I first saw the link to Onno's site on Peter VK2TPM's blog. And at first I confused it with the site of another great homebrewer Miguel PY2OHH. This is all very IBEW: On the website of an Australian ham, I spot the web site of a Dutch ham living in Spain and briefly confuse him with a Brazilian homebrewer with a very similar callsign. TRGHS.
Onno PA2OHH has an inspirational approach to the hobby that he presents in a really wonderful website. Here is his intro to Barefoot Radio:
Barefoot technology and Barefoot power!
Barefoot technology or simple, non-professional radio technology and real Barefoot power or harmless QRP power, that is what you will find here. There are some complex designs but many designs are simple radio amateur circuits. They will never be used professionally! These simple circuits and rigs can give you much fun: home brewing, portable activities during holidays, etc. Batteries and inverted V dipole antenna's with a fishing rod as the center support are all you need to make many QSO's.
Much fun! Barefoot technology and Barefoot power can give you much fun, but is not perfect... There are disadvantages like VXO control instead of a VFO, direct conversion receivers that receive both sidebands and simple frequency displays that are not so easy to read. But working with such simple equipment is often more exciting than working with a much better commercial transceiver. Perhaps that you cannot believe that you can make many QSO's with QRP power of only 1 watt. Indeed, some practice is needed in the beginning so do not give up too soon. Every boring standard QSO becomes an exciting experience with QRP power!
I spent most of January in the tropics, away from my workbench. This seems to have had a good effect on my 17 meter split TX/RX project. As I was leaving, heading south, I was thinking about several difficult options to deal with my spur problem (see previous blog posts). I thought about turning the transmitter into a transceiver by building a receiver board. I thought about putting San Jian frequency counters on both the transmitter and the receiver, then doing a visual numerical "netting" by just putting the two devices on the same frequency (I actually ordered 3 San Jian counters). The counter option was even more complicated than it at first seemed -- I would have to build a converter to shift the RX VFO frequency up. VK2EMU suggested a tube type "Magic Eye" (interesting idea, but also complicated). This was getting out of hand.
When I got back home, I took a new look at the problem. I decided to take one more shot at suppressing the 8th harmonic of the carrier oscillator. I had already built a new oscillator and buffer using the circuit from Farhan's BITX20. And I had put it in a metal box. Now I decided to do three things:
1) Tighten up the low pass filter at the output of the buffer by moving the cutoff frequency lower (to around 7 MHz) thereby getting a bit more suppression at 41 MHz
2) Try putting a series LC shunt circuit tuned to 41 MHz at the output of the carrier oscillator (between the oscillator and the buffer).
3) Reduce the voltage to the oscillator/buffer. I have this on a pot, so I can adjust it down to the point where the remnant of the harmonic is no longer audible, while keeping the main carrier osc signal sufficiently strong.
It seemed to work. I could now hear the desired frequency for spotting, without the confusing tone from the spur.
Why had I been able to do this back in 2002 in the Azores using a simple trimmer cap to ground? My guess is that I was using my Drake 2-B as the receiver. The trimmer cap to ground may have reduced harmonic output. And I was probably cranking back the RF gain on the 2-B to the point where I could hear the desired signal but not the remnants of the spur. I have no RF gain control on the Barebones Barbados receiver that I am using in this project.
So, what's the lesson from all this? Well, if you are faced with a serious technical problem, and you find yourself considering complicated and difficult solutions, go to the Dominican Republic for about a month (especially if it is January or February), and then take another look at the problem when you return. If you are unable to travel this far or for this long, taking a walk or taking a weekend break from a troublesome problem will likely have a similar mind-clearing effect.
The video above shows part of a February 1, 2022 QSO with Gar WA5FWC using the split TX/RX 17 meter rig. Gar is an amazing long-time SSB homebrewer who got his start with phasing rigs back in the day.
So there I was, innocently checking the lower end of the tuning range on my now 17 meter SSB Barebones Barbados W4OP receiver. I had it tuned to the bottom of the 17 meter phone band. All of a sudden I hear YV5B in CW. It was obviously a beacon transmission.
I had forgotten about these beacons. Some quick Googling brought me to a very up-dated web site:
The site shows exactly which station is transmitting at any given moment. There is also a very handy map display giving beam headings and distance from your location.
So far, I'm only hearing YV5B and VE8AT. I hope to hear more once the Coronal Mass Ejection is behind us.
