"The Magic That Only Comes from a Radio you Built Yourself" -- The Many Benefits of True Homebrew

 Receiver on the bottom,built around 1997. 

Transmitter upper right, built in 1993. Power supply upper left, 1998.  

Adventures on the road to HB

Homebrew Radios in the age of the Internet

By Bill Meara, N2CQR

MAGIC

"I listened to the magic that only comes from a radio that you built yourself." In that one sentence (posted to an Internet e-mail group), Mike, VE2GFU, nicely described the feeling that can arise in the midst of a room full of solder smoke... and the reward that awaits those who endeavor to build their own radio receivers. In an age of mass produced, homogenized, high price commercial equipment, there is still magic to be found in the production and use of simple homebrew radios. I recently put together my first superhetrodyne communications receiver - I had so much fun with it that I thought my fellow amateurs might be interested in the project.

I was a frustrated teenage radio builder....

When I put my first homebrew low power transmitter on the air a few years ago, I thought I'd maximized my ham radio satisfaction. I gleefully reported to other stations that "RIG HERE IS HOMEBREW". For a while, I really thought that my fun meter was pegged! But everytime I looked at the commercial receiver that sat alongside my QRP transmitter, I knew in my heart of hearts that I still had some work to do. The truth was that only half my station was homebrew. Until I built my own receiver, I would not be able to enjoy the warm glow of satisfaction that comes from running a completely homebrew station. As a kid, I'd always looked with wonder and envy at the exotic homebrew stations in the DX column of QST magazine. I wanted to do what those intrepid foreigners had done. I decided to finish the job. I decided to build a receiver.

"Receivers are Difficult!!!"

I approached the project with some trepidation. Since my earliest days in the hobby I'd heard that "receivers are difficult." There seemed to be a deeply believed and long-standing bit of conventional wisdom that said that most hams could sucessfully build transmitters, but receivers were somehow beyond our capabilities. During radio club meetings, old timers would share tales of homebrew adventures from days-gone-by. They told of tube transmitters built on chassis fashioned from purloined street signs. There were a lot of great stories, but they were all about transmitters. When I'd ask about receivers, the old timers would look a bit sheepish as they admitted that their receivers were all commercial.

Receivers are difficult. I knew from personal experience that there was some truth in this axiom. As a teenager I had tried to barge into the ranks of the homebrewers with an audacious attempt at reproducing a varactor diode-controlled receiver I'd seen in one of the ham magazines. I never got it to work. As I approached this recent receiver project, I think a desire for vindication - and a desire to finish the job I started in 1974 - was part of my motivation.

Barebones, no frills, one step at a time

The "Barebones Superhet" presented in a July 1982 QST article by Doug DeMaw seemed to be just what I was looking for. As the title imples, it is a very simple, easy-to-understand circuit. Most of the stages were built around discrete solid state components - no mysterious IC black boxes. 

Remembering my bitter defeat in my earlier receiver project, I decided to take a fool-proof approach to this one. I took Doug DeMaw's very simple schematic and made it even simpler by dividing it up into separate stages. I would build each stage one at a time, each on a separate printed circuit (PC) board. For my receiver there would be separate boards for the Radio Frequency Mixer, the Variable Crystal Oscillator (VXO), the intermediate frequency (IF) amplifier, one board for the Product detector/beat frequency oscillator (BFO) and one audio amplifier board. I would test each stage before going on to the next.

Parts acquisition in the age of the Internet

As a teenage wanna-be radio maker, parts acqusition had been a major problem. I'm happy to report that the Internet and Express mail services have largely eliminated the tortuous "waiting for the mailman" vigils that many of us endured back in the dark ages. I kicked off my project with a brief session involving several parts catalogs, my computer and a credit card. A few short days later, the boxes started coming in and actual construction was about to begin.

While the catalog houses provided many of the parts, my junk box, hamfests and fellow hams were the sources for many of the components. I think that this diversity of parts sources adds to the character of the final product. When I look at my receiver, I can see parts that came from my old friend (now SK) Pericle, HI8P. There are components in there that were sent to me by Tom, W1HET and several other ham friends. There is a reduction drive from an old Swan 240 and a grommet from a deceased Heathkit Luchbox. The LM386 audio amplifier chip (a concession to modernity!) came out of a Kanga Kits direct conversion receiver; I didn't have an eight pin socket for it, so I scrounged through my junk box, found a 16 pin socket and cut it in half. Like I said, this approach to parts acquisition gives the radio some character. 

Lunch time PC board design

My "one stage at a time" approach resulted in some special challenges and opportunities. I had to design the PC board patterns myself. For hams accostomed to using ready-made PC boards, or simply reproducing patterns made by others, this might seem like an intimidating task, but since I was dealing with only one stage on each board, it turned out to be easy and rewarding. I was using boards that fit very conveniently in the front pocket of my shirts. I made PC board design a lunch-hour project. I would go to work with my schematic and a couple of index cards in my pocket. I'd cut the cards down to PC board size and used them to plan the layout of the boards. I usually had to do two or three "drafts" before I was satisfied, but I found that I was able to do about one board per lunch hour. Doing the layout myself definitely added to the "I did it myself" feeling at the end of the project.

I set a goal of completing one board per week - most of the design and planning would take place during the lunch hours, most of the construction took place early on Saturday and Sunday mornings.

Testing, testing....

My arsenal of test gear is far from laboratory grade! I have a little (ancient) Eico 435 oscilliscope and an old Heathkit signal generator. I bought the scope for 25 dollars on the Internet. The generator was a 15 dollar hamfest purchase. The 'scope will only read up to about 5 Mhz, but since the IF of my receiver would be 3.579 Mhz, I knew it would be very useful.

Testing the stages was a lot of fun. The VXO and BFO were easy to test - I just listened for the signal on a Radio Shack general coverage receiver. For the IF AMP I used the signal generator to put some 3.579 Mhz energy into board and used the 'scope to make sure it was amplifying.

One of the most difficult parts of HF superhet construction is the IF filter. Doug DeMaw's circuit employed a three crystal ladder filter. Doug described it as simple and easy, but to me it looked a bit intimidating. One of the benefits of homebrewing is that you can really "have it your way". Wishing to avoid a frustrating battle with a complicated filter, I searched through the QRP/Homebrew literature for a simpler approach to IF filtering. I found what I was looking for in another article by DeMaw. In this cicuit he used one crystal with a resistor to ground. I decided to use this simple filter and put off construction of the more sophisticated (and narrow) three crystal circuit until later.

