First, it is a good day when I find a new Chappy Happy project on YouTube. Thank you Chappy Happy! You make us happy!
Second, even before I watched the full video, I could recognize the PAL VFO. This is an old CB device. You will find them at hamfests. I picked one up several years ago, knowing that I will someday use it as a VFO or for VFO parts. It is, after all, an LC VFO, and it is to be celebrated and used.
Chappy Happy turns his PAL VFO into a simple direct conversion receiver for the 25 meter SW broadcast band. He is on the west coast of North America and uses it to listen to Radio Japan. He uses a J310 RF amp and an NE602 Gilbert Cell mixer.
That is great, but there is a big problem in using a direct conversion receiver to inhale AM signals: Unless you can get the frequency AND the phase of the VFO to be exactly the same as the carrier, you will have distortion. You will not have this problem if the signal is SSB, but you will have it with AM or DSB.
I think I can hear the distortion on the Radio Japan signal. Can you hear the flutter? That is what happens with an AM signal being received on a DC receiver. This is why Doug DeMaw frequently warned that you could not listen to a DSB signal on a DC receiver without significant distortion.
What do you guys think? Can you hear the distortion? Should Chappy Happy turn this receiver into a simple superhet, perhaps something like the Q-31?
Here is a video of my Q-31 super het for the 31 meter SW band:
Again, thanks Chappy Happy! Please keep those projects coming!
The frequency 3885 kHz is inextricably tied to one of the most iconic military radios of World War II: the BC-611 Handie-Talkie (part of the SCR-536 radio set).
Manufactured by Galvin Manufacturing Corporation (which later became Motorola), the BC-611 was the world’s first ubiquitous handheld, two-way AM transceiver. It was the "walkie-talkie" you see clamped to the ears of infantrymen in every classic WWII movie.
The technical marriage between this specific radio and 3885 kHz came down to how the military deployed them and what happened immediately after the war:
1. The Channels Were Commandeered
The BC-611 could operate anywhere from 3.5 to 6.0 MHz by swapping out internal plug-in coils and quartz crystals. Because the U.S. government temporarily shut down all civilian amateur radio operations "for the duration" of WWII, the military freely assigned tactical frequencies right inside what used to be the ham bands.
For company and platoon-level communications, 3885 kHz became a standard assigned military channel.
2. The Great Surplus Avalanche
When WWII ended, the military had hundreds of thousands of BC-611 units, along with mountains of spare FT-243 crystal units, sitting in warehouses. The government liquidated them to the civilian market for pennies on the dollar.
Hams returning from the war snapped them up. Because these units were strictly crystal-controlled (you couldn't just spin a dial to change frequency), you were locked onto whatever crystal was inside. Since a massive portion of the surplus BC-611 inventory came pre-installed with the military's 3885 kHz crystal and tank coil, thousands of hams suddenly possessed portable AM rigs fixed precisely to that exact spot on the dial.
3. A Lasting Living Tradition
Even though a BC-611 only pushed out a fraction of a watt of AM power (using a tube filament battery and a 108-volt B+ battery), hams quickly realized that if they gathered on 3885 kHz, they could hear each other locally. Operators with larger, higher-powered home stations began parking on 3885 kHz as well, just to act as "big ears" to pick up the faint signals of the handheld walkie-talkies.
That specific frequency choice was entirely forged in the surplus markets of 1945 and 1946. Eighty years later, the tradition is so deeply ingrained that military radio collectors and vintage AM operators still hold a massive, synchronized check-in on 3885 kHz every year during the Dayton Hamvention weekend.
Jim was a prolific software developer for radio amateurs. He was the source of the Elsie program used by so many of us.
I had a very useful e-mail exchange with Jim in 2022 about envelope detectors. Much of the exchange was about a 2012 article that Jim wrote on this subject. I was looking for it just today. Unfortunately Jim's software business (and his websites) are all apparently tied up with the executor. I can't access them.
Does anyone out there have a downloaded copy of Jim's 2012 article on Envelope Demodulators that they could send to me?
It is a tribute to the contributions made by a radio amateur that even after his passing people are scrambling to find his articles and his software. Condolences to Jim's family.
