Podcasting since 2005! Listen to Latest SolderSmoke
Friday, January 31, 2025
Update from KK4DAS on the SolderSmoke Direct Conversion Challenge: BP Filter Added to Circuitry -- Full Video on BP Filter Soon
Radio Antenna Fundamentals Part 1 -- 1947 USAF Film
Thursday, January 30, 2025
Video of images and Data Stream: Huygens Probe Parachuting onto Titan
Diode Ring VFO Part II: How Much LO into a Diode Ring?
Tuesday, January 28, 2025
Other Workshops: Making The World's Smallest Motor
Monday, January 27, 2025
First 10 Meter AM Contact from Hi7/N2CQR
Sunday, January 26, 2025
Fireball (Meteor) Over the Dominican Republic
I hadn't seen one of these since March 1995 (I was in the Dominican Republic then too!):
7 MARCH 95 EVENING: POSTED ON CIS:
Also observed a pretty spectacular fireball in the North (near Polaris) at about 2330. So bright I thought it was a skyrocket. Very slow moving looking like pieces falling off it.
SolderSmoke Direct Conversion Challenge The Mixer and Diplexer
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
https://youtu.be/junuEwmQVQ8?
SolderSmoke Blog on Mixers:
https://soldersmoke.blogspot.
Join the discussion - SolderSmoke Discord Server:
Documentation on Hackaday:
https://hackaday.io/project/
SolderSmoke YouTube channel:
https://www.youtube.com/@
SolderSmoke blog DCR posts:
https://soldersmoke.blogspot.
Wednesday, January 22, 2025
A Tale of Woe from Mike WU2D, PLUS: The Importance of Band Noise
SolderSmoke Direct Conversion Receiver Challenge -- Soldering!
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.
No Bunching Up! It is Possible to Achieve Dial Linearity (and Stability) with an LC VFO
One of the major complaints about LC VFOs is that they allegedly cause "non-linear tuning." Essentially, this complaint claims that you will inevitably end up with your frequencies all "bunched up" at one end of the tuning range, with frequencies greatly "spread out" at the other end. BUT WE HAVE FOUND THAT THIS IS NOT NECESARILY TRUE. With a bit of careful design work, you can avoid the dreaded "bunching up." I have used the calculator in Bob's Electron Bunker to DESIGN VFOs that do not "bunch up" the frequencies.
Monday, January 20, 2025
SolderSmoke Direct Conversion Receiver Project -- Video #2 -- Building the PTO/VFO
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.
Links:
Join the discussion - SolderSmoke Discord Server
Documentation on Hackaday
https://hackaday.io/project/
SolderSmoke YouTube channel
https://www.youtube.com/@
SolderSmoke blog
SolderSmoke Direct Conversion Receiver Project: The Input to the Mixer from the VFO -- How Much Is Enough?
Saturday, January 18, 2025
Looking for Contacts on 10 meter AM from the Dominican Republic -- 29.005 MHz AM
I was listening to the Old Military Radio Net this morning and I heard Tim WA1HLR talking about some contacts that he had made on 10 meters, near 29 MHz. So I pulled my modified CB rig off the shelf, connected a power supply and my 10 meter vertical, and began to listen. Soon I heard CQs! One from G4ITR and then one from G4VZR. I now have high hopes for at least one QSO. So please, point those ten meter beams at the Dominican Republic and give me a call. I am on 29.005 Mhz.
73 Bill HI7/N2CQR
Wednesday, January 15, 2025
Ugly and Manhattan Construction from Popcorn Electronics
Some people apparently dislike these techniques. To each his own, but I like the Manhattan method. In fact, in the SolderSmoke Direct Conversion project, we are recommending the use of Manhattan circuit board tecniques. With Manhattan, you get a lot flexibility. At one point, for example, the High School students told us that they had forgotten to put a needed pad on the board. No problem! Just glue in a new one. Or if you put in one too many, just take one off.
You also keep all the circuitry and all the connections on one side of the board. This facilitates repair or modification. This kind of thing is not so easy when you have components on one side of the board and the connections on the other side. You spend a lot of time flipping boards over, breaking wires, trying to remember what goes where. Also, because the pads push the connections a couple of millimeters above the ground plane, I find that Manhattan technique actually reduces the chances for an accidental short to ground.
There has been some discussion of where the term "Manhattan style" comes from. Having been born on Manhattan island, I too wonder about the origin of the term. Some see it as the result of the grid pattern (like Manhatten's street grid) that results from the rectangular or square pads that are often used. Others point to the vertical parts placement that we see when looking at a board from the side -- the parts look like the skyline of Manhattan. Either explanation, I think, works.