So I redesigned the RF mixer board to accomodate my simplified filter. I wasn't quite sure if this little foray into electrical engineering would be successful (my degree is in economics!) so the testing of this stage was tinged with some anxiety. I set the signal generator for the low end of the 20 meter band. I got the VXO oscillating and put the scope on the output of my simple filter. Slowly I tuned the generator across the 20 meter CW band. All of a sudden, at one very specific point, a big 3.579 Mhz signal popped onto the 'scope screen! Eureka! My mixer was mixing and my filter was filtering!

Holy cow! It really works!

After about a month and a half of this, I had assembled an impressive looking collection of small circuit boards. I couldn't resist putting them all together on the workbench to see if this thing would really receive. Armed with a set of alligator clip test leads I connected inputs to outputs. It was early in the morning and 20 wasn't really open yet, but it was Saturday and I figured there were some folks out there trying to coax the ionosphere into action. As I was checking the test leads, I started to hear - almost imperceptiably at first - CW. At first I thought the sound was coming from my Drake 2-B, but a quick check showed the Drake was completely off. My little creation was actually receiving radio signals!

As late afternoon rolled around I decided to see how my still incomplete device would handle SSB. As luck would have it, my crystal let me tune around 14.200 Mhz. There I found the very melodious tones of EA3OT. Echo Alfa Three Oooold Timer, with his "six over six over six" antenna system filled my shack with beautiful phone signals. My relatively wide, one crystal filter was ideal for reception of Mike's fine signal. There really was something quite magical about looking at my little collection of boards and realizing that they were receiving signals from far-away Barcelona. I was experiencing "the magic that only comes from a receiver that you built yourself..."

Enclosure (sort of)

Now it was time to start putting the radio in a proper enclosure. A few years ago, Paul Carr, N4PC, * (*Described in several editions of the CQ magazine during 1993) built a 40 meter solid state rig on a wooden base. Disliking metal work, I immediately appreciated the wisdom of this approach. Realizing that I'd probably want to add additional circuits later on, I decided to make the chassis about twice the size I really needed. A visit to Home Depot yielded a suitable (16"X11") piece of pine. I also picked up some very light sheet metal that I thought would help with the front panel.

I had three large double sided PC boards in the junk box. The circuit boards were attached to these PC "base" boards with some Radio Shack spacers and 4X40 screws. The Base boards were bolted to the wooden base.

I used the sheet metal to fashon an L shaed front panel. The material was not quite rigid enough, so (in keeping with a very old ham tradition of stealing radio materials frm the kitchen) I put a little "cookie baking sheet" between two layers of the Home Depot sheet metal. The L shaped panel was afixed to the pine base. A smaller L shaped piece of scrap aluminum was attached to the back side of the pine chassis - this would serve as the mounting point for the antenna and power connectors.

My creation was starting to look like a radio. Better yet, it resembled one of those impressive homebuilt rigs that I used to see in the DX column of QST. I felt I was getting close to membership in the that elite group of intrepid hams who had actually "rolled their own." I was starting to feel a kinship with all of those intrepid, creative wackos who build things in their basements or garages. I felt part of the same homebrew tradition that dates from in the early days of ham radio. Just like the guys who build small airplanes in their backyard shops, just like those guys in California's Homebrew Computer Club, I was approaching the point when I could begin sentences with the proud phrase, "I built..."

Debugging

But of course, I was not done yet. Not by a long shot. When you are homebrewing, you have to be patient. You have to start out realizing that you are definitely not involved in "plug and play" radio.  Very few homebrew receivers will work properly the first time you fire them up. The radio needs to be properly aligned. Amplifiers and oscillators need to be tamed. But I think this is one of the most satisfying part of the homebrew experience. It is during this phase that you really get the sensation that you are molding your creation to satisfy your requirements. You are physically molding it by deciding where you want the control knobs and external connectors. And (even better) you are molding it electronically by deciding how you want to to sound. It is during this phase that you really put electronic theory to work.

I had a few very common problems. My audio amplifier would scream like a banshee if I turned the gain up. My variable crystal oscillator was kind of sluggish - it sometimes wouldn't start up right away when I applied power. A preacher from the 22 Meter broadcast band urged me to repent every time fired up my new radio. And worst of all, 80 meter CW signals from the venerable W1AW jumped right over my receiver's front end filters, landing right in my 3.579 Mhz IF frequency. These signals not only appeared to be mocking my technical abilities, but they also seemed to be making fun of my code speed.  Like I said, this was definitely not plug and play.

In my effort to fix these problems, modern technology provided me with resource that was completely unavailable during my earlier (1974) battle with a superhet: the Internet. The 'net puts the radio builder in almost instantaneous contact with a worldwide network of entusiastic solder melters. I found the rec.radio.amateur.homebrew USENET group to be an excellent source of information, advice and moral support.

The internet can turn your homebrew project into a multinational enterprise. Hams from around the world chimed in with helpful hints. It was a lot of fun to encorporate suggestions from distant Australia into my little HB receiver. And it was very reassuring to know that all those far-flung Elmers were available if I got into a real jam.

I was particularly gratified when I got some e-mailed words of encouragement from the guy who had designed the receiver I was building, Doug DeMaw, W1FB. Doug's son had spotted one of my pleas for help in one of the USENET groups and had relayed my message to his father. Doug sent me a very nice and encouraging note. I was saddened to learn that shortly after our exchange he became a silent Key.

Solutions to most of my problems came very quickly - and I learned something with each of them.

The screaming banshee audio amp turned out to be the result of a simple circuit error - I'd failed to ground one of the bypass caps on the LM386 AF amp chip (the only IC in the rig).

The Variable Crystal oscillator was made more obedient by playing a bit with the values of the two capacitors that madeup the feedback network in the Colpitts oscilator.