Mike WU2D has an interesting series of videos on the simple detectors used in crystal radios. Mike's videos touch on a discussion that I had a few years ago with a member of the Vienna Wireless Association. I was describing how an envelope detector uses rectification to recover (demodulate) the audio from an AM signal. The club member dismissed this explanation and claimed that what really happens is that the diode simply mixes the carrier and the sidebands to produce audio. He claimed that the rectification "theory" was just a fable created to deal with people who really didn't know how mixers worked. See: https://soldersmoke.blogspot.com/2022/12/is-envelope-detection-fable-or-is-it.html
I was kind of disappointed by Mike's videos. He seemed to take an agonostic position on this issue. He framed it as "some people believe in the rectification explanation, and some people believe in the product detection explanation." As if both explanations are equally valid. They are not.
This morning, I asked AI about the two explanations. Here is what AI says:
Does a simple, single diode envelope detector function the same way as a product detector does?
AI Overview
No, a single diode envelope detector does not function the same way as a product detectorbecause the envelope detector is a non-linear circuit that recovers the audio from a full amplitude-modulated (AM) signal by following its envelope, while a product detector is a linear mixer that recovers the audio from various modulated signals (including DSB-SC and SSB) by multiplying the modulated signal with a local oscillator. Product detectors are more versatile and offer better signal quality than simple envelope detectors, which are limited to demodulating DSB-AM signals with a full carrier.
I know that AI sometimes gets it wrong, but I think that on this one, it has it right.
I don't think it is necessary to include discussion of modulation percentages nor diode biasing to clearly explain what is going on.
Even if you are using a very weak signal and are completely in the square law region of the characteristic curve, you are still essentially dealing with a form of rectification: portions of the signal on the positive side of the curve will experience less attenuation than signals on the negative portion of the input curve.
When we use a crystal receiver, we are relying on the rectification done by the diode -- even if the rectification happens in the square law region. After the crystal there is some low pass filtering. The envelope of the AM signal remains and this is the audio signal that we listen to. That is why we call it -- correctly -- an envelope detector. And as the AI says, an envelope detector funcions differently than a product detector.
This was a fairly typical session of the Old Military Radio Net. 3885 kHz AM 0500 local on Saturday mornings. (Distant listeners can tune in via WebSDR.) This clip shows W3EMD, N2CQR (me) and, N1SNG. Buzz W3EMD from the Hudson Valley of New York was on with his KWM-1. Normally he uses a BC-348 powered with a Dynamotor. Last week he told the group that someone had COMPLAINED about the noise that his mic was picking up from the Dynamotor. Geez! I told Buzz that we had been commiserating with him about this on the SolderSmoke podcast. Later in this morning's session I heard WU2D, WA1HLR, AJ1G, and others. I reported on an emergency De-Oxit spraying of my HQ-100's band switch, just minutes before net call up. I also noted that I had found a crystal for 3885 kHz; the radio gods have spoken (TRGHS).
I didn't realize that "tapesponding" had become so widespread. I know of two very prominent homebrewers (one now a Silent Key) who exchanged tapes. When I learned of this I asked if those tapes (which would have been a real treasure) were still around. Sadly, they had been destroyed, as, I suspect, were most of the tapes mentioned in this video.
I sometimes think that some of the on-the-air conversations about tech topics really should be saved for posterity (most conversations clearly should NOT be saved!). The internet provides a great forum for this kind of preservation. This happens, but only very sporadically and mostly in the AM world.
So there I was, early Saturday morning (earlier here -- we are one hour ahead of the East Coast) listening -- as I do -- to the Old Military Radio net. 3385 kHz AM. I use the K3FEF Web SDR in Pennsylvania. I heard a station that sounded familiar: Chris W4SVA. He said he was in the Shenandoah valley and was receiving on an R-390A and transmitting with a homebrew rig. I kind of remembered talking to a guy with a station like that. I searched through the SolderSmoke blog. No joy. Then I remembered it was probably a log entry. There he is, W4SVA. Here is his QRZ page: https://www.qrz.com/db/W4SVA I was almost certainly on the K2ZA DX-100.
