"If it moves and its not supposed to, you use duct tape."
Monday, May 19, 2025
Sunday, May 18, 2025
Rick N3FJZ's Early Completion of the SolderSmoke Direct Conversion Receiver Challenge
It was a cold day in early February 2023. Rick N3FJZ had responded to an early version of the SolderSmoke Direct Conversion Challenge:
I wrote:
Rick N3FJZ has completed his the direct conversion receiver that we will soon be building with students at a local high school. See video above.
We are hoping that a number of people will build the receiver as we designed it. Some folks have sent us versions of the receiver that they have built, but these versions often include significant deviations from our design, rendering them less-than-useful in checking our work. Rick built it just as we prescribed. His build is very useful in confirming the validity of our design. So if you are working on one of these receivers, I would encourage you to -- for the moment -- dispense with innovations and build it the way Rick did: as per the design we have been using.
We know that our design is not perfect. But we have decided to stick with it because it is very simple and very easy to explain. Examples: We know there is an impedance mismatch between the mixer and the AF amp. But fixing this would introduce complexity that we want to avoid. And the receiver works fine with the imperfection. We know that a push-pull AF amp would probably work better than the one we have. But we do not want to have to explain push-pull amps, biasing schemes, and PNP transistors in this short introductory course. So we stuck with three common-emitter AF amp circuits and an 1K-8ohm transformer.
Rick did a really excellent job not only in building this receiver, but also in documenting it. His diagrams and drawings are really superb. We will probably use these in our presentations to the students:
We will keep all of you informed on the progress of this project. We will begin this week. But if you are still working on the receiver, please send us your work, even if it comes in after we begin the course.
Thanks Rick!
-------------------------------------
Thanks indeed Rick. Sorry it took so long to put you in the SolderSmoke Challenge Hall of Fame, but you are in now, and you definitely deserve it. Congratulations OM.
I especially like your finding the audio ourput transformer in an old transistor radio. Too often we see builders quit after discovering that Mouser or some other supplier no longer stocks the needed part. You show that homebrewers have other sources available, if they are willing to scrounge a bit. FB. I also liked the switch that helped compare the outputs of the two AF transformers. Very useful.
Thanks too for all the great videos and your really nice documentation -- we have used your work quite a lot.
73 and welcome to the Hall of Fame!
Rick N3FJZ
____________________________
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Saturday, May 17, 2025
Stephen VK2BLQ's Very FB EARLY build of the SolderSmoke Direct Conversion Receiver
This was back in the old days, long before we had Discord. It was early 2023, and we were getting ready to start the Direct Conversion receiver project at the local high school. I put out a version of the SolderSmoke Challenge: I asked people to build our receiver and let us know if it worked for them. Stephen VK2BLQ took us up on this and built the beautiful receiver you see above.
Thanks Stephen. Welcome to the Hall of Fame!
Stephen wrote:
Bill,
Don't worry, you are not alone out there.
Here is my build; sorry that the front panel is overexposed and hard to see, but it is plywood.
I did follow the schematic but due to the contents of the junk box there have been some component changes.
The only thing that I had to buy was the 3/16 x 50 mm (2 inch) brass screw.
My calculations for the coils for the PTO and BPF were a little bit off necessitating padding down the PTO with a further 100 pF (easier than remaking the coil and mounting) and removing a few turns from the T50-6 toroids.
Like other people have found: the audio takes off at full volume; I am thinking but not yet tried adding decoupling between R5 (15K) and C2(47 uF). It isn't the actual values of the electros as I had to use 100 uF so might be the audio output getting back into the earlier stage.
The tuning range I get is our 7000 to 7200 KHz and some shortwave stations above and below, Turning the screw is a little bit fiddly, but once tuned the vfo is quite stable and the audio sounds good.
Best wishes,
Stephen
VK2BLQ
MIT's Haystack Observatory and Dr. Herb Weiss
We are really privileged to have among us (and in the SolderSmoke Direct Conversion Hall of Fame) Phil Erickson W1PJE. Phil is the Director of the MIT Haystack Observatory.
Phil writes:
Hi Bill, Dean, and Pete,
I surfed over today to Soldersmoke and noticed you had put up a very nice film from the 1960s made by MIT "Science Reporter" on the DSKY design for the Apollo Guidance Computer.