The preacher and W1AW required a little more effort. I decided that I needed a bit more filtering at the front end of the radio. I could have easily just thrown in one or two more tuned circuits between the antenna and the mixer, but I was concerned that losses in these circuits would adversely affect receiver sensitivity. Roy Lewllan, W7EL, had advised me (via the net) to perform a simple check of receiver sensitivity: I was told to listen to the receiver output while connecting and disconnecting the antenna. If connecting the antenna resulted in a noticeable increase in the noise output of the receiver, there would be no need for additional front end amplification. My receiver was not really doing well on this test, so I was concerned that adding more tuned circuits at the front end would worsen the sensitivity problem. It seemed to me that a stage of RF amplification that included a couple of tuned circuits might help me banish the unwanted preachers and code practice sessions without further degradation of receiver sensitivity.

Doug Demaw's QRP Notebook pointed to a simple, grounded gate FET amplifier with tuned circuits at the input and output. I quickly put this stage together on its own small PC board and put it between my antenna connection and the mixer board. The amp was obviously amplifying, but it seemed to be getting carried away. Whenever I'd tune both the input and output circuits to peak, the amp would begin to oscillate. I turned to the Internet and aske for advice. Help quickly came from afar. A fellow named PK Singh sent me an email with the solution: I had to "tap down" on the toroidal coils in the two tuned circuits. This deliberately introduced impedence mismatches that effectively reduced the stage gain and thus stopped the howling. (A side benefit was a noticeable increase in tuned circuit Q - a big help in my battle with the 22 Meter station). With the tapped down amp in the circuit, my receiver passed Roy Lewellan's noise test with flying colors and I was no longer the subject of harrassment from 22 meters and W1AW. Viva el Internet!

Coffee can frequency readout

My frequency readout scheme needed some work. The tuning capacitor I was using had a little venier reduction drive built into the cap. This made for very smooth tuning, but it made it impossible to work out any kind of frequency readout on the front panel. I had to peer over the panel and look at the variable capacitor to determine where I was in the band. In an age of multidecimal numeric digital readout, I was clearly behind the times.  And my neck was starting to bother me. 

To upgrade, I found a junkbox 365 pf variable cap with no built in reduction drive. This was about twice the capacitance that I needed, so I simply plucked out about half of the rotor plates. I also found a Johnson 6:1 reduction drive in a junker Swan 240 transceiver. With a piece of scrap aluminum, I engineered a little mount for the capacitor. The Johnson drive allows for the attachment of a frequency readout dial. I found that the top of a coffee can (the metal part you always throw away) was ideally sized for my front panel. Soon I had the modified cap, reduction drive and coffee can readout dial mounted on the front panel. A triangular piece of electrical tape provided a sharp looking pointer. A few pieces of masking tape on the coffee can top served as frequency markers. I realize that my "coffee can readout" will seem incredibly crude to those accostomed to glowing numerals, but I get a real kick out of it every time I spin that little homebrew mechanism.

Filter Finale

In a certain sense I was done. I was able to pair my new receiver with my QRP transmitter and was easily able to make QSO's. I was working European stations regularly with 3 watts out. But my simplified crystal filter was a too wide for serious CW work. I could hear several CW signals simultaeously and - worse yet - I could hear the "other sideband" on the stronger signals. So I hadn't really achieved the coveted "single signal reception" status that is - after all - one of the main reasons for going the superhet route.

There are a number of excellent article out there on the design of CW crystal ladder filters. Unfortunately the building of these filters requires the use of some special test gear to determine the electrical charecteristics of the particular crystals that will be used.

Wishing to avoid the construction of test gear that would be more complicated than my radio, I decided to simplify filter construction. I bought a bag of 50 3.579 Mhz TV color burst crystals from Dan's Small parts. I then built a simple Colpitts oscillator circuit on a Radio shack breadboard. I tuned my Drake 2-B receiver to 3.579 Mhz and started plugging crustals into my breadboard oscillator. I screened out those rocks that were signficantly off frequecncy, then I went through the pile again, judging by ear (using the tone from the Drake 2-B) to select three crystals that were very close in frequency. (I know that a frequency counter would have made this easier, but I don't have one so I had to "make do.")

I simply pugged these crystals into the filter circuit described in Doug DeMaw's 1982 article. Essentially I was "hoping for the best", hoping that the characteristics of my rocks would not be significantly different from those employed by Doug DeMaw.

It all worked out very well. The new filter significantly sharpened my receiver's selectivity. I could no longer hear strong signals at two points on the dial. Single signal reception had been acheived!

My filter proved to be far to sharp for confortable SSB reception, so I worked out a little switching arrangment that allowed me to switch between my original (wide) filter and the new, sharp CW filter. MISSION ACCOMPLISHED

I found that my technical skills improved dramatically during the course of this project. I even noticed a marked impovment in manual dexterity. By the time the receiver was finished, I was much more confident about putting together my own circuits. In order to be truly "100 percent homebrew", I needed to whip up a power supply for my station and a sidetone oscillator for my transmitter. These projects were quickly completed and I was soon on the air with a 100 percent HB station.

Homebrew is good for you! It really doesn't matter what band or mode you build for, a homebrew radio will provide a kind of satisfaction unavailable from store-bought units. A project like this will improve your skills, expand your knowledge and will put you in league with all of those intrepid inventors who have turned piles of parts and wires into devices that magically extract signals from the ether.

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More details on this homebrew rig here: https://soldersmoke.blogspot.com/2022/09/fixing-up-old-homebrew-rig-barebones.html

Please Listen for my 10 Meter Beacon! 28.2335 MHz

 

There it is, in all its glory.  The transmitter itself is a Doug DeMaw "Lil' Slugger" CW transmitter for 10 and 15.  I built it, maybe 25 years ago?  Still works.  3 Watts out, crystal controlled on 10.  Antenna is a 1/4 Wave groundplane up about 70 feet.  Mike WN2A kindly made me a PIC-based keyer that is generating the CW -- you can see the keyer board attached to the transmitter.  For the base I used a board and some socketry that had previously held a Ramsey-kit Q-AMP 20.  

I have it hooked up now.  It is transmitting.  Please see if you can hear it.  Send me a report!  The frequency is 28.2335 MHz. The callsign is HI7/N2CQR.  I am in the Dominican Republic. 

SolderSmoke Podcast #255 -- Accept the HB Challenge!, DeMaw SSB, Brilliant TR-3, Tube Talk, Ground Truth, Tales of Woe, SDR RX, Pico Balloons, MAILBAG

Mythbuster II -- 20 meters only

SolderSmoke Podcast #255 is avalable: 

Audio:      http://soldersmoke.com/soldersmoke255.mp3

Video:       https://www.youtube.com/watch?v=c54qiITMxwM

--   First: Happy Holidays!   I have on a Santa Claus hat!  