Here's my log entry:
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12 August 2018
75AM W4SVA Chris in the Shenandoah, 15 miles south of Harrisonburg. Very FB. AM guy. Building rack-mount rig. Lots of HB stuff. Sent him the Shenandoah rocket pictures.
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I also heard Buzz W3EMD from the Hudson Valley -- the dynamotor was clearly audible. FB Buzz.
Thanks Chris. And thanks again to John Zaruba for the DX-100.
Mr. Carlson mentions that he is a ham radio AMer. He is also on SSB, but AM is, he says, his preferred mode. FB.
I got a real chuckle about the MVC switch position on the front panel. "Manual Volume Control" like "Manual Gain Control." I thought I had invented this term. You know, "real hams control their gain manually." This is why Farhan never put AGC in the BITX20. But it seems the Army Air Corps was way ahead of me with the BC-348.
Mr. Carlson makes it sound (!) like the Dynamotors are a thing of the past. Not true. Every Saturday morning I listen to the Old Miltary Radio Net and hear a number of Dynamoters spinning in the background. One belongs to Buzz W3EMB who uses a BC-348. Buzz has an SDR attached to the IF of his BC-348, which I think is an admirable mix of the old and the new. Those BC-348s are, after all, quite old. WWII old -- like 85 years old. And still working.
Paul has a good discussion of the importance of short lead length, and of mounting shielded capacitors properly, and of the usefullness of a good groundplane under the capacitor. Go Manhattan boards! Paul's presentation on how to identify the outside foil of a capacitor was very good, but I was wondering if you could also find out by using a file to remove some of the yellow insulation, then test with a DMM to see which terminal is connected to the foil.
"Lots of times you have to add solder to remove solder." Indeed.
The importance of testing for BOTH capacitance and leakage. Yes.
But why bother with "period correct" internal wiring harnesses, when you have already put a bunch of modern caps in there? I mean, I'm in favor of the re-capping, but this seems inconsistent with the need for "period correct" internal wiring harnesses.
When Paul first fired up the receiver, I was hoping he would disconnect the antenna to see how much band noise was getting through.
When Paul got to the IF alignment, he spoke of the dangers of working on energized high-voltage gear. I had been thinking about getting a BC-348 myelf, but Paul's comments reminded me of why this is probably not a good idea for me. Paul's comments about "knowing where your hands are" is on target. "One hand behind the back, " is a good rule for this kind of energized testing -- this will help prevent current from a mishap from flowing through your chest.
I may have more comments later. Off to the beach now.
Back from the beach:
"Contrary to popular belief, the simpler the receiver, the better they hear." Amen Mr. C.
Paul's heroic cleaning of the 915 kc crystal made me feel like a wimp for not having tried to do this with some "bad" 455 kc rocks I was given while trying to build the Mate for the Mighty Midget receiver. I may go back to those crystals and try to clean them as Mr. C did.
The grand finale of this 2.5 hour video was, as expected, a demonstration of how good it sounds. But unfortunately it did not sound good. Paul tuned through the 40 meter band and I heard NO CW signals. I didn't even hear FT8. There were a few anemic SSB signals and, as he reached the upper portion of the band some very weak AM broadcast signals. I didn't even hear CHU Canada's time signal. Huh? Why? Our very simple homebrew Direct Conversion receiver sounds a LOT better than that. I mean look at the sweep of 40 meters that I did using only a simple dipole: https://soldersmoke.blogspot.com/2024/12/an-evening-bandscan-on-40-meters-using.html Why is there such a big difference in performance?
Could it be the antenna that Paul was using? He was on what he calls the 369 antenna. Could there be a problem in the receiver? Could it be band conditions?
OK, the title of this blog post has an element of click bait in it. Just this morning I was listening to the Old Military Radio Net on 3885 AM. I'm sure some of those guys would disagree with the assertion that SSB is better than AM. But I think this old Air Traffic Command video lays it out very well.
I kind wish they had dicussed Double Sideband, Suppressed Carrier transmission.
I wonder want the year of production of this video was. Does anybody know?
For the record: I am the owner of a DX-40, a DX-60, and a DX-100. I also am on 10 meter AM with a converted CB rig. So I have transmitted both sidebands, and the carrier.