In the same vein, you might enjoy viewing something from the same era on the Haystack 37m telescope / radar in its early mid 1960s days:
The video features Dr. Herb Weiss who is still with us at nearly 106 years old (he visited a couple years ago).
Herb built the observatory for its original ballistic missile radar / satellite imaging mission and was involved in early MIT microwave radar development.
"Growing up in Elizabeth, New Jersey, Herb liked gadgetry. As a teenager, he became a ham radio operator and built a primitive television set at the same time NBC was trying to get its first signal on the air. His shop teacher was so impressed by Herb’s genius that he contacted MIT, which invited Herb to attend the college.
He spent the bulk of his career developing radar when there was none in the United States. He joined the Radiation Lab at MIT, which was just being established to support the war effort during World War II, designing radars for ships and aircraft. In 1942, when England was in the throes of its air war with the Nazis, Herb went to England and installed radar in planes with a novel navigation system that he and a team had designed for the Royal Air Force. He later spent three years at the Los Alamos, New Mexico, laboratory improving instruments for the A-bomb. After seeing the need for a continental defense network against the Soviet missile threat, he returned to MIT to build it. If not for Herb, there also likely would be no MIT Haystack Observatory, a pioneering radio science and research facility."
As you can see from above, Herb is also a ham:
"Weiss:
Okay. I was born in New Jersey, and my first acquaintance with electronics was about the age of 12 or 13. We had a battery-operated radio, which didn't work, and I asked around about what do we do about it. They referred me to a man two blocks away, who was a radio ham it turned out. So I carried this monster with the big horn and, I guess, the dog sitting on the speaker to his house. We went down in the basement, and I was just fascinated. I was hooked right then and there. A year later I became a radio ham at the age of 13, 14 and literally have been in the field ever since, until I retired. I was fortunate enough to go to MIT as an undergraduate, and most of the people I ran into of that vintage didn't really have a hands-on feeling for electronics. By the time I got to MIT, I had built all kinds of things, including a TV set. Then it turned out that NBC was just trying to get their TV set on the air in New York on top of the Empire State Building."
https://ethw.org/Oral-History:
--
Herb and his wife Ruth had another career after MIT as a wind power pioneer and he is still an avid sailor:
One of our inspirations, and it came from building ham radio sets as a youngster. Enjoy the history.
73
Phil W1PJE
----
Phil Erickson
Phil Erickson
-------------------------------------------------
I would really like to get more info on Herb's homebrew TV receiver. His was significantly earlier than the one described by Jean Shepherd.
Thanks Phil! And thanks Herb!
Paul 9V1/KM7ABZ's FB SINGAPORE SolderSmoke Direct Conversion Receiver
Wow, I had been feeling a bit discourged about the slow-down in receiver completions, then I woke up this morning and found this e-mail from Singapore. My faith in ham radio was restored. Welcome to the Hall of Fame Paul. You get extra credit for doing it from far-off and exotic Singapore.
Paul includes in his "proof of life" video not only some Malaysian SSB and some CW, but also some very close-by China Radio International. FB Paul.
I also liked the way Paul used the local library to burn the schematic of the receiver burned into the board upon which it was placed. And the library also 3D printed his PTO coil form.
And ET confirmed Proof of Life! FB!
Be sure to check out the really nice build description in Paul's blog and Github page (links below):
Paul writes:
Hi Bill, Pete, and Dean,
I've finally made a "proof of life" video for you, plucking some CW, voice and shortwave signals from the 40 and 41m bands here in Singapore. What fun this was, and I am amazed at how well this works, even from the confines of my 15th floor apartment.
Thank you so much for laying down the challenge - it came at just the right time for me, rekindling my enthusiasm and electronics and radio. It even encouraged me to finally get my license - I'm newly minted general class KM7ABZ (yet to get a 9V1 conversion license for my home here in Singapore). I can honestly say that listening to the SolderSmoke and Ham Radio Workbench podcasts since 2018 or so was worth *at least* 50% on the exam... somehow I already knew a bunch of stuff by pure osmosis!
Everything went pretty smoothly with the build. The only real issue I had was adding some caps to tame persistent motor-boating in the audio amp. Other than that, the build follows the official SolderSmoke schematic and parts selections.