-- December 18.  Pete completes another orbit.  Happy Birthday Pete.  Please send him birthday greetings. 

 --  Bill was on Ham Radio Workbench: https://soldersmoke.blogspot.com/2024/11/bill-n2cqr-appears-as-guest-on-ham.html  Our challenge to HRWB.  Gauntlet thrown down... OUR CHALLENGE HAS BEEN GRACIOUSLY ACCEPTED!     We now extend the challenge to the entire SolderSmoke community: Build one of these:  https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

Homebrewing is not for the faint of heart!  Accept the challenge!  Build stuff! 

Our question:  Did Doug DeMaw ever build an SSB transceiver?  Starting in September 1985 he wrote a five part series on an SSB TRANSMITTER for QST.  But he prefaces it by asking, "Why would anyone build an SSB transmitter today?" He says it would be fun "for the experience and understanding it would provide." But not for use, you see... And it is not a transceiver. 

Bill's theory about DeMaw, SSB,CW and sideband inversion:  He was a CW guy so sideband inversion did not really matter. He could get it wrong and still make it work.  

Pete's Bench: 

Brilliance and the TR3. https://www.youtube.com/watch?v=2C-eYB8yFzg&t=13s

A tale of woe.  Done in by a light bulb.

Thanksgiving dinner and SSB transceivers. https://n6qw.blogspot.com/2024/11/11292024-how-to-homebrew-thanksgiving.html             https://www.pastapete.com/

Hybrid plans:  https://www.youtube.com/watch?v=zKUjHZMf3Fs&t=5s

Dean's Bench:

Travelogue – Falcon 9 Launch

Building a homebrew T Match tuner for the end-fed long wave – sourcing the parts, winding the coil – taps, testing 

VWS Makers Projects

SDR Receiver Project – starting in January

VWS Pico Balloon – Traquito - Traquito - WSPR Pico Balloon

Revisiting the 10M DSB rig

Soldersmoke listener challenge – build a DCR with KK4DAS – overview then one board a week

SHAMELESS COMMERCE DIVISION:  Mostly DIY RF.    Please subscribe to our YouTube Channel.  And use the Amazon link on our blog.  Become a Patron via Patreon (on the blog). SolderSmoke is now on Blue Sky and Threads -- follow us or at least like us there. Please turn on automatic downloads on your podcast app -- most podcast apps will only store a few episodes. This will help bump the numbers, which will improve visibility.  Please give the show five stars and, if possible, a nice review on your podcast service,  That will help with the discovery rate for people looking for new podcasts.

Bill's Bench:

Is "The Ground" a Myth?   ARRL VP says Ground is a Myth: https://www.youtube.com/watch?v=KdX-978tvkY.  Bill disagrees.  Helicopter story.  Refrigerator story.  Original single wire telegraph system. https://en.wikipedia.org/wiki/Single-wire_earth_return

Front Panel and Freq Counter for the Mythbuster II. 

Another Tale of woe:  A mysterious audio problem on the 15-10 II rig.  Done in by.... Duh!   Comparing sideband suppression with Mythbuster I.  Differences in Hfe?  Notes on Mythbuster II build. 

TinySA Ap -- A cure for Fat Finger Syndrome? : http://athome.kaashoek.com/tinySA/Windows/  How to get and load the Ap (you might want to start watching at 1:11) https://www.youtube.com/watch?v=zu4X5dyUlpo&t=2s  General info video on the TinySA Ultra: https://www.youtube.com/watch?v=6C24RnYNOWQ&t=1143s

For the DR shack -- I got a Swan SWR-1A on E-Bay. 

 MAILBAG:   

-- Scott KQ4AOP trying to track down the DeMaw SSB transceiver mystery.  On the DC Receiver: This was my first receiver build and, it was great fun. When you finish the build and prove you are able to tune through the band, you are welcomed into the secret society! The build is the initiation.I am happy to print and ship the PTO if needed. 

-- Bill WA5DSS has built a High School Direct Conversion Receiver! 

-- Grayson KJ7UM liked the 1971 video on old THERMATRON AM radios: https://soldersmoke.blogspot.com/2024/11/basic-radio-circuitry-1971-film.html

-- Chris KD4PBJ sent nice electronic care package. 

-- Walter KA4KXX is honored that Dean named his dog for him (Walter was just kidding) 

-- Thanks to Bob W8SX for FDIM 2024 interviews.

-- Tony G4WIF insomnia driving him to podcasts.  Amazed by quantity of food eaten on Thanksgiving. 

-- Nice comment from Trigger about the podcast.

-- Clint says "valves" when he means THERMATRONS.   Kindly asks about "Oooo Thats Awesome"

-- Eric 4Z1UG faced with a new challenge.  Get well soon OM.

-- Sam WN5C and his Chat GPT AI Elmer. 

-- Paul VK3HN on using AI for electronic design.  I dunno... Apocalypse Now in the DR?

-- Tommy SA2CLC FB old military gear on QRZ site. Helps with HP8640B repair. 

-- Mike WN2A nice comments on Chappy Happy's FB Tezukuri DC RX https://soldersmoke.blogspot.com/2024/11/tezukuri-and-chappy-happy-amazing.html 

-- Allison KB1GMX.  Good info on ground truth. 

-- Phil W1PJE Had to throw out 15 test leads.  Fake wire!  

--Todd K7TFC Thoughtful comments on AI and ChatGPT, Help with TinySA Ap 

-- Steve KW4H Boatanchor guy.  Likes that we often scratch our heads trying to understand. 

-- Nick M0NTV built a 40 meter DC receiver: https://soldersmoke.blogspot.com/2024/12/a-40-meter-direct-conversion-receiver.html

-- Dave AA0KU asks about CCI amp (AN762)  Also woking on Drakes. 

-- Jack (Dhaka Jack!) F4WEF/AI4SV  Good thoughts on how to bolster SolderSmoke's ratings.

--Tobias thinks the decline IS ALL HIS FAULT!   