I threw this in the bag on the way to the DR, almost as an afterthought. But I am glad I did. Today, watching reports on my 10 meter CW beacon (Mike WN2A provided the keyer), I noticed that my signal was unusually strong. At W3POA I was 7 db above the noise. At DF2CK I was 4 db above the noise. So I switched to the 10 meter AM rig (which is a converted GE brand CB rig) and worked John G3YPZ (see video above). I was running about 5 watts to a quarter wave vertical. But the signal reached the UK.
I was listening to the Old Military Radio Net this morning and I heard Tim WA1HLR talking about some contacts that he had made on 10 meters, near 29 MHz. So I pulled my modified CB rig off the shelf, connected a power supply and my 10 meter vertical, and began to listen. Soon I heard CQs! One from G4ITR and then one from G4VZR. I now have high hopes for at least one QSO. So please, point those ten meter beams at the Dominican Republic and give me a call. I am on 29.005 Mhz.
This is probably Jean Shepherd's best program about homebrew ham radio. It is about how we can become obsessed with the problems that arise with equipment that we have built ourselves, and how normal people cannot understand our obsessions.
I posted about this back in 2008, but I was listening to it again today, and quickly realized that it is worth re-posting. Realize that Shepherd's Heising modulation problems happened almost 90 years ago. But the same kind of obsession affect the homebrewers of today.
Note too how Shepherd talks about "Heising" in Heising modulation. Heising has an entire circuit named for him, just like Hartley, Colpitts, and Pierce of oscillator fame. Sometimes, when I tell another ham that my rig is homebrew, I get a kind of snide, snarky, loaded question: "Well, did you DESIGN it yourself?" This seems to be a way for appliance operators to deal with the fact that while they never build anything, someone else out there does melt solder. They seem to think that the fact that you did not design the rig yourself makes your accomplishment less impressive, less threatening. This week I responded to this question with Shepherd's observation -- I told the enquiring ham that my rig is in fact homebrewed, but that I had not invented the Colpitts oscillator, nor the common emitter amplifier, not the diode ring mixer, nor the low-pass filter. But yes, the rig is homebrew, as was Shepherd's Heising modulator.
Guys, stop what you are doing. Put down that soldering iron, or that cold Miller High Life ("the champagne of bottled beer") and click on the link below. You will be transported back to 1965 (and 1934!), and will hear master story-teller Jean Shepherd (K2ORS) describing his teenage case of The Knack. He discusses his efforts to build a Heising modulated transmitter for 160 meters. He had trouble getting it working, and became obsessed with the problem, obsessed to the point that a girl he was dating concluded that there was "something wrong with him" and that his mother "should take him to a doctor."
This one is REALLY good. It takes him a few minutes to get to the radio stuff, but it is worth the wait. More to follow. EXCELSIOR! FLICK LIVES!
Joe KA1BWO is a well-known AM operator who moved West to Idaho several years ago. We had a very nice contact on 10 meter AM on January 14, 2024. See the video above.
I was using an old CB rig that I had converted to legitimacy on 10 meters using the mod developed by Jerry K5JC:
Eldon did the mod and we have been trying to make contact. We did so today. It was very cool. I was on my GE rig; Eldon was running a JC Penny! (See video above.) 1054 miles. Thanks Eldon. And thanks Jerry!
See video above. This happened on my second day on 10 meter AM. I was using the little GE CB radio that I had modified for 10 meters. I had lucked out. First bit of luck: the CB that I bought (for parts!) at a hamfest turned out to be just the thing I needed for a quick and easy mod. The GE box had what is called a Hygain board and -- most important -- a PLL02 chip. Second bit of luck: I stumbled across an article by Jerry K5JC on how to put this particular kind of device onto 10 meter AM. Boom, Bob was my uncle, and I got on 10. Then, today, the miracle happened. I heard Benny K5KV and I gave him a call. He asked about my rig. I described the mod to the GE CB. Benny seemed kind of surprised, and for good reason. You see, Jerry K5JC (the guy who created the mod that I was using) had just broken squelch on Benny's rig! Benny told him to get on 10 and soon I as in contact with the guy who had created the mod that I was using. The Radio Gods Have Spoken. Thanks Benny and thanks a Jerry. This was all really cool.
