A Possibly Blasphemous Redraw of the Michigan Mighty Mite Schematic

Ryan KJ7KVD is building a Michigan Mighty Mite.  I sent him some parts, and mentioned that I had redrawn the schematic.  I find that it sometimes helps me understand a circuit if I just re-draw the schematic.  

Above you will see what I came up with.   Here is what I told Ryan: 

Attached is my re-daw of the MMM schematic.   The emitter and base resistors just needed some clarification.  The original schematic led some to believe that the two resistors should be connected.  Not so!  I think the redraw clarifies this.  

The most significant re-draw is in the coil.  All I have really done is to "pull out" the tapped "tickler" coil.  You will read in the literature that the two are equivalent.  This just shows that L1 can be seen as a separate coil, imparting RF to the parallel LC tank circuit that is tuned to the operating frequency.  The phase shifts introduced by the transistor, the tank, and the crystal all add up to the needed value in order to meet the Barkhausen criteria:  Oscillation results! 

Go ahead and build the coil with the tap as in the original schematic.  This re-draw may help you understand how the thing works.  Understanding is important.  

Here is one of the orignial schematics (from https://www.qsl.net/wb5ude/kc6wdk/transmitter.html): 

SolderSmoke 264: CW TX, Repair of 17-12 Rig, AI and Repair, Back on 40m, HB for 2m, VWS WSPR Makers Project , MAILBAG

QSO May 8, 2026 with Lou EA3JE.  I was using my Mythbuster

May 12, 2026

SolderSmoke Podcast #264 is available for download: 

Audio:   http://soldersmoke.com/soldersmoke264.mp3

Video:  https://www.youtube.com/watch?v=_9FcfuqjZxA

We had a small recording glitch at the beginning of this video. But we didn't lose much. We had talked about the success of the SolderSmoke Direct Conversion Receiver Project. We talked about the receivers built by Nader Omer ST2NH and Chuck Adams AA7FO. We had also gloated a bit about our April 1 post -- you know, the (bogus! ) story about how the Administration is "Supporting Homebrew Radio." (Let us know if you were taken in by this, even for just a few seconds.) At that point, we were just beginning Pete's section; that is where the recording began. Here are the notes for the rest of the podcast:

Pete: 

Three CW transmitter projects featuring low parts counts.  Good results from Reverse Beacon Network. 

The goal in these projects is to raid the junk box and severely limit any new purchases of components.  Pete had no idea of the depth of parts he bought and just stashed away.   https://www.youtube.com/watch?v=5YLZ7aZpmxQ&t=30s

Bill: 

Fixing the 17-12 Rig.  Parasitic VHF Oscillations with the SK3050.  Good advice from Gemini. Killing NE602s. Fat Finger Syndrome -- hard to work with ICs.   Different freq when on transmit -- need for .1 uF cap on pin 8. Worked South Korea -- TRGHS. 

Putting the DIGI-TIA back on the air. On 40! And SW listening with the Q-31. 

Hard to homebrew for 2 meters.  Did some beacon experiments to Puerto Rico on last day in DR. 

SHAMELESS COMMERCE DIVISION: 

The importance of Patreon!  Thanks!  patreon.com/SolderSmoke

Mostly DIY RF!  https://mostlydiyrf.com/

Universe Today Podcast with Fraser Cain.  No Ads.  Great stuff.  Listen!   https://www.patreon.com/public-rss/75186?show=1744036

Dean: 

The VWS WSPR project.  

Mailbag:  

Ed N3EML  Heard me on 40 with my Digi-Tia

Grayson KJ7UM  Liked WWII training video: https://soldersmoke.blogspot.com/2026/05/radio-receivers-1942-training-film.html

Mike WN2A  -- Pete Juliano is our Shifu! (Lexicographer Steve Silverman KB3SII approves,)

Todd K7TFC Thoughtful comments on ARRL "Clean Signal Initiative."

Danny ON1MWS's regen with unusual variable capacitors. 

Mike WU2D  S-38, Nearfest,  Mu Metal.  https://www.youtube.com/watch?v=YUQ4xml1dSY

Charlie NJ7V  Interviews Mitch NK3H who homebrewed an SSB transceiver. 