-- Tony VE7JUL building a TJ DC RX.  Go Canada! Dean says: 3D print PTO former at 110%

-- Jim KI4THC getting his uBITX on the air. 

10S November 23, 2024 1517Z SV1AER Kostas in Athens.  Said a very sincere “Oh my goodness! Congratulations!  That is not a very common thing!” when I told him rig was homebrewed.  Nice fellow.  Great response. 

Will KI4POV on QSO Today with Eric 4Z1UG

I really liked Eric's interview with Will KI4POV:  

https://www.qsotoday.com/podcasts/KI4POV

Will has appeared on this blog and podcast before: 

https://soldersmoke.blogspot.com/search?q=KI4POV

There were a lot points in Eric's interview with Will that resonated with me: 

-- Will told about how his very understanding and perceptive wife KNOWS when a homebrew project is not going well.  Yea, we have the same situation here!

-- Will mentions the wisdom of Wes Hayward, Doug Demaw, and Pete Juliano.  

-- Eric mentioned that there is a bit of his own blood in most of his homebrew projects. One slip of he screwdriver is often enough.  My projects also often have a bit of my A+ in them.  This adds soul to the new machine. 

-- Will spoke of S-38s and HW-8s.  I have both these devices here with me in the Dominican Republic. I  have used both of them here.

-- Will mentioned the magic that comes when you listen with a receiver you built yourself.  Yes. 

-- NanoVNA.  Yes, very useful.  

Lots more great stuff in this interview.  Thanks Eric and thanks Will. 

Old Tricks, Lore, and Art -- Freezing and Baking our LC VFOs -- An Example from Cuba

Pavel CO7WT explained why Cuban hams used a process of thermal endurance to improved the frequency stability of their homebrew rigs: 

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I'm CO7WT from Cuba, I started my endeavor in ham radio with a islander board.

They (FRC, like ARRL but in Cuba) made a print of a PCB to build the Islander, with component numbers and values, making construction fool proof, I think it was on the 90 or end of the 80...

Mine was built with scraps from an old KRIM 218 Russian B&W TV as Coro's explain, later on I get the 6bz6 and 6be6 tubes for the receiver (this worked better than the Russian parts) the VFO was transistorized, made with Russian components. A friend CO7CO Amaury, explain me a trick: thermal endurance:

For a week put a crust of ice on the VFO board by placing it in a frosty fridge during the night. Put them in the sun by day. This indeed improved stability, this was an old trick.

By thermal endurance I mean improving thermal resistance vs tolerance, meaning that tolerance doesn't vary as much with temperature changes.

 It's crazy, but it worked!!

I remember that my vfo was on 7 MHz, with Russian kt315 as normal Russian transistors and capacitors, nothing 1-5%, 20% at most, it ran several khz in 5-10 min, mounted on a Russian "Formica" board (no PCB) and wired underneath.

After that treatment to the complete board with components and everything, including the variable capacitor; I managed to get it to "only" noticeably in the ear after 30-40 minutes.

To me it was magic!!

Basically, what I'm describing is just "thermal annealing", but Cuban-style and with more extreme limits.

In a refrigerator you could easily reach -10 c and in the sun for a day in Cuba 60-80 celsius at least.

In Cuba in the 1990s-2010s many designs of DSB radios proliferated, both direct conversion and super heterodine (using an intermediate frequency)

At first tubes and then transistors, mostly using salvaged parts, so it was common to find 465/500 kHz (if common Russian) 455 khz and 10.7 Mhz with or without "wide" filters since narrow filters for SSBs were not scarce: they were almost impossible to get.

Not only that, crystals, ifs, PCBs, transistors, etc.

Then, around the 2000s, Russian 500 khz USB filters began to appear (from Polosa, Karat, etc. equipment from companies that deregistered and switched to amateur radio) and that contributed to improving... Even though at 7 MHz 500kc if is very close.

I made many modifications with the years mostly from 1998 to 2004 ish... better filters in front of the first RX stage (same IF described between stages) improved selectivity and out of band rejection, remember we had on that days broadcast as low as 7100 khz

Tx part was a pair of russian 6P7 (eq. RCA 807) in paralell, etc.

The Jagüey and others is one of those evolutions...

 This is something I remember...

73 CO7WT

----------------

This is not as crazy as it sounds.  We can find versions of the same technique in the writings of Roy Lewellan W7EL, Doug DeMaw W1FB, and Wes Hayward W7ZOI.  I found this 2007 message from our friend Farhan VU2ESE: 

I think the word 'annealing' is a bit of a misnomer. the idea is to thermally expand and contract the wiring a few times to relieve any mechanical stresses in the coil. after an extreme swing of tempuratures, the winding will be more settled.
this techniques owes itself to w7EL. I first read about it in his article on the 'Optimized transceiver' pulished in 1992 or so.
but all said and done, it is part of the lore. it needs a rigorous proof.
- farhan

https://groups.io/g/BITX20/topic/copper_wire_annealing/4101565?p=,,,20,0,0,0::recentpostdate/sticky,,,20,1,860,4101565,previd%3D1193595376000000000,nextid%3D1194269624000000000&previd=1193595376000000000&nextid=1194269624000000000

And here is another example of coil boiling: 

https://www.qsl.net/kd7rem/vfo.htm

-----------

I can almost hear it,  all the way from across the continent:  Pete N6QW should, please, stop chuckling.  Obviously these stabilization techniques are not necessary with his beloved Si5351.  Some will see all this as evidence of the barbarity and backwardness of LC VFOs.  But I see it as another example of lore, of art in the science of radio. (Even the FCC regs talk about "Advancing the radio art." ) This is sort of like the rules we follow for LC VFO stability:  keep the frequency low, use NP0 or silver mica caps, use air core inductors, keep lead length short, and pay attention to mechanical stability.  Sure, you don't have to do any of this with an Si5351.  Then again, you don't have to do any of this to achieve stability in an Iphone. But there is NO SOUL in an Iphone, nor in an Si5351.  Give me a Harley, a Colpitts, or a Pierce any day.  But as I try to remember, this is a hobby.  Some people like digital VFOs.  "To each, his own." 

Thanks Pavel. 

The Doug DeMaw Article that got me into Homebrew Double-Sideband

Just click on the images for a better view

Pete WB9FLW asked for this.  This was an important article for me -- it paved the way for my entry into homebrew phone gear -- this article was the basis for my first DSB transmitter, built in the Azores. 

