanwhile, work on preparing to resume testing the Starship prototypes continues.  The debris from SN4's RUD was largely cleared away the next day and the work of rebuilding all the damaged hardware has been underway.  The cause of the explosion was quickly isolated to Ground Support Equipment, a Quick Disconnect panel that's supposed to ease connecting and disconnecting fuel lines.  It's an assembly like this one, although this particular QD is on the Starhopper that flew last summer. 

Shortly after a post-launch briefing celebrating and discussing SpaceX’s inaugural astronaut launch on May 30th, Reuters reporter Joey Roulette was able to ask Musk about Starship SN4’s spectacular demise the day prior. The SpaceX CEO was quoted saying that “what we thought was going to be a minor test of a quick disconnect ended up being a big problem”, confirming suspicions based on careful analysis of public views of the explosion that it was caused by issues with Starship’s ground support equipment (GSE).
Reading the LabPadre video sidebar, it seems there was hope of moving SN5 to the test stand today but those plans were scuttled and the road closure postponed until Thursday, June 11, at 6AM to 2PM CDT.

Meanwhile, in addition to the Starship testing in Texas, SpaceX has their first four-launch month scheduled.  Four in a month isn't a huge improvement; their previous busiest was four launches in 32 days, but it's indicative of a continuing emphasis on getting better at what they do and improving their launch tempo.  Those are:
(the first launch was Wednesday night, June 3rd)
June 12 – 9th Starlink launch
June 24 – 10th Starlink launch
June 30 – GPS-III-SV03 launch 
With a June 30th launch - as usual, a “No Earlier Than” date - it doesn't take much of a delay to push that into July, but July 3rd is 30 days later, just not a calendar month.  It's interesting to watch, not so much for the milestone of four launches in a calendar month but seeing the cadence they're attempting to hold.  SpaceX has 14 commercial launches scheduled in the second half of 2020, while an additional 20-24 Starlink launches were talked about at the start of the year.  So far, they're off their stated goals, with it looking more likely they'll get 18 Starlink launches.  


SpaceX's Boca Chica, Texas, production and test facility.  From Elon Musk.  There's talk of building something the size of NASA's Vehicle Assembly Building to accommodate the Starship Heavy that is in development now.