Just go to http://soldersmoke.com. On that archive page, just click on the blue hyperlinks and your audio player should play that episode.
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Opening: Travel notes: Pete to Denver. Dean to Alaska. Bill in the Dominican Republic.
The future of the podcast. We will embrace our NIMCEL status and fight on in spite of the AI Apocalypse. Thanks to Peter VK3TPM, Hamilton KD0FNR, Sam AI7PR, Todd K7TFC and the WayBackMachine for providing backup and transfer options for the blog. Google could end Blogspot at any time.
Dean and Bill win the 2025 ARRL Technical Service Award. Thanks to Bruce KC1FSZ for the nomination. And thanks to Bill Morine N2COP for letting us know. 91 receivers completed so far!
SolderSmoke East was pleased to host Phil W1PJE, a distinguished MIT radio astronomer AND member of the SolderSmoke Direct Conversion Receiver Hall of Fame.
Dean: Amplifier design, woes, triumphs, tribal knowledge. And help from Claude.
-- Eleven contacts on 40 with the DC RX and a Tuna Tin 2. Mike Bryce WB8VGE came back to my CQ! First ever QSO with SolderSmoke DC receivers on both sides: K1OA-N2CQR.
-- Do real hams use ALC? Do we really NEED ALC?
Mailbag:
Who is the Project 326 Guy? A British engineer resident in China for last 20 years.
Steve EI5DD Ham Radio Ireland magazine. Hey -- Why no Irish DC RX builders?
Mike EIOCL -- Always great to talk on the air with an old friend.
Walter KA4KXX -- I checked into the Sunrise net! With my HW-101! Thanks Walter.
Farhan VU2ESE -- Watched our interview with Phil W1PJE
Phil W1PJE was an SWL with an old Halli receiver. VOA? Boo! But Radio Marti is BACK! Also, the hydrogen line from the cosmic dark ages has red shifted to... 7.1 MEGA hertz! So LISTEN UP!
Phil W1PJE with a Halli and the Haystack Observatory Dome
We were very pleased that Phil W1PJE was able to visit yesterday. Phil is the Director of MIT's Haystack Observatory. He is very knowledgeable on topics related to space and space technology. He is also a member of the SolderSmoke Direct Conversion Receiver Hall of Fame. We talked about the history of the Haystack Observatory, famous antennas (dishes), and about the SolderSmoke Direct Conversion receiver project. It was a lot of fun talking to Phil. We managed to shoot this video with him. Thanks Phil and thanks Dean.
At around 0630 EDT on June 7, 2025 I heard K1OA calling CQ on 7030 kHz CW. This was exactly where I had a crystal. I called him, but he didn't hear me. I sent him an e-mail. We tried again -- he heard me calling him and I heard him responding by calling me, but I don't think we succeeded in exchanging signal reports. It was close, but no cigar.
I had to walk the dog. Scott and I agreed to meet on 7030 kHz at 0730 EDT. Arggh. There was a QSO there. I thought we might have to try to change frequency, but this would have been tough because both of us were crystal controlled on transmit. Fortunately, the contact on 7030 kHz wrapped up. Scott called me, I responded, and we were able to exchange signal reports. I was so excited that I almost forgot to hit the record button on my phone. But I caught the last minute or so. See above.
This was really something. This really goes to prove what Dean and I have been saying all along: this receiver is not a toy! It can be used for real ham radio contacts. And now we have had these receivers on both ends of a contact. For transmit, Scott was using a KA4KXX transmitter with about 3 watts output. I was on my Tuna Tin 2 at about half a watt output.
Quote from the Old Miltary Radio Net: "Being on the leading edge is great, but sometimes being on the trailing edge is more fun." Indeed.
Heard from an Australian on the Southern Cross Net: "My antenna needs a lot of Viagra!"
News from Dayton/Xenia/FDIM: Dayton Xenia. Again, we didn't go. But Bob Crane W8SX was there and got a nice interview with Grayson, Hans, and Farhan. We are presenting these and more. Michigan Mighty Mite Revival at FDIM! Jeff W9TH.
Farhan's review of Hollow State Design:I am compelled to set aside the future of my family and to orphan my cats to resume work on the 250v power supply that I built last year. Inshallah, Allah favors those who favor thermatrons! Grayson's book is imbued with deep experimental insights and littered with gems. You have to read it over and over to find new things each time. It goes into my reference shelf in the lab." Buy it here:https://www.ermag.com/product-category/books/
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PETE'S BENCH:
Pete working on JF3HZB dial. Send Pete a Heath mono-bander!