I think Doug was a bit optimistic in saying that SSB operation was possible with this rig.  Maybe it was possible for Doug, but for most of us DSB is just a LOT easier to get going than SSB.  (I know that some people don't believe this, but I note that most of these folks have built neither DSB nor SSB rigs.  It always seems easier before you start to melt solder.)  

Be sure to check out the 10 meter DSB rig recently built by Mike WU2D.  He has 6 or 7 good videos on this project, including this one: https://www.youtube.com/watch?v=xThoAMv4zrw

Retro QRP Rigs of the 1960's, 70's, and 80's -- Video by Mike WU2D

It is time to put aside (again!) all of the heated ideological arguments about the power level that defines "low power."  Just sit back and enjoy this wonderful trip down QRP memory lane. 

Mike's description of the simple, single-transistor QRP transmitter was really nice.   I recently made something similar: https://soldersmoke.blogspot.com/2023/02/first-qso-with-high-school-receiver-100.html  And Mike does a nice plug for our beloved Michigan Mighty Mite.  Go CBLA! 

The modular idea:  words to live by my friends. 

40673!  TT2!  And G3RJV's PW Severn - indeed, bow your heads!

Wow, the Ten Tec Power Mite (or Might!) -- I still want one.  Same for the Argonaut -- what a great name (sounds like a "magic carpet), and with SSB to boot!  I want to join the Argonaut cult! 

I have both the HW-7 and HW-8 (the HW-8 is heading to the Dominican Republic).  This video makes me want to fire up the HW-7.  Maybe on 40.  

My 40 meter homebrew rig (Digi-Tia) has in it the filter from that old Yaesu FT-7 rig.  The filter was given to me by Steve "Snort Rosin" Smith.  https://soldersmoke.blogspot.com/2015/05/bitx-digi-tia-build-update-2-installing.html  

Thanks to Mike for including me in the credit roll at the end.  What a great group of people -- it is a real honor to be listed with those folks. 

The Franklin Oscillator: A Super-Stable VFO. Why No Attention? Why So Little Use?

My Franklin VFO

Lee KD4RE of the Vienna Wireless Society has been talking about the Franklin oscillator. He has been telling us that it is very stable, and capable of stable operation up through the ten meter band.  Lee wants to build an direct conversion receiver for all of the HF bands with one of these circuits. 

I was skeptical.  First, I'd never heard of this circuit.  I'd grown up in ham radio on a steady diet of Hartley and Colpitts and Pierce.  Vackar or Clapp were about as exotic as I got.  And second, I'd come to accept that it is just not possible to build a good, stable, simple,  analog VFO for frequencies above around 10 MHz.  For example,  in his Design Notebook, Doug DeMaw wrote, "VFOs that operate on fundamental frequencies above, say, 10 MHz are generally impractical for use in communications circuits that have receivers with narrow filters."  DeMaw was known for resorting to variable crystal oscillators. 

But then this month Mike Murphy WU2D put out two videos about his use of the Franklin oscillator circuit in a direct conversion receiver at 21 MHz.   The VFO was shockingly stable.  I began to believe Lee.   I fired up my soldering iron and built one.  

WU2D's Franklin Oscillator

Lee was right,  it is in fact remarkably stable, even at higher frequencies. My build (see picture above) was a bit slap-dash and could be improved a bit, but even in these circumstances here is what I got.   This was with a stable 6 Volt Supply and with only a cardboard box covering the circuit: 

Local time                  Frequency

0543                           19.1114 MHz  (cold start)

0636                           19.1116 

0804                           19.1117

1034                           19.1118

1144                           19.1117

I started digging around for references to the Franklin.  There was nothing about it in Solid State Design for the Radio Amateur, nor in Experimental Methods of RF Design.  Pat Hawker G3VA (SK) did discuss it in his Technical Topics column in RADCOM, February 1990.  Pat gave a great bio on Charles S. Franklin (born in 1879 and a colleague of Guillermo Marconi). But tellingly, Pat writes that, "Despite its many advantages, the Franklin oscillator remains virtually unknown to the bulk of American amateurs."  

QST "How's DX" August 1947

It wasn't always unknown.   In the 1940s, we see articles about the Franklin oscillator circuit. There is a good one in the January 1940 issue of "Radio."  The author W6CEM notes that the circuit "is probably familiar to only a few amateurs."  It shows up in the "How's DX" column (above). And the 1958/1959 issue of Don Stoner's New Sideband Handbook we see a lengthy description of the Franklin oscillator.  Stoner wrote: "The author's favorite oscillator is the 'old time' Franklin, and it is believed to be the most stable of them all! This rock-solid device can put a quartz crystal to shame! Because it represents the ultimate in stability, it is the ideal VFO for sideband applications."  And we see a PTO-tuned Franklin oscillator in the July 1964 QST. And it is in the fifth edition of the RSGB Handbook (1976). 

Here is the January 1940 "Radio" with the Franklin oscillator article on page 41 by W6CEM: 

https://worldradiohistory.com/Archive-Radio/40s/Radio-1940-01.pdf

Here is the July 1964 QST article: 

http://jlandrigan.com/files/PTO%20VFO/PDF%20PTO%20VFO%20Horn%20QST%20July%201964.pdf

There was an article about the Franklin oscillator in 73 magazine by W4LJC in February 1999: 

https://worldradiohistory.com/Archive-DX/73-magazine/73-magazine-1999/73-magazine-02-february-1999.pdf   

The author notes that: 

Much more recently (2022), Mike WN2A, modified his Mousefet transmitters (seen in QRP Classics in 1992) to include the use of the Franklin VFO circuit.  Mike's documentation is really excellent.  Kostas SV3ORA has a Franklin oscillator in his Super VFO circuit.  Hans G0UPL has one on his site. 

Look, there may be reasons why the Franklin oscillator has been ignored.  But the circuit sure seems to present a lot of advantages.  Stable operation beyond the 10 MHz barrier is the big one.  Simplicity is another.  If there are problems and shortcomings, let's hear about them. But it seems as if the Franklin oscillator may provide the opportunity for us to build stable VFOs beyond 10 MHz without resort to complicated PLL stabilization techniques, and without opting to go with an Si5351 or other complex digital devices.   