Here is a Manhattan-style board I recently built in the Dominican Republic for my homebrew 15-10 meter SSB transceiver. I couldn't find any Gorilla glue here, so I went with Loctite Coqui. Same stuff. Latin American super glue!
The 10 meter Beacon at HI7/N2CQR (and reception reports)
Above is the 10 Meter beacon at HI7/N2CQR.
The first one to hear the beacon was Dean KK4DAS in Northern Virginia, within hours of it going on the air. Here is Dean's recording of what he saw and heard:thanks for info. 3 Watt can be loud on 10 if condx are good :)
The west direction skimmer setup on 10 m is a 6 el Yagi into a SDR with
AD9255 adc and XC7Z020 fpga.
A design by Pavel Demin which I am testing for a while now.
Enjoy the Caribean, here its minus 2 C and boot high snow.
73, Rico
DF2CK
Tuesday, January 14, 2025
Shock and Awe: The Story of Electricity --- Wonderful Video by Jim Al-Khalili (sent to us by Ashish N6ASD)
Jim talks about the early transatlantic cables, and why some of them didn't work.
We see Jagadish Chandra Bose developing early point-contact semiconductors (because the iron filings of coherers tended to rust in the humid climate of Calcutta!)
There is a video of Oliver Lodge making a speech. There is a flip card video of William Crookes (one of the inventors of the cathode ray tube and the originator of the Crooke's cross).
We see actual coherers.
There is simply too much in this video for me to adequately summarize here. Watch the series. Watch it in chunks if you must. But watch it. It is really great.
Thanks Ashish. And thanks to Jim Al-Khalili.
Monday, January 13, 2025
SolderSmoke Direct Conversion Challenge -- Video #1
This is the first in a series of videos and postings on the SolderSmoke Direct Conversion Receiver challenge. Dean, KK4DAS takes us through an overview of the project. He covers the architecture of the receiver, construction techniques, component sourcing and selection and generally sets the stage for the build. Future videos will cover each board in detail.
We are very excited invite you to join the SolderSmoke Discord server. This is an experiment to see if Discord is a good forum for SolderSmoke listeners to interact with us and each other on topics of interest. For now, we will be used Discord exclusively for discussion of the DCR challenge. To join the SolderSmoke Discord server click on the link below.
Links and references:
• Join the discussion - SolderSmoke Discord Server
• Documentation on Hackaday
• High Schoolers Build a Radio Receiver | Hackaday.io
• SolderSmoke YouTube channel
• SolderSmoke -- Homebrew Ham Radio - YouTube
• SolderSmoke blog
• https://soldersmoke.blogspot.
SolderSmoke Podcast #256: HNY SKN, LA Fires, Barkhausen! Southern Cross, Homebrew vs. Kits, AN762 Kit, Woe, Beacon, ARRL Kids, SDR Build, DC RX videos, Pete Hacked! Power alternatives, KWM4, Mailbag
Fires in LA.
Dean: Breaking the Barkhausen criteria.
Seeing the Southern Cross for the first time in 30 years.
For all three of us: The SolderSmoke Homebrew Challenge. And assembling a kit. https://soldersmoke.blogspot.com/2025/01/some-history-of-homebrew-ham-radio-from.html
https://soldersmoke.blogspot.com/2025/01/the-magic-that-only-comes-from-radio.html
https://soldersmoke.blogspot.com/2025/01/steve-g0fuw-talks-homebrew-and-kits.html
________________________________
Bill's (Southern) Bench:
-- SKN with QCX given to me by Bob. Thanks Bob!
-- Finishing up the AN762 .1kW amplifier. Socketry and relays. Working well.
-- A tale of woe: Some difficult troubleshooting on the 15-10 rig. Intermittent oscillation. Naturally I blamed the TJ DC RX AF amp. Spent a lot of time working on that amplifier. But problem always returned. Started looking at output from carrier osc/BFO. Waveform weird. Then weirdness disappeared and so did the whooping. So I rebuilt the entire carrier osc/BFO/ mixer board. Went back to singly balanced 2 diode mixer. Used LTSpice for the oscillator amp.. No more whooping. Turning the diodes on and off but not quite 7 dbm... Should I be concerned?
-- A 10 meter beacon! 28.233 Please listen. Send e-mail reports. Thanks to WN2A.
-- Antenna thoughts. Getting a tripod.
_______________________________
SHAMELESS COMMERCE! Mostly DIY RF! Lots of useful kits and boards there. I have used their TIA boards. Todd K7TFC is one of us. FB store.
Become a SolderSmoke patron. We need the help. Homebrew is under seige! We are one of the few sites, blogs, podcasts that are promoting it! Help us!
Buy stuff from Amazon and E-bay using the links on our sites.
------------------------------------------------
Dean's Bench:
-- ARRL kids day -- Exhausting.