Check it out. Leave your receiver on 18.110 MHz. Let us know what you are hearing.
In several of the articles that I have seen about the homebrewing of VFOs the authors seem to throw up their hands when the subject of temperature compensation comes up. They seem to just say, "This is hard. Not for the faint of heart. Good luck with that!" But in this great video Mike WU2D shows us in very practical terms how to do temperature compensation of VFOs. This is really great news for those of us who prefer old style coils and caps to Si5351 chips. Thanks Mike!
I first came across the above picture of K0IYE's inspirational, completely homebrew station many years ago in the pages of "World Radio" magazine. I have already linked to Frank's book many times over the years, but it is so good that I regularly feel compelled to write about it again. Frank updates the book. Just check out the introduction to his website. Frank even has a Spanish language version of his book. All for free. Thank you Frank.
The introduction to Frank's web site:
Over the last century amateur radio has evolved into numerous different
hobbies. Some hams enjoy weekend contests in which they try to
contact as many stations as possible. Others talk to as many of the
world's 341 call areas as possible and collect QSL cards to prove it. Other
hams just like to ragchew with friends. Still others communicate over
long distances at UHF frequencies using satellites, meteorites, aurora and
other substitutes for a sunspot-charged ionosphere. Some hams provide
communications for their communities during emergencies.
Many of us have returned to the early days of radio by building our own
equipment from scratch. Most home builders start by building QRP (low
power) transmitters. If this doesn't satisfy your urge to build something,
you can move on to build the entire station. That is what this website is about.
Great stuff from Mike and from Frank Harris K0IYE. But when I put the VFO in a box, I usually try to put the frequency determining components (the coil and most of the caps) in the box, with the powered components (transistor, Zener, voltage dropping resistors) outside the box. If I put these powered components in the box, I find there is some drift as these components slowly heat up the interior of the box.
Dean KK4DAS and he VWS Builders have just stated building analog VFOs, so Mike's video is very timely for them.
I told Farhan that the world NEEDS a homebrew Raspberry Pi observatory at Lamakaan in Hyderabad. They are on it.
This looks very do-able. And fun. And UHF. And SDR. And Raspberry Pi.
I'd like to build one too. I was encouraged by the video demo -- it was done in Alexandria, Virginia, very close to where I live.
A while back I was lamenting to Dean that I reluctantly threw away a DISH or DIRECT TV satellite TV antenna. I worried that I had discarded something that would have been useful for radio astronomy. Turns out I didn't need it. This video and the associated .pdf shows how to look at the galaxy with a simple homebrew (Home Depot!) horn.
As often happens, I may have jumped the gun in declaring the exorcism of my 17 meter transmitter to be a success. As readers of this blog will recall, my problem was that when trying to "net" my separate 17 MHz receiver and transmitter, at around 18.116 MHz I could hear more than one tone as I tried to get to zero beat. The 8th harmonic of my 5.176 MHz carrier oscillator was mixing with the 23 MHz VXO signal and producing a spur. I could probably knock the level of this spur down below FCC limits, but -- and here is the problem -- I probably could never knock it down to the point that it would not be audible in the sensitive receiver that sits right next to the transmitter. So this is really a netting problem, not really a spur problem.
I don't want to try another filter frequency -- I have VXO crystals that really work only with a filter at 5.176 MHz.
So here is my current idea: Build a receiver board and turn this thing into a transceiver. Switch with relays the input and output of the 5.176 MHz filter, and use relays to switch to the receiver board the VXO and carrier oscillator signals.
Making this thing a transceiver would eliminate the need for netting. This should solve my problem.
First, thanks to all who sent in suggestions. They came in literally from around the world, and this is a demonstration of the IBEW in action. I used or at least tried all of them. They were all good ideas.
Following Vasily Ivananeko's pseudonymous suggestion I rebuilt the carrier oscillator (apologies to G3YCC). I used the carrier oscillator/buffer circuit from Farhan's BITX20.
Henk PA0EME said I should look at the signal level at the input ports of the NE602 mixer. Henk was right --- the VXO input was far too high. I lowered it, but the problem persisted.
At first, I thought that the spur in question was so small that it would not show up on the air. I could not see it in the TX output using my TinySA spectrum analyzer. That was good news and bad news: Good that it was not showing up on the air, bad that I could not see it in the TinySA and use that image in the exorcism.