So let me ask:  Why hasn't the Franklin oscillator been given more attention, and why haven't we seen more use of this circuit by hams or even by manufacturers?  

Arnie Coro: Jaguey Rig Designed in 1982, More info on the Rig

Jaguey, Matanzas, Cuba

Dxers Unlimited's mid week edition for 23-24 October 2007

By Arnie Coro
Radio Amateur CO2KK

...

My own personal experience with the original JAGUEY direct conversion 

transceiver, designed way back in 1982, is that when used with a well 
designed front end input circuit, those receivers provide amazing 
sensitivity, with signals as low as 1 microvolt easily detected but, 
they do have one drawback, their selectivity or ability to separated 
between stations is very poor. The direct conversion radio receivers are 
used for picking up CW Morse Code Signals , Digital Modes and Single 
Side Band, but they are not good for receiving AM signals, and can't 

pick up FM modulated signals at all...

The original JAGUEY 82 Cuban designed single band amateur transceiver, was tested against a sophisticated and really expensive factory built 

transceiver. The tests showed that our design was at least as sensitive 
as the very expensive professional equipment, registering a measured 
sensitivity of less than one microvolt per meter, producing perfect CW 
Morse Code copy of such a signal. Adding well engineered audio filtering 
to a direct conversion receiver can turn it into a really wonderful 
radio by all standards amigos. 

Radio is a fun hobby, and believe me amigos, there is nothing more 
magical than listening to a radio receiver you have just finished 
building !!!

-----

Peter Parker VK3YE Found a nice description of the Jaguey by Cuban radio Amateur Jose Angel Amador from the BITX40 Facebook Group: 

A translation.  This was apparently in response to someone who thought they'd found a Jaguey schematic: 

"That's not an original Jaguey, that was a simple, single band, unswitched, 5 watt, DSB, kit for beginners with no gear and needing something to put on the license.

Carbon microphone direct to balanced modulator, two stages with 20 dB gain, W1FB/W1CER style feedback, and final with 2 x 2N2102 class B.
The receiver was more like that of the schematic, with a TAA263, easy to get from the FRC in 1978, and headphones. No need for an RF stage: the mixer was overloaded at night with European broadcasts above 7150.
The VFO is also inspired by Solid State Design for the Amateur Radio, a Colpitts with 2SC372 and a low gain feedback buffer with two 2SC372s.
Binocular ferrites were taken from Soviet TV baluns. The conditions of Cuba 1978.
Today I would make an SSB rig with polyphase networks, mixer with 4066,  and VFO Si5351.
The big complication of BitX is the crystal filter, they either get it made, or stick to a recipe, but few have what is needed to measure and tinker with crystal filters.

But why? Why Can't I Listen to DSB (or AM) on my Direct Conversion Receiver?

I've said this before:  I just seems so unfair.  We just should be able to listen to DSB signals with our beautifully simple homebrew Direct Conversion receivers. I mean, building a DSB transmitter is a natural follow-on to DC receiver construction.  And we are using AM shortwave broadcast stations (Radio Marti --I'm looking at you)  to test our DC receivers for AM breakthrough.  But when we tune these stations in, they sound, well, awful.  So unfair!  Why?   Unfortunately it has to do with laws.  Laws of physics and mathematics.  Blame Fourier, not me.  

Over the years there has been a lot of handwaving about this problem.  From Doug DeMaw, for example: 

In his "W1FB's Design Notebook," Doug wrote (p 171):  "It is important to be aware that two DSSC (DSB) transmitters and two DC receivers in a single communication channel are unsatisfactory.  Either one is suitable, however, when used with a station that is equipped for SSB transmissions or reception. The lack of compatibility between two DSSC (DSB) transmitters and two DC receivers results from the transmitter producing both USB and LSB energy while the DC receiver responds to or copies both sidebands at the same time."

That's correct, but for me, that explanation didn't really explain the situation.  I mean we listen to AM signals all the time.  They produce two sidebands, and our receivers respond to both sidebands, and the results are entirely satisfactory, right?  Why can't we do this with our Direct Conversion receivers?  I struggled with this question before: https://soldersmoke.blogspot.com/2015/07/peter-parker-reviews-dsb-kit-and.html  You can see in that post that I was not quite sure I had the answer completely correct. 

It took some discussion with a fellow Vienna Wireless Society member, and some Googling and Noodling for me to figure it out.  But I think I've got it: 

Imagine a station transmitting a DSB signal at 7100 kHz with a 1 kHz tone at the AF input.  There will be signals at 7101 kHz and at 7099 kHz.  Assume the carrier is completely suppressed. 

We come along with our DC RX and try to tune in the signal. 

Remember that they heart of the DC RX is a product detector, a mixer with the VFO (or PTO) running as close as we can get it to the suppressed carrier frequency (which we can't hear).  

Lets assume that we can somehow get our VFO or PTO exactly on 7100 kHz.  The incoming signals will mix with the VFO/PTO signal.  We are looking for audio, so we will focus on the difference results and ignore the sum results of the mixing.  

The difference between 7101 and 7000 is 1 kHz.  Great! And the difference between 7099 and 7000 is 1 kHz also.  Great again, right?  We are getting the desired 1 kHz signal out of our product detector, right?  So what's the problem?  

Here it is: SIDEBAND INVERSION.  Factoring in this part of the problem helps us see the cause of the distortion that plagues DSB-DC communication more clearly. 

Remember the Hallas Rule:   Whenever you subtract the modulated signal FROM the unmodulated signal, the sidebands invert.  So, in this case, we are subtracting that 7099 "lower sideband" signal FROM the 7100 VFO/PTO signal.  So it will invert.  It will become an upper sideband signal at 1 kHz.  We will have two identical 1 kHz signals at the output.  Perfect right?   Not so fast. Not so PERFECT really.  

The perfect outcome described above assumes that our VFO/PTO signal is EXACTLY on 7100 kHz.  And exactly in phase with the suppressed carrier of the transmitter.  But if it is even SLIGHTLY off, you will end up with two different output frequencies, signals that will move in and out of alignment, causing a wobbling kind of rapid fade-in, fade-out distortion.  You can HEAR this happening in this video by Peter Parker VK3YE, starting at 6:28:

And you can see it in this LTSpice simulation.  