Charlie also had Don KM4UDX, President of the Vienna Wireless Society on the podcast. 

Bob KD4EBM -- El Cilindro. Radioactive Hospital Waste -- basis for a Ruben Blades song.  It was 1987 in Brasil.  Cesium 137 left in hospital waste.  

Hamilton  KD0FNR   Big fans of "The most interesting man in the world."https://soldersmoke.blogspot.com/2026/04/background-from-maine-on-most.html

Rhett KB4HG -- TW-100! Used on the OMRN. https://soldersmoke.blogspot.com/2026/05/the-tw-100-fly-away-transceiver-cw-ssb.html

What happened to Glenn KU4NO's homebrew rig? https://soldersmoke.blogspot.com/2018/07/a-rig-with-maximum-soul-5-band.html

Ryan KJ7KVD is listening to OLD SolderSmoke podcasts.  He will build a Michigan Mighty Mite. 

Will N5OLA restored a Heath SB rig.  We now know why they went to HW rigs.   https://www.youtube.com/watch?v=Bt2d1Ia8lqQ 

Paul G0OER -- Thanks us for PTOing the HB world, but sends us a video of a unique Eddystone receiver with 39 permeability tuned coils!  https://www.youtube.com/shorts/L4oQHU5_kQk?feature=share

Rick N3FJZ -- A very cool video today on his homebrew HF power amplifiers:  https://www.youtube.com/watch?v=-CUVAF4HyfY

Farhan VU2ESE -- I heard from him yesterday as he was landing in Chicago. 

Mitch NK3H Talks Homebrewing with Charlie NJ7V of Red Summit RF

This is a really cool interview.  Both Mitch NK3H and Charlie NJ7V are members of the SolderSmoke Direct Conversion Receiver Hall of Fame.  Mitch has built a dual-band superhet rig, which is the subject of this interview: 

https://www.youtube.com/watch?v=wK_EVt5iAQ4

Here is a video Mitch did about his SolderSmoke DC receiver:  

https://soldersmoke.blogspot.com/2025/05/mitch-nk3hs-fb-soldersmoke-direct.html

Mitch also built the Michigan Mighty Mite.  And he did an SSB version! 

Mitch is a very interesting guy.  He was a professor,  he worked in biotech, founded his own company which was funded by venture capital, later retired, got interested in astronomy,  and came to ham radio at the start of the pandemic.  Wow, great stuff. 

In Charlie's video, Mitch provides a lot of good explanation of his experimentation process.  I had to chuckle when Mitch pointed out that he did NOT invent the Colpitts oscillator.  Good point Mitch!

Mitch credits Pete N6QW as one of the people who helped him design his superhet transceiver.  He also mentions Farhan VU2ESE, Alan Wolke W2AEW and several others.  FB.  And he credits SSDRA, EMRFD and ChatGPT.   Mitch also likes the videos of the IMSAI Guy.  

Mitch has already made 50 contacts with this rig. 

Mitch makes excellent use of microcontrollers and digital VFOs.  He provides great info on the speed and cost of various sources of commecial PC boards. 

Quote of the day from Mitch:  "Electrons don't care how pretty or ugly your board is!"

Mitch concludes with a quote from Pete N6QW: "You gotta know stuff to do stuff." But Mitch adds to this an important coda:  "But the process of doing it is the learning experience."  Exactly right Mitch.   
 

Thanks to Mitch and Charlie for a really great video:  https://www.youtube.com/watch?v=wK_EVt5iAQ4

U.S. Administration Supports Ham Radio Homebrew

 

In a decision that puzzled many analysts, the Federal Communications Commission has come out with a new policy that seems to support the at-home construction ("homebrew") of amateur radio equipment.  The commission outlined a series of new requirements (see below) that, collectively, seem intended to breathe new life into what many considered a dying art.  

Commission spokesman Brian Cox tied the move to recent efforts by the Administration to bring industry back to the United States:  "For too long we have stood by and watched foreign manufacturers take larger and larger portions of the electronics market in the United States.  Part of this seems to be the unwillingness of many Americans to do what their grandfathers did and actually build their own electronic equipment. These steps are intended to help reverse that trend." Greene's comments may have been undercut by the fact that they were sent from his FCC-provided Iphone (which allegedly was not homebrewed in the USA) and then disseminated via Tik-Tok.  