Indian hams working DC RX. VU2JXN Ramakrishnan, VU2TUM Puneit Singh, Ashish N5ASD, building one in Bangalore with 3D printed form from Scott, KQ4AOP. Ramakrishnan is planning on building a second receiver with his daughter. On June 22, 2008 in SolderSmoke #86 we reported on the birth of Ramakrishnan's daughter. This is that same daughter! See:https://soldersmoke.blogspot.com/2024/01/long-time-soldersmoke-supporter.htmlHow to get a PTO form in India. A tip from Ramakrishnan: "I got the 3d printing done via https://robu.in with 1:1 size. After uploading the stl, I received it by post in 5 days or so."
German students of Andreas DL1AJG. and Canadian students of Daniel VE5DLD.
Receiver built in Singapore! 9V1/KM7ABZ
John M0XJA reports 8 members of his club are building this receiver.
Chuck N4AVC got his PTO coil form 3D printed at the local library. For free! FB!
Few admit to being fooled by April Fool story. But still, inspirational. VK3HN was going for a few seconds -- SOTA AI chatbots? John West liked the 85th harmonic threat.
What next after DC RX? Choose carefully! Don't bite off more than you can chew.
Do some mods! Build something else! And remember to be a homebrew Elmer. Help someone else build the receiver.
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SHAMELESS COMMERCE DIVISION:
Check out the SolderSmoke blog on the WayBack Machine. The blog, not the podcast. www.soldersmoke.blogspot.com Would this be a useful backup if Google were to pull the plug on blogspot? Is the format OK? Is the template recoverable? How best should we backup the SolderSmoke blog?
Be a Patreon SolderSmoke Sponsor! Please subscribe to the YouTube channel! Buy your Amazon stuff through our link. Buy stuff from Mostly DIY RF.
-- Adam N0ZIB Heard my 10 meter beacon from the DR. 28,233.5 MHz On now.
-- Rick N3FJZ Great memory Direct Conversion messages.
-- John KN6FVK had fun with DC RX. Tattoos on Board. We need a high sign! Like the Little Rascals.
-- Adrian M7EFO DC RX builder in GQRP. FB.
-- Steve KW4H Kits not the same as homebrew, but old Boatanchor kits have value.
-- Mike WU2D -- Old buddy Charles Kitchen SK.
-- Craig -- Some really nice feedback on Hack-A-Day re DC RX and Dean's videos.
-- Peter VK3TPM proposes a certificate for SolderSmoke DC RX Honor Roll.
-- Michael WN2A used a 3 inch reflector from Northern New Jersey. Edmunds Scientific "Space Conqueror"
-- Phil W1PJE and Mike WN2A lament that our eyes don't pick up radio frequencies. This would be a great troubleshooting tool! I can SEE the IMD! Perhaps some tin foil hats?
-- John WPE9IRS SW listener! Heard my beacon. Many SWLs switching to tuning in ham stations.
-- Peter VK3YE found a homebrew 160 meter double-sideband transciever at a hamfest. He also found "Solid State Basics for the Radio Amateur -- A QST Anthology" NOT SSDRA. But good!
-- Peter VK2EMU From the Southern Cross (I took a picture of it in the DR!) Building the DC RX!
Andreas DL1AJG was another of those intrepid hams who, in the dark of winter 2023 took up the SolderSmoke Direct Conversion Receiver Challenge in order to test our receiver (before we pushed high school kids to build it). Andreas came to the task with a lot of useful teaching experience. At the time he was an academic biologist and had been teaching a course called "Applied Electronics for Biologists." See:
I put these receivers in the "Honorable Mention" category only because they deviated a bit from the basic schematic: they used an indoor ferrite antenna, had an RF amplifier ahead of the mixer, and did not use a transformer in the AF amp. But they are very clearly the SolderSmoke DC receiver, they succeeded in inhaling RF, and Andreas and his students built them to help us.
Here is the schematic they used:
Click on the image for a better view
Here is an e-mail exchange I had with Andreas when the scholatic dust had settled in June 2023:
Dear Bill,
Please my apologies for my late update on our DCR project. We started with the course in the semester break and once the semester started only a handful of students were able to finish their receiver. A long shelf of shame ....