This LTSpice model just shows two diode ring mixers.  The transmitter is on the top, the receiver is on the bottom. The transmitter has RF at 7100 kHz at L1 and audio at 1 kHz at R1.   The receiver has the VFO at 7100.001 L7,  DSB from the transmitter at L12 with audio appearing at R4.  It is instructive to watch the output as you move the VFO frequency.  If you move the VFO freq away from the transmit carrier osc frequency you will see the distortion.  Here is the netlist for the LTSpice simulation: 

http://soldersmoke.com/DSBDC.net

On paper, using simple mixer arithmetic, you can tell that it will be there. With the VFO/PTO just 1 Hz (that's ONE cycle per second) off, you will end up with outputs at 1.001 kHz and at .999 kHz.  Yuck.  That won't sound good. These two different frequencies will be moving in and out of alignment -- you will hear them kind of thumping against each other.    And that is with a mere deviation of 1 Hz in the VFO/PTO frequency!  We are scornful when the SDR guys claim to be able to detect us being "40 Hz off."  And before you start wondering if it would be possible to get EXACTLY on frequency and in phase, take a look at the frequency readout on my PTO.  

Now consider what would happen if the incoming signal were SSB, lets say just a tone at 7101 kHz.  We'd put our VFO at around 7100 kHz and we'd hear the signal just fine.  If we were off a bit we'd hear it a bit higher or lower in tone but there would be no second audio frequency coming in to cause distortion.  You can hear this in the VK3YE video:  When Peter switches to SINGLE Sideband receiver, the DSB signals sound fine. Because he is receiving only one of the sidebands. 

The same thing happens when we try to tune in an AM station using a Direct Conversion receiver:  Radio Marti sounds awful on my DC RX, but SSB stations sound great. 

My Drake 2-B allows another opportunity to explore the problem.  I can set the bandwidth at 3.6 kHz on the 2-B, and set the passband so that I will be getting BOTH the upper and the lower sidebands of an AM signal. With the Product Detector and the BFO on,  even with the carrier at zero beat  AM sounds terrible.  It sounds distorted.  But -- with the Product Detector and BFO still on --  if I set the 2-B's  passband to only allow ONE of the sidebands through,  I can zero beat the carrier by ear, and the audio sounds fine. 

There are solutions to this problem:  If you REALLY want to listen to DSB with a DC receiver, build yourself a synchronous detector that gets the your receivers VFO EXACTLY on frequency and in phase with the transmitter's oscillator.  But the synchronizing circuitry will be far more complex than the rest of the DC receiver. 

For AM, you could just use a different kind of detector.  That will be the subject of an upcoming blog post. 

Please let me know if you think I've gotten any of this wrong.  I'm not an expert -- I'm just a ham trying to understand the circuitry. 

Understanding a Very Simple Two-Diode Mixer

 

Take a look at the simple little mixer above.  I think I first saw it in SPRAT.  Thinking that it was really just a simplified version of the two diode Doug DeMaw mixer that I had been using for years, I couple of years ago I built it into a little Direct Conversion receiver.  It worked great.  But later, I began to have doubts about it.  In the words of young James Clerk Maxwell, I started to wonder about "the particular go of it." 

You see, the way the DeMaw mixer is set up,  both of the diodes are simultaneously on and off.  This has the effect of "chopping up" the incoming RF at a rate set by the VFO frequency.  Boom.  Fournier.  Mixing.  Great.  

But look at the mixer at the top of this post.  Here the VFO signal is coming in on the wiper of the 1k pot. The same signal is hitting both diodes at the same time.  The diodes are not being fed differentially.  So D1 and D2 are NOT both simultaneously tuning on and off.  Instead, when the wiper goes positive, D2 turns on while D1 is off.  On negative swings of the voltage at the wiper, D1 turns on while D2 is off.  For me, this made it a "mystery mixer." 

This reminded me of the sub-harmonic DC receiver I built earlier in the year:  The VFO runs at half the operating frequency, but the diodes are set up to switch on and sample the RF TWICE each VFO cycle.  This is the equivalent of having the VFO at the operating frequency.  

Could it be that this was just a sub-harmonic mixer with the VFO at the operating frequency? (I should note that Doug DeMaw published a design that actually made this mistake.  See:  https://soldersmoke.blogspot.com/2011/07/doug-demay-and-polyakov.html ) I knew that this would sort of work, but it would not work very well.  And the mystery mixer seemed to work very well.  Hmmm. 

I was loaning the DC receiver with the mystery mixer in it to a local high school.  I worried that I was loaning them something that I didn't really understand. I remembered that I'd been trying to figure out this mixer since early 2021:  https://soldersmoke.blogspot.com/2021/02/some-thoughts-on-singly-balanced-mixers.html  

Our beloved book, Solid State Design for the Radio Amateur (SSDRA) has an explanation of this circuit on page 74.  But this explanation didn't seen to work for me.  Check it out. YMMV. 

Bottom line:  I still couldn't figure this circuit out, so left it alone for while.  

The other day I woke up and looked at it with fresh eyes.  Suddenly it hit me.  Although the VFO was hitting the diodes in the same non-differential way as is done in the sub-harmonic mixer,  the RF (signal) is entering the mixer in a differential way.  This means that the two diodes are taking turns sampling the upper side of L2, then bottom side of L2, via L1 and L2.  This results in a complex repeating waveform that is similar to that of diode ring mixer.  Within that complex repeating waveform, there are sum and difference frequencies. I did some noodling on this: 

The key difference between this mixer and the sub-harmonic mixer is the way L2 is positioned:  In the sub-harmonic mixer, there is no differential feed of the RF.  Both diodes get the same polarity of RF.  The VFO switches on D1, then D2.  The RF is sampled at twice the VFO frequency.    But in the mystery mixer that had me scratching my head, the RF is fed to the diodes in differential form.  So while the diodes here are -- as in the sub-harmonic mixer -- being switched on and off sequentially, they are taking turns sampling the top and the bottom of L2.  That provides the complex repeating waveform that we need to get the sum and difference frequencies.  In a DC receiver the difference frequency is audio. 

What do you guys think?  Do I have this right?  How would you characterize this mixer:  Is it multiplying by 1 and 0?  Or is it multiplying by 1 and -1? 

This would be good mixer for a school project.  It is simpler than a mixer with a tri-filar toroid.