Sources in the Administration also point to recent tariff moves by the government that will have the effect of removing the incentive of cheap foreign-made equipment.  "Just wait until those 1000 percent tariffs kick in.  You can almost feel those soldering irons warming up!" 

Collectively, this initiative seems tied to the political effort known as MAGA.  An anonymous White House spokesman explained: "First there was MAGA (calling for a return to GREATNESS).  Then came MAHA (HEALTH!).  Now we see MASA:  MAKE AMERICA SOLDER AGAIN.  We think this will be a real winner.  There will be so much winning, American hams will soon get tired of winning."  

The emphasis, a spokesman explained, will be on DOMESTIC production of radio equipment.  "We see the Michigan Mighty Mite as a good example.  I mean it just oozes domesticity!  MICHIGAN!  Why can't we go back to the day when millions of MMM rigs dotted our fruited plains, and people happily conversed via Morse Code using homemade transmitters?  Well we can.  And dammit we will, whether people like it or not!" 

Construction techniques will also be closely regulated, and the naming of these techniques has become an issue:  "We like the 'Manhattan' style of construction, but the name is too, well, too 'New York City.'  So we are re-naming the technique:  From now on it will be known as the 'Mississippi Technique.'  We also discovered that all of the Crazy Glue used in the Manhattan -- I mean Mississippi -- Technique comes from overseas.  So from now on, only good-old Elmer's Glue can be used.  MASA!" 

In a related move, the FCC announced that henceforth, only American Morse will be permitted in the United States. The use of International Morse Code will be banned, and masked ICE agents will destroy any equipment found to be using it.  "I mean, we invented it right?   So when did we go all 'woke globalist international'?  Enough of that."  It is hoped that this move will reduce the number of radio contacts with foreigners, something the FCC finds "highly woke suspicious."  "Americans should  be talking only to other Americans, right? "  An exception seems to have been made for one country: contacts with Russia will be allowed to continue.  No explanation for this exception was provided. 

SolderSmoke Direct Conversion Receiver-- N7HPR Handout #1 -- The VFO

 

I like the way Steve N7HPR did this:  First, that he had a working receiver on display to serve as a prototype.  Second, that he asked the students to come up with their own Manhattan board designs and third, he provided templates that would allow them to properly place their Me Pads. 

We did some of these things with the high school students.  We definitely had a prototype on display, and they looked at it a lot.  We did ask them to deisgn their own Manhattan boards -- as I recall, the response to this was uneven at best.   The templates are a good idea that we did not try with our group build.  

One big advantage of building the VFO first -- the students get something of the Michigan Mighty Mite sensation.  They have successfully built a source of RF, a transmitter!  We had one of the students move around the room with his oscillator (battery powered) turning it on and off as he listened to the tones from a DX-390 receiver.  This is very similar to the demonstration that Marconi did with the very first radios.  

More tomorrow.   

Thanks again Steve.

Why 3.579 MHz for Old Color TVs? The Origins of the CBLA

As the Commanding General of the Color-Burst Liberation Army, I have often wondered why so many of these 3.579 MHz crystals were made.  Heck, even the crystal filter of my first homebrew superhet receiver used these crystals.   

When we launched the CBLA effort, we used the Michigan Mighty Mite as our transmitter of choice:  I mailed out around 40 of these rocks.  Many transmitters were built.  I have received reports of guys pulling their cars over to the side of a road (with hapless family members in the car) when a discarded color TV was spotted -- the 3.579 Mhz crystal would be quickly extracted.  Such was the dedication of the CBLA members (the family members were, of course, baffled).  

Anyway, the story of the Color-Burst crystals is deeply entwined with the story of the birth of color TV.  This fellow (above) does a good job of explaining the hows and whys of 3.579 MHz. Thanks to Al Williams and Hackaday for alerting us to this, and for some really useful commentary on the video: https://hackaday.com/2025/12/18/the-miracle-of-color-tv/

Viva el CBLA! VIVA! 