I used the laser cutters at our local library to cut and etch a custom base. The library is a great resource: it’s also where I printed the PTO former.
To get on the air from my apartment in Singapore, I’m using an MLA-30 Active Loop antenna, with a PLJ-1601 frequency counter attached to the PTO to take some of the guesswork out of tuning.
I used the laser cutters at our local library to cut and etch a custom base. The library is a great resource: it’s also where I printed the PTO former.
To get on the air from my apartment in Singapore, I’m using an MLA-30 Active Loop antenna, with a PLJ-1601 frequency counter attached to the PTO to take some of the guesswork out of tuning.
All the details of my build are published at https://leap.tardate.com/
Cheers,
Paul
KM7ABZ from 9V1 land______________________________
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Documentation on Hackaday:
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Thursday, May 15, 2025
Wednesday, May 14, 2025
The Computer Hardware of the Apollo Program
Watching this, it seems like a miracle that we made it to the moon. Some of this construction is downright scary. Sometimes soldering is not good enough -- so they weld. Other times they don't even solder -- they wire wrap! Even in 1965, the wiring of the memory modules was so complex that it was beyond human comprehension. All of this brought back memories of that wonderful book "Sunburst and Luminary" by Don Eyles. I have hopes that he will appear in the MIT video about landing on the moon. Don worked on those programs.
Tuesday, May 13, 2025
On the importance of taking a break.
Thomas K4SWL has a good post about the importance of taking a break from radio. Following up on this, I noted that "taking a break" is often a good way of finding a solution to a difficult problem. I noted that I have confirmed this -- it has worked for me. Pete Juliano N6QW recently announced that he is taking a break from the MHST project. That is a good idea. A solution will likely emerge.
I noted that there is some evidence backing up our suspicion about the benefits of breaks. I earlier shared some comments from Harry Cliff's excellent book, "How to make an Apple Pie from Scratch."
https://soldersmoke.blogspot.com/2024/04/cloud-chamber-finale.html
Harry also wrote about the usefullness of taking breaks. In 1917 Ernest Rutherford was having trouble understanding the presence of some hydrogen nuclei. Harry writes:
"Again, he was forced to put his work on hiatus to go on a mission to the United States in the summer of 1917, but it turned out to be one of those useful breaks when stepping away from a problem lets your mind slowly work out the problem in the background. When Rutherford got back to the lab in September he had the answer..."
There are many other examples.
So, if you get stuck, take a break!
Sunday, May 11, 2025
Peter Parker VK3YE finds a Homebrew Double Sideband Transceiver at an Australian Hamfest
Peter's detective work on the mystery box starts at around 13 minutes into this video. He quickly found a balanced modulator and did not find a crystal filter. This led him to correctly suspect a double sideband transceiver. A look at the LP filter and the VFO led him to suspect a 160 meter rig. Nice work Peter. That's what it is: a 160 meter DSB transceiver.
I had a similar experience with a direct conversion receiver, but never with a full double sideband transciever. Nice find. Peter should try to bring that rig back to life, and he should try to find out who built it.
The Solid State Basics book by DeMaw and Rusgrove looks good. I hadn't seen that one, but I will get one.
Thanks Peter!
Friday, May 9, 2025
Doug AA0MS's FB SolderSmoke Direct Conversion Receiver: "This project has been a hoot!"
Doug built a really beautiful receiver, but reception was marred by a bad hum. It was quickly determined that this was caused by a noisy "wall wart" located close by. A re-location of the power supply remedied that, and allowed Doug to pull in some really nice signals.
Doug writes:
Had a lot of fun doing this over the past couple of weeks. Not my first DC receiver build--I built a Neophyte Receiver from QST years ago--but this one was the most fun. Thanks Bill, Dean, and the whole DCR challenge community--I'm learning a lot in my old age!
I'm a retired pastor who's been fiddling with radio stuff since about 1991, and though I've been inactive for long periods of time, I've always enjoyed QRP and homebrewing (and I've built a bunch of kits, too, including my main rig, an Elecraft K2). It's been a while since I had a halfway decent antenna up, but that's in the works. As a boy I was at my dad's side in his modest shack whenever he was building or operating (he was K8LZO back in the day), and one day while listening to shortwave broadcasts during the first Gulf war, I tuned around and heard some CW signals and decided it was time to learn the code and get my license. Anyway, this project has been a hoot, and I so appreciate all of you and your generosity with your experiences and experiments and successes and failures. Thanks! 73, Doug, AA0MS
Congratulations Doug and welcome to the Hall of Fame.