Think of odds of this happening: On my second day on 10 AM, running just 4 watts, I just happened to contact Benny K5KV in Texas who just happened to be in 2 meter range of Jerry K5JC, who just happened at that moment to be breaking squelch on Benny's 2 meter rig. TRGHS.
Here we have a Michigan Mighty Mite being modified for AM in Romania, with input from Hungary, and inspiration from Melbourne, Australia (Peter Parker VK3YE). With a very nice shout-out to SolderSmoke.
I really like Ciprian's emphasis on having fun with the electronics.
Helge is an amazing homebrewer. Check out the shack. Note the R-390 and the Tek 'scope. Watch how Helge designs his rig. Watch him check the 3-D printed coil and the variable caps for resonance. Most of all, watch his happiness when the new transmitter works. I just wish he would have showed us some OM complaining that he was on the "wrong" sideband. FB Helge! Thanks.
Jose CO6EC sent us more information about homebrew rigs built in Cuba. The transmitter above is a thing of beauty. I am really glad that Jose has held on to it. Thanks Jose!
Jose CO6EC today
Jose CO6EC writes:
This is another work from that time: an AM and CW transmitter of about 100W of power, with an on-board modulator. It was taken with some modifications from a Handbook from the 50s. Here goes: it was built with what we had on hand at that time, it still exists, I keep it as a relic of those years.
It used combined Soviet and American tubes in the RF sections: Soviet 6P9 and (2) 6146. The modulator used Soviet 12AX7, 12AUT and (2) 6P7. The 6P9 works as a crystal oscillator, and in case of using an external VFO it works as an amplifier and doubler or tripler to obtain outputs in the 160,80,40,20,15 and 10 Meter bands.
The VFO was also taken from a 1949 Handbook if I remember correctly, but I don't have any literature on that, as you can see in the photo it has 5 5u4c rectifier valves, VR150 voltage stabilizer, 6v6 output, another 6v6 as a separator and a 6 )I(4 (60I94?) Soviet, in the oscillator. The stability they achieved in those years is incredible, I could communicate with stations that were on LSB and if I didn't tell them that I was on AM they didn't notice.
As a receiver I used an old Soviet AM and CW receiver, used by the Aviation HF stations of the 40s, which no longer exists hihihihihi
I'll tell you how I tuned all that good ftuff: First I put the receiver in CW to beat the signal of the stations in SSB. After hearing them clearly, I removed the oscillator of the receiver and connected only the VFO of the Transmitter, and beat the signal with that of the receiver until I heard the other station clearly, then I put the transmitter to work and was ready to communicate.
There were many communications made with that station, even internationally on phone and CW.
Today everything is easier because with transceivers it is not necessary to go through all that work, but it is always good that those who did all this work know how radio was built and made.
73 Jose CO6EC
Obviously the transmitter
The two pictures above must be the VFO. It looks like the VFO in the 1947 ARRL Handbook.
I wonder what handbook this was? Spanish language.
I will be sending you some work of homebrew from the 80's and 90's when practically everything was manufactured by Cuban radio amateurs
The photos are of a Modulated Amplitude TX for the 160 Meter Band, about 25W of which several were made. The final tube was modulated in many cases by a 6DQ6, 2E26 or other similar ones that were very abundant at that time.
This one in particular ismade with valves6BH6 for the VFO, 6CL6 for the amplifier step and 6P23 Soviets in the final part, the modulator was made up of a 12Ax7 microphone preamplifier and a 6BM8 that came out through the cathode to the screen grid of the 6P23, in this way the carrier was controlled by modulation what we calledCarrier Controlas there was no voltage on the grid at the ends there was practically no carrierin the air which gave the impression of transmitting in SSB. hihihihihihi
For those who did not have a communications receiver, a conventional radio was adapted to receive that band, which in many cases was a VEF-206 of Soviet construction, to which an oscillator was adapted to beat the signal and get exactly on frequency. This was very popular here in the late 80's and early 90's.
Thanks Jose. We look forward to learning more about Cuban homebrew. The way in which radio amateurs got on the air with gear that they made themselves using the limited parts available to them is really interesting and admirable. 73 Bill
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