WD4CFN Makes Contact Using the SolderSmoke Direct Conversion Receiver and a Michigan Mighty Mite

 

Hall of Fame member Steve WD4CFN in Tennessee fired up his 40 meter Mchigan Mighty Mite (above) and made contact with ND4K in Georgia. FB Steve.  Congratulations OM! 

SolderSmoke Podcast #260 FDIM, Hollow State Design, Pete's Bench and the Shelf of Shame, Direct Conversion Project News, How Best to Preserve this Blog?, Dean's Bench and the Desk of Despair, Bill's Bench and the Garage of Grief, MAILBAG

SolderSmoke Podcast #260 is available: 

Audio version:  http://soldersmoke.com/soldersmoke260.mp3

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

Quote from the Old Miltary Radio Net:  "Being on the leading edge is great, but sometimes being on the trailing edge is more fun."  Indeed. 

Heard from an Australian on the Southern Cross Net:  "My antenna needs a lot of Viagra!" 

News from Dayton/Xenia/FDIM: Dayton Xenia.   Again, we didn't go.  But Bob Crane W8SX was there and got a nice interview with Grayson,  Hans, and Farhan.  We are presenting these and more.  Michigan Mighty Mite Revival at FDIM!  Jeff W9TH. 

Farhan's review of Hollow State Design: I am compelled to set aside the future of my family and to orphan my cats to resume work on the 250v power supply that I built last year. Inshallah, Allah favors those who favor thermatrons!   Grayson's book is  imbued with deep experimental insights and littered with gems. You have to read it over and over to find new things each time.   It goes into my reference shelf in the lab."  Buy it here: https://www.ermag.com/product-category/books/ 

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

PETE'S BENCH:

Pete working on JF3HZB dial.  Send Pete a Heath mono-bander! 

MHST on shelf of shame? Even the great ones have to take a break every so often. On the importance of taking a break. Ernest Rutherford 1917 and all that:  https://soldersmoke.blogspot.com/2025/05/on-importance-of-taking-break.html 

Channelized 40 meter rig. Heard in Arizona by Andy KB7ZUT on a HOMEBREW SSB Reciever.  Very rare.   SWL HB2HB. 

Pete:  Thumb broken as a Novice?  Early episode of Fat Finger Syndrome? 

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

DC RX NEWS:  

Quote from N6QW:  "The radios do not build themselves!"  

Alan W2AEW finishes Direct Conversion Receiver. And even he worries about feedback! 

Phil W1PJE MIT receiver  (with cool MIT stuff).  Coming to see us! 

KN6FVK's Barkausen-Be-Gone Spray :https://soldersmoke.blogspot.com/2025/05/john-kn6fvks-fb-homebrew-soldersmoke.html

Indian hams working DC RX. VU2JXN Ramakrishnan, VU2TUM  Puneit Singh, Ashish N5ASD, building one in Bangalore with 3D printed form from Scott, KQ4AOP.  Ramakrishnan is planning on building a second receiver with his daughter. On June 22, 2008 in SolderSmoke #86 we reported on the birth of Ramakrishnan's daughter.  This is that same daughter! See: https://soldersmoke.blogspot.com/2024/01/long-time-soldersmoke-supporter.html    How to get a PTO form in India.  A tip from Ramakrishnan: "I got the 3d printing done via https://robu.in with 1:1 size. After uploading the stl, I received it by post in 5 days or so."

German students of Andreas DL1AJG.  and Canadian students of Daniel VE5DLD. 

Receiver built in Singapore!  9V1/KM7ABZ

John M0XJA reports 8 members of his club are building this receiver. 

Chuck N4AVC got his PTO coil form 3D printed at the local library. For free!  FB! 

Few admit to being fooled by April Fool story.  But still, inspirational. VK3HN was going for a few seconds -- SOTA AI chatbots? John West liked the 85th harmonic threat. 

What next after DC RX?  Choose carefully! Don't bite off more than you can chew. 

Do some mods!  Build something else!  And remember to be a homebrew Elmer.  Help someone else build the receiver. 