Here is what we've got so far (those were finished at the end of April already). 3 nice DCRs completely sufficient to copy CW indoors without additional antennas starting from late afternoon. Strong stations can be heard all day. I found that coupling some 6m of wire with one or two windings to the ferrite core can boost the signal dramatically but can also increase noise.
The PTO is based on your design (Bill Meara N26QR & Dean KK4DAS) which was sparked by Farhan (VU2ESE) , except that I've swapped the FET for a NPN. The input amplifier and antenna is from the JUMA active ferrite antenna by Matti Hohtola (OH7SV), the band pass filter is from Hans Summers (G0UPL), the mixer and the headphone amplifier is inspired by Pete Juliano (N6QW), you told me that the diplexer (as well as the whole DCR idea) is attributed to Wes Hayward (W7ZOI) and the perfect schematics of Rick Scott (N3FJZ) where crucial to get me started in the first place. I enjoy keeping track of original sources, as I would do in science. This shows that even little achievements are based on the ideas of many other great people - and this is nothing to be ashamed of.
This was a lot of fun! Thank You!
Best and yours sincerely,
Andreas
Wow, the direct conversion re-engineering of education continues, this time at graduate-school level with biologists in Munich! Amazing.
Andreas points out that his group was also plagued by semester-related problems that caused many additions to the German shelf of shame. Let's hope that someday soon these builders will come to their senses and join the ranks of those who have finished their homebrew projects.
Looking at the schematic (above) of Andreas's project, there are a couple of significant differences from ours:
-- Their AF amp used a transformer-less push-pull design. We had considered this but abandoned it thinking that it would be too complicated to explain the workings of this circuit to our students.
-- Most significant, is Andreas's use of a ferrite rod antenna and an RF amplifier. I think a simple 33 foot quarter wave antenna (with a ground or a counterpoise) might work better. But hey, to each his own! The important thing is that a number of these receivers were successfully built. They look beautiful.
Congratulations to Andreas and the successful Munich homebrewers!
-----------------------------------
Thanks to Andreas DL1AJG. Welcome to the Hall of Fame.
Lot of success! So far 22 completed receivers: 35 others are being built.200 or so people are on the Discord server.
What a great achievement this is! Folks are homebrewing receivers.
Scott KQ4AOP heard his very first amateur radio signals through this receiver. FB!
Lots of great ham homebrew spirit. NE3U, N9TD and others 3d printing coil forms for others. FB
It is not too late. Dean's videos and the Discord server will remain up, even when we ourselves have moved on.
Big Picture: Farhan's Four Stages -- All you need to build a rig: Oscillator, Filter, Mixer, Amplifier.
Homebrew and Manhattan vs. Kit built with PC board. We think Homebrew is a better experience. Dean recently assembled some Ikea kit furniture. Does that make him a carpenter? No.
We do update the schematic as we learn. This is similar to what happens to software. Github? Version 2.3? In the old days, when QST came once a month, we lived a harder life. We don't have to do that anymore.
Let's talk about the boards one by one:
The Oscillator (VFO or PTO):
-- Started out as an amalgam of Farhan circuits: We liked the very simple oscillator he used in his Hyderabad DC receiver project for the girls schools. No need for a hard-to-find variable cap. But we found we needed a 3.3 k ohm resistor in the emitter to make it go. We took the buffer/amp from Farhan's "Daylight Again" circuit, but later (much later!) added a .1uF cap across the source of the J-310.
-- With brass screw, not really a permeability tuned oscillator. Brass has same permeability as air. Works via Eddy currents. But the screw thing is very reminiscent of the old Collins PTOs, so we call it a PTO. And it IS s PTO if you used a steel screw. You should study the doc in the mods section about how to modify the PTO. Metalurgy matters!
-- We used silver mica caps in the frequency determining circuits. This is important.
The Mixer:
-- We started with a simple two diode, single transformer singly balanced mixer. Only LO signal would be balanced out. This would work, but we got a lot of AM breakthrough from Radio Marti, just above the 40 meter band. So we went with a homebrew diode ring mixer.
-- Important to unserstand how the diode ring really works: LO just switches on and off the diodes. Very cool that several builders sought to understand how diode ring works.
-- Best way to test the PTO and the Mixer? Put them together and look at the waveform at the mixer input. Is it flat topping? Then both stages are working.