At first I thought that the spur was being caused by the 10th harmonic of the carrier oscillator and the third harmonic of the VXO. This seemed to fit. So, following VK3YE's sage advice, I built a little 69 MHz series LC trap (using a coil sent by AA1TJ, on a board CNC'd by Pete N6QW). That trap succeeded spectacularly in crushing the 10 harmonic. Look at these before and after shots on the TinySA:
Before Trap
After Trap
Spectacular right? But guess what? The problem was still there.
I scrutinized the situation once more. I realized that the spur would be more visible if I put the TinySA on the input of the transmitter's PA (a JBOT amp designed by Farhan) as opposed to putting it on the output. Watching the spur and the needed signal move in the TinySA as I tuned the VXO, I realized that they were moving in opposite directions. This indicated that the spur was the result of a carrier oscillator harmonic MINUS a VXO-generated frequency (as the VXO frequency increased, the spur frequency decreased). Looking at my EXCEL spread sheet, I could see it: 8th harmonic of the carrier oscillator MINUS the main output of the VXO.
To confirm this, I plugged the values into W7ZOI's Spurtune program. Yes, the spur popped up and moved as predicted.
For further confirmation I shut down the carrier oscillator by pulling the crystal from the socket, and then just clipped in a 5.176 MHz signal from my HP-8640B signal generator (thanks KB3SII and W2DAB). Boom! On the TinySA, the spur disappeared. Now I at least knew what the problem was: a harmonic from the carrier oscillator.
Following good troubleshooting practice, I turned off the gear and went to bed. When I woke up, an idea came to me: Before launching into a lot of filtering and shielding, just try running the carrier oscillator at a lower voltage, seeing if doing so might reduce the harmonic output. I disconnected the carrier oscillator board from the main supply and clipped in a variable voltage bench supply. Watching the signal on my TinySA, I watched as the spur completely disappeared as I reduced the voltage from around 13V to 10V (see video above). The main signal frequency level did not change much. I tested this by listening for the hated extra tones. They were gone. Exorcised.
Key lessons:
-- Spur problems are difficult to troubleshoot. Armstrong's superhet architecture is, of course, great, but this is definitely one of the pitfalls. Single conversion makes life easier. IF selection is very important. Choose wisely!
-- When looking at the TinySA as you tune the rig, pay attention to which way the spur is moving. This provides an important clue regarding the combination of harmonic you are dealing with.
-- The TinySA is a very useful tool. It seems like it is easier to use than the NanoVNA (which is also a fantastic tool).
-- It can be fun and rewarding to re-visit old projects. In the years between original construction and the re-look, new test gear has become available, and the skill and experience of the builder has improved. So problems that once seemed insurmountable become fix-able.
-- Thinking through a problem and thinking about possible solutions is very important. It pays to step away from the bench to think and rest. Rome wasn't built in a day. Here's a rough block diagram that I drew up (noodled!) while trying to figure out this problem:
Thanks to the Antique Wireless Association for this really wonderful video, and for their involvement in the 100th anniversary event. Special thanks to Ed K2MP.
On December 11, 2021, the 1BCG team in Connecticut had some technical difficulties. As we all know, that is part of being a radio amateur. Details of the problems are presented here:
Good thing Paul Godley ran into Harold Beverage on the ship going over.
And imagine me complaining about having to step out into the carport to adjust my antenna -- Godley had to trek one mile THROUGH SEA-WEED to adjust his. Respect.
Farhan VU2ESE kindly invited us to talk to his Lamakaan Amateur Radio Club. They did a simulcast through the QO-100 Geostationary Satellite. This picture shows N2CQR being beamed into India from 22,500 miles. Note the ET-2 and the Mythbuster on the bench. This was a lot of fun. Thanks Farhan!
Here we see them struggling to find the proper frequency for one of the oscillators in a dual conversion UHF receiver from the Apollo program. For the VCO, they needed a crystal in the 23 MHz range. They faced the same questions we face: Series or parallel? Load capacitance? Fundamental or overtone?
It just so happens that at this moment I have on my bench the 17 meter SSB transmitter that I built some 20 years ago. And the VXO in it uses crystals in the 23 MHz range. TRGHS. (More on the spur problem with this rig soon. The solution does involve the 23 MHz VXO.)