-- VWS Makers SDR receiver build.
-- High School DC RX Build news. How to watch the videos.
_______________________________
Pete's Bench:
-- Hacked!
-- Power Alternatives.
-- Thermatron Finals
-- KWM-4.
__________________________
Mailbag
Dave Newkirk W9BRD (son of Rod). Great comments on homebrew radio. And a great picture.
Derek N9TD built the DC Receiver. FB Derek!
Peter VK2EMU at 39C in Australia. HOT!
Drew N7DA -- Some great comments on kits vs. homebrew.
Tommy SA2CLC has a nice video about fixing the cavity resonator in his HP8640. Respect!
Ben KC9DLM sent good presentation from India: https://github.com/kholia/talks/blob/master/Dhiru_My_RF_Homebrew_Adventures.pdf
Scott KQ4AOP and Derek N9TD offering to 3D Print PTO coil forms. FB!
Donnie WA9TGT on the beautiful signals from DC receivers.
Chuck KE5HPY's FB Altoids DC receiver.
Todd VE7BPO: POPCORN ELECTRONICS IS BACK! Thanks Todd. And thanks Vasily!
Jim KA4THC has his uBITX on the air and is making contacts!
Farhan VU2ESE fond memories of homebrew dinner with Wes and other HB Heroes (on the blog).
Charlie ZL2CTM -- About his new Pelican Case SSB rig.
Walter KA4KXX. All new hams should build a transmitter.
Buzz W3EMD A nice QSO on 10 and then a shout out to the Old Military Radio Net
Sunday, January 12, 2025
Some History of Homebrew Ham Radio -- From Wikipedia and from K0IYE
From Wikipedia: https://en.wikipedia.org/wiki/Amateur_radio_homebrew
In the early years of amateur radio, long before factory-built gear was easily available, hams built their own transmitting and receiving equipment, known as homebrewing.[2] In the 1930s, 40s, and 50s, hams handcrafted reasonable-quality vacuum tube-based transmitters and receivers which were often housed in their basements, and it was common for a well-built "homebrew rig" to cover all the high frequency bands (1.8 to 30 MHz). After WWII ended, surplus material (transmitters/receivers, etc.), was readily available, providing previously unavailable material at costs low enough for amateur experimental use.[3]
Homebrewing was often encouraged by amateur radio publications. In 1950, CQ Amateur Radio Magazine announced a ‘‘$1000 Cash Prize ‘Home Brew’ Contest’’ and called independently-built equipment ‘‘the type of gear which has helped to make amateur radio our greatest reservoir of technical proficiency.’’ The magazine tried to steer hams back into building by sponsoring such competitions and by publishing more construction plans, saying that homebrewing imparted a powerful technical mastery to hams. In 1958, a CQ editorial opined that if ham radio lost status as a technical activity, it might also lose the privilege of operating on the public airwaves, saying, ‘‘As our ranks of home constructors thin we also fall to a lower technical level as a group’’.[4]
In the 1950s and 60s, some hams turned to constructing their stations from kits sold by Heathkit, Eico, EF Johnson, Allied Radio's Knight-Kit, World Radio Laboratories and other suppliers.[5]
From "From Crystal Sets to Sideband" by Frank Harris K0IYE https://www.qsl.net/k0iye/
Dear Radio Amateur,
I began writing this book when I realized that my homebuilt station seemed to be almost unique on the air. For me, the education and fun of building radios is one of the best parts of ham radio. It appeared to me that homebrewing was rapidly disappearing, so I wrote articles about it for my local radio club newsletter. My ham friends liked the articles, but they rarely built anything. I realized that most modern hams lack the basic skills and knowledge to build radios usable on the air today. My articles were too brief to help them, but perhaps a detailed guide might help revive homebuilding. I have tried to write the book that I wish had been available when I was a novice operator back in 1957. I knew that rejuvenating homebuilding was probably unrealistic, but I enjoy writing. This project has been satisfying and extremely educational for me. I hope you'll find the book useful...
...My personal definition of “homebuilding” is that I build my own equipment starting from simple components that (I hope) I understand. I try not to buy equipment or subassemblies specifically designed for amateur radio. I am proud to be the bane of most of the advertisers in ham radio magazines. I still buy individual electrical components, of course. I just pretend that the electronics industry never got around to inventing radio communications.
An irony of our hobby is that, when the few remaining homebrewers retire from their day jobs, they often build and sell ham radio equipment. These industrious guys manufacture and sell every imaginable ham gizmo. I doubt any of them have noticed that, by making everything readily available, they have discouraged homebuilding.
Saturday, January 11, 2025
Friday, January 10, 2025
"The Magic That Only Comes from a Radio you Built Yourself" -- The Many Benefits of True Homebrew
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