-- Diplexer: From QRP legend W7EL's Optimized QRP transceiver. Seemed to help knock down Radio Marti. But we kind of knowingly disregarded AF amp input impedance. It would have been too complex to fix. We were going for simplicity.
BP Filter:
-- We actually got to do the NanoVNA test with one set of the high school students. This was very cool. Proves the worth of the NanoVNA.
-- Again good to learn the theory.
AF Amp:
-- Kind of an amalgam of a Forest Mims amp and the amp from the Herring Aid 5.
-- Sure, an LM386 would have been simpler. But we did not want to use ICs. And IC AF amps oscillate too. You learn more by going discrete.
-- We used a transformer. For simplicity. We know the push-pull circuit, but wanted to avoid it. Some guys are going to other AF amp circuits becasue of the transformer. See this as an interim measure... You can fully meet the challenge later, when you get the transformer.
-- We also -- in the name of simplicity -- did not use feedback amps. We have an optional bandaid resistor across the oscillator to lower overall gain.
-- It can oscillate. But keeping leads short, keeping inputs away from outputs, putting adequate electolytics on the 12V power rail can prevent this. This is a good lesson in good construction practices. And with the real world of amplifiers (they all aspire to be oscillators!)
-------------------
Some Tales of Woe:
Simple mis-wiring – need to learn to read schematics
Transistors in backwards – importance of checking the data sheet for your brand – sometimes different brands of same part have different pinouts
Lying Test Equipment
Jay W3V3 unreliable measurements from old Fluke auto-ranging multimemter
Phil, W1PJE – using a 10X probe with scope termination set to 50 ohms
Peter, VK3TPM – faulty component tester (mixed up collector and emitter on NPN transistor)
And many, many setup issues with scopes, signal generators, TinySAs, NanoVNAs
Bad parts
Some “lessons learned” taken from the Walk of Fame Channel
Wayde, VA3NCA – taking care when choosing junque drawer components, solidifying concepts introduce in the licensing material – benefit of hand-son experience “building them made them more real”
Peter VK3TPM – don’t trust your transistor tester, transistors can pass signals even when wired backwards. Importance of 10X probles. NP0/C0G caps for frequency stability
Ken, W4KAC – learned to better use his test equipment to trouble-shoot, and finally learning to trust his troubleshooting after changing out a faulty transistor.
Parts sourcing: We were surprised at how much time people spent on this. Parts sourcing struggle reminds us of the importance of 1) understanding the circuit and 2) having a decent junkbox. 3) scrounging old parts when necessary.
Looking ahead: Antennas are important! You probably can use Cat 5 cable instead of real coax. Noise is natural. Mods are fun. CW in some ways harder than DSB. Lot of antenna info on the internet.
You can modify the PTO for easier tuning. See the doc. Add a front panel, or a case. Once your basic receiver is done, you can experiment with better circuits. See the mods doc for ideas.
Final Comments:
-- It is ultimately the builder who has to make the machine work. Homebrew means that YOU the builder are going to make it work.
-- Be careful about who you take advice from or give advice to. Don't be afraid to say "I don't know." Ask yourself: Is the guy who is giving me advice really an experienced homebrewer? Am I?
-- We learned a lot in this process. You guys have made this a better receiver.
-- Be careful about starting over... Bill and Dean's homebrew nightmare!
SolderSmoke Challenge – Direct Conversion Receiver – the Audio Amplifier Build and Receiver Demonstration
In this episode Dean, KK4DAS wraps up the initial build of the SolderSmoke Challenge DCR. He takes us through the audio amplifier stage and demonstrates the newly built receiver just moments after connecting the audio module to the mixer and hooking up a speaker. The audio module is conceptually simple – three nearly identical stock-standard common emitter audio amplifiers which provide the 80-100 dB of amplification you need to go from microvolts of RF to volts of audio to drive a speaker. The challenge with all that amplification in a small board is to keep it amplifying but to stop it from oscillating and as you’ll see in the video, good construction technique is critical to good performance.
And wow! We now have more than 30 builders working on the SolderSmoke Challenge, with more builders completing the challenge every day. And those are just the ones who are active on tour Discord server. If you have completed the DCR or even if you have just started building it, we want to hear from you. Send a picture or better yet a video – make it a selfie and you can join the SolderSmoke challenge hall of fame!