Very cool that CuriousMarc found a manufacturer still willing to produce custom-made crystals. JAN flashbacks! LapTech Precision in Canada: https://www.laptech.com/index.php
The video above is Episode 8 in the Apollo Comms series. If you go back one episode, you can watch Marc and his assistant troubleshoot the NASA Apollo UHF receiver. They use very familiar troubleshooting techniques. This reminded me a lot of what we do with older, potentially modified gear. They were able to figure out what was wrong and how a mod had changed things. This set the stage for the crystal replacement selection we see in Episode 8. Here is Episode 7: https://www.youtube.com/watch?v=87qA41A_Ies
Note: The frequencies in this Apollo receiver were listed in Megacycles, not Mega Hertz.
Thanks to Bob Scott KD4EBM for alerting us to this.
Last month we were talking about this company. Someone thought it was run by Lew McCoy of ARRL Homebrew fame, but it now appears that our Lew McCoy was not involved in the company.
Note how they provide TWO carrier oscillator/BFO crystals for each 9 MHz filter, one for USB, the other for LSB.
They were pricey too: In 2021 dollars, that Golden Guardian would cost $390.
This is really beautiful. Radraksha Vegad (Pargrahi) from India built a discrete component version of the venerable 555 timer chip. He built it on wooden blocks. This leads to the kind of understanding that even Jean Shepherd would have admired. No longer is the 555 a little mysterious black box. No, Pargrahi shows us how it works.
I know we could do something similar with the NE602 or the LM386. But probably not with an Arduino microcontroller or an Si5351. And that says something about understanding and complexity.
I built the transmitter almost 20 years ago. It is in the larger box, which originally housed a Heathkit DX-40. There is a lot of soul in that old machine. Details on this construction project are here: https://soldersmoke.blogspot.com/2021/12/junk-box-sideband-from-azores-2004-qst.html(The smaller box is a Barebones Superhet receiver set up for 17 meters.)
In the 2004 QST article I discuss a problem I had with "spotting" or "netting." This is something of a lost art, something that you had to do back in the pre-transceiver days, when running a separate transmitter and receiver. This was how you got the transmitter on the receiver's frequency. Essentially you would turn on the carrier oscillator and the VFO and let a little signal get out, enough to allow you to tune the VFO until you heard zero beat on the receiver. My problem was that around one particular frequency, I would hear several zero-beats. This made netting the receiver and the transmitter hard to do.
Important note: This is really just a problem with the "netting" or "spotting" procedure -- the problematic spur does not show up in any significant way in the output of the transmitter. I can't see it on my TinySA. But it is strong enough to be heard in the unmuted receiver sitting right next to the transmitter. And that creates the netting problem.
In the QST article, I said that I noticed that the problem seemed to be centered around 18.116 MHz. As I approached this frequency, the tones -- desired and unwanted -- seemed to converge. That was an important clue. In the article I said I thought that I could eliminate the problem with just one trimmer cap to ground in the carrier oscillator, but looking back I don't think that this really fixed the problem.
I recently took a fresh look at it. Exactly which frequencies were causing the unwanted signals that appeared in my receiver?
I used an Excel Spread sheet to find the culprits.
The first column shows the carrier oscillator and its harmonics. The second column shows the VFO when tuned for a signal at 18.11668 MHz (23.2927-5.17602), along with its harmonics. Check out the 10th harmonic of the carrier oscillator and the third harmonic of the VFO: 69.8781-51.7602 = 18.1179. Those two harmonics would produce the problem I had been experiencing.
I turned to one of Wes Hayward's programs for confirmation. Spurtune08 came in the EMRFD software package. Here is what I saw when I plugged in the above frequencies:
You can see the little spur off to the left of the main signal. In the program, as I tune the 23 MHz VFO frequency, the spur moves closer to the main frequency as I approach 18.116 MHz, just as it does in the real rig. Note that I have only turned on the 10th harmonic of the carrier oscillator and the 3rd harmonic of the VFO. Spurtune08 is very useful. Thanks Wes!
So, what is to be done? For now, I am just restricting my operations on 17 meters to above 18.120 MHz. (I worked several DX stations with it on December 27.) But obviously I need to fix this. This rig needs an exorcism. I think I only need to get rid of one of the harmonics, and the 10th harmonic of the carrier oscillator seems easier to kill. I'm thinking of putting the carrier oscillator in an Altoids box, and then adding some filters to knock down the 10th harmonic.
Here is the G3YCC schematic that inspired this rig. I used G3YCC's carrier oscillator and balanced modulator circuits, just using a 5.176 MHz crystal and changing the tank circuit in the collector:
How would you folks knock down that 10th harmonic?