------------------------------
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Documentation on Hackaday:
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SolderSmoke YouTube channel:
Ramakrishnan VU2JXN's FB SolderSmoke Direct Conversion Receiver: "Extremely thrilled! Hooked!"
This is a really important Hall of Fame entry for us. This is our first completed SolderSmoke Direct Conversion Receiver from India (more will come).
Most importantly, this receiver was built by our good friend Ramakrishnan VU2JXN (ex VU3RDD). Ramakrishnan goes way back in SolderSmoke history. He was the one who first suggested (in 2006!) that our podcast needed a blog to go with it. This was the origin of the SolderSmoke Daily News. A short time later we announced the birth of Ramakrishnan's daughter. That same daughter now has her ham license and will build a second receiver with her dad.
Ramakrishnan VU2JXN
The roots of this receiver are deep in India. When Dean and I first went to the local high school to talk about ham radio support, I carried with me a Direct Conversion Receiver inspired by Farhan VU2ESE. In fact, that receiver had a picture of Farhan and quotes from him taped to the wooden base. When Dean and I designed the receiver that we tried to build with the High School kids, we used an oscillator based on the DC receiver that Farhan was building with youngsters at Indian girl's schools. That is the receiver design that we are using in this SolderSmoke Challenge.
Ramakrishnan is in Bangalore now, which is where he built this receiver. Ashish N6ASD is also there now, and is building a receiver.
Ramakrishnan writes:
This morning before I got ready to come to work, I got a few minutes
to turn on the radio and catch the morning nets. Extremely thrilled to
get this working. The PTO is very stable.
Needless to say, you folks convinced me to get back into homebrew
and you have hooked me into it with this project.
I am off to my ailing mother's place tonight. I don't have a station
there, but I am carrying a copyof EMRFD with me (I have two!).
I want to listen with this receiver as you all always say
and make simple modification to this receiver and improve it.
Again, couldn't turn off from it even though I am at work! The bug has
caught me.
Here is some more video of Ramakrishnan's receiver:
Congratulations Ramakrishnan. Welcome to the Hall of Fame!
--------------------------------
Join the discussion - SolderSmoke Discord Server:
Documentation on Hackaday:
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SolderSmoke YouTube channel:
Thursday, May 8, 2025
Wow! DOVAD and Doppler at White Sands Missile Range
EI7GL has a really interesting blog post about a VHF system used at White Sands to accurately track early rocket tests: https://ei7gl.blogspot.com/2025/05/369-mhz-doppler-radar-antenna-at-white.html
He has nice picture of the antenna. The plaque has the interesting info:
The plaque on display reads as follows...
"36.9 Megahertz Helix Antenna Doppler Velocity and Position (DOVAP)
Reference Transmitter Antenna
Developed during World War II by the Germans as part of a V-2 guidance and control system, DOVAP traced the course of a rocket using the Doppler Effect caused by a target moving relative to a ground transmitter and receiving stations.
Unlike radar, Dovap did not allow scientists to "see" the rocket on a screen. Instead, it sent up radio waves, which were received and rebroadcast back to earth by the rocket. The returned waves combined with the original ground broadcast and produced a musical tone which varied with the rocket's speed - the faster the rocket, the higher the pitch.
DOVAP data was extremely accurate: it could place a rocket's position at 100 miles up within 50 feet. It could collect data at the extreme altitudes of 100 to 300 miles. Dovap's disadvantage was that it took 3 to 4 weeks to reduce the data.
The antenna is a helix because of its physical and electronic characteristics. A helix is simple to construct and operate, provides necessary signal gain and directivity, and can be operated in several modes or polarizations.
The DOVAP system provided trajectory data and ground guidance for most of the early rocket systems: Corporal, Sergeant, Honest John, Little John, Redstone, and Aerobee Upper Atmosphere programs.
This particular antenna was built in the mid-1960s near C Station. Like much of the early instrumentation used here, it was designed and built at White Sands Missile Range.
Erected by White Sands Missile Range Museum. (Marker Number 06.099.)"
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