And if you are not yet building it, you must ask yourself one question:
Dean will soon post his longer video on how to build the fourth and final board of the SolderSmoke Direct Conversion Challenge receiver, but we know many builders are chomping at the bit, and are going ahead with the building of the AF amp board. We hope that this short preliminary video will help. Here Dean descibes the benefit of building the three stage amp, ONE STAGE AT A TIME.
Response to the challenge has been great. There are at least 30 receivers under construction around the world. Many are already inhaling RF. All of the problems that arise with true homebrew are being identified and fixed.
Dean's full AF amp video will be out shortly. Thanks Dean!
The SolderSmoke DCR challenge is going well. Our Discord server is bustling with activity and we are impressed that several intrepid homebrewers have already completed the receiver. So, we know that you can too! In this episode Dean, KK4DAS walks us through the design and construction of third of our four boards, the 40-meter band pass filter. The band pass filter ensures that the only signals that get through the receiver to the speaker are those that are in the 40-meter band. Dean also gives an update on the Challenge and discusses some recent improvements we've made to the circuits based on feedback from our builders.
Dean now has the PTO, the Diode Ring, and now the 40 meter bandpass filter. Dean fires up his signal generator and, using his 'scope we see audio coming out of the mixer. FB.
Dean says he will have the complete build video for this stage soon. Thanks Dean.
SolderSmoke Challenge – Direct Conversion Receiver – the Mixer
The mixer is the heart of the direct conversion receiver. It’s the circuit that makes a receiver a receiver. It takes the RF from the antenna and mixes it with the local oscillator to extract the audio. In this video, Dean, KK4DAS walks us through the design, build and testing of the double balanced diode ring mixer we chose for the SolderSmoke Challenge DCR. He also explores some of the myths, legends, and lore around mixer design. If you are not yet convinced, we can make an effective receiver with just four simple boards you definitely want to watch this vido to the end. Mixers have been a passion (some say obsession) of mine for a long time. If you search for “mixer” on the SolderSmoke blog you will find many postings over the years. Whenever I want to learn more about some RF circuit or other I always turn to Alan Wolke, W2AEW’s excellent YouTube video series. In the video linked below Alan does an excellent job of explaining mixer theory and demonstrating how the switching action of the diodes produces the sum and difference frequencies.
Related links:
Alan Wolke, W2AEW - YouTube Video #167:
How a Diode Ring Mixer works | Mixer operation theory and measurement
The DCR challenge is going well, and we have several builders making good progress. We noticed that some first-time builders are having a little trouble with soldering. Cold or weak solder joints are the bane of the of the homebrew builder’s existence. It happens to all of us. A board that was working fine suddenly is not working – you poke around and touch some part and the board springs to life – you just found a cold solder joint. Dean, KK4DAS put together a short bonus video just on soldering. He covers the tools you need for a basic soldering station, and step-by-step instructions for reliable soldering Manhattan Style.
The response to the SolderSmoke DCR challenge has been terrific -with nearly 7,000 views of the first episode! Thanks so much for checking it out. The goal is to convince you that you can build your own receiver and then go get you started on Homebrew ham radio. We already have confirmation that it can be done! Congratulations to Peter, VK3PTM and Matthew, KY4EOD who have both completed the receiver. The boards look good and, even better, they sound great. Videos and descriptions are here on the blog and on the SolderSmoke Discord sever. Speaking of the Discord server, we already have a very robust conversation going, It’s a great place to give feedback and to get your questions answered. Builders are helping builders and we at SolderSmoke are trying to answer as many of your questions as we can. This is a beginner’s project, so all are welcome.
In episode 2 of the SolderSmoke Direct Conversion Receiver challenge we tackle the PTO. We discuss a bit of the theory, walk through the schematic, and take you step-by-step through building and testing the oscillator and buffert. By the time we are done we will have achieved JOO! (the Joy of Oscillation). And when you build it you will be 1/4th of the way to having build your own 40 meter receiver.
"SolderSmoke -- Global Adventures in Wireless Electronics" is now available as an e-book for Amazon's Kindle.
Here's the site:
http://www.amazon.com/dp/B004V9FIVW
Bill's OTHER Book (Warning: Not About Radio)
Click on the image to learn more
Where are the readers of SolderSmoke Daily News?
Pete Juliano N6QW
Master Homebrewer
Dean Souleles KK4DAS
With beret and with a Michigan Mighty Mite in hand
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