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

SHAMELESS COMMERCE DIVISION: 

Check out the SolderSmoke blog on the WayBack Machine.  The blog, not the podcast.  www.soldersmoke.blogspot.com   Would this be a useful backup if Google were to pull the plug on blogspot?  Is the format OK?   Is the template recoverable?  How best should  we backup the SolderSmoke blog?  

Be a Patreon SolderSmoke Sponsor!   Please subscribe to the YouTube channel!  Buy your Amazon stuff through our link.  Buy stuff from Mostly DIY RF.  

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

DEAN'S BENCH:

Dean has completed his Mythbuster: https://kk4das.blogspot.com/2025/05/kk4das-mb-20-transceiver-complete.html   Plexiglass top! 

Diode switching. 

Dean:  Build of the SDR receiver.  Microscope required? 

____________________

BILL'S BENCH:

VK6JDW and HCJB in the Kimberly. 

The stages of separation:  Shack, Garage, Car trunk:  HP-8640B and HAMEG scope saved from garage. HP-8640B repair.  HAMEG Modulation Monitor. 

=================

MAILBAG

-- Wouter ZS1KE.  Thinks Soviet spies COULD homebrew.  Hamilton KD0FNR concurs. Agent Sonya and Soviet Spy homebrew. Copacetic Flow. I dunno....I dunno... 

-- Hamilton KD0FNR grew up in New Mexico, supports my idea of Starlink deorbit. See : https://www.kallmorris.com/columns/goodness-gracious-green-balls-of-fire

-- Adam N0ZIB Heard my 10 meter beacon from the DR.  28,233.5 MHz  On now. 

-- Rick N3FJZ  Great memory Direct Conversion messages. 

-- John KN6FVK had fun with DC RX. Tattoos on Board. We need a high sign! Like the Little Rascals. 

-- Adrian M7EFO DC RX builder in GQRP.  FB.

-- Steve KW4H Kits not the same as homebrew, but old Boatanchor kits have value. 

-- Mike WU2D -- Old buddy Charles Kitchen SK. 

-- Craig -- Some really nice feedback on Hack-A-Day re DC RX and Dean's videos. 

-- Peter VK3TPM proposes a certificate for SolderSmoke DC RX Honor Roll. 

-- Michael WN2A used a 3 inch reflector from Northern New Jersey. Edmunds Scientific "Space Conqueror"  

-- Phil W1PJE and Mike WN2A lament that our eyes don't pick up radio frequencies.  This would be a great troubleshooting tool! I can SEE the IMD!  Perhaps some tin foil hats? 

-- John WPE9IRS SW listener! Heard my beacon.  Many SWLs switching to tuning in ham stations. 

-- Peter VK3YE found a homebrew 160 meter double-sideband transciever at a hamfest.  He also found "Solid State Basics for the Radio Amateur -- A QST Anthology"  NOT SSDRA.  But good!

-- Peter VK2EMU  From the Southern Cross (I took a picture of it in the DR!)  Building the DC RX!

 

Ramakrishnan VU2JXN

Mitch NK3H's FB SolderSmoke Direct Conversion Receiver -- "Incredibly satisfying!"

Wow, Mitch NK3H has built a really nice receiver. (He says it is not pretty, but those of us who have built one or who are in the process know that it looks great.) The SSB really sounds good also. 

Mitch writes: 

It's not pretty but it works! Incredibly satisfying. In answer to the questions, (1) though I 'd built a few small Manhattan style boards (e.g., Michigan Mighty Mite) this was more complicated. I've been using W1REX's island cutter to create isolated areas on the copper clad board, rather than pasting on pieces of circuit board. But the islands are a little small for as many as four connections on one island, as in most of the transistor bases. Inevitably a component lead would inadvertently contact the ground plane and all bets were off. Tracking down the shorts was challenging. (2) Once I got to the audio amplifier board I carefully laid out all of the components before starting to solder. But as I finished each stage and was ready for the next, I always seemed to be missing a resistor or two. I'd search the desk and the floor -- very frustrating. Turns out the speaker magnet was collecting and hiding the missing resistors. Lesson learned. (3) Next I'm hoping to build a transceiver. Still looking for the right project, probably a little more digital than this wonderful DCR.

Mitch obviously learned a lot during this project.  I had similar experiences with pads on the same level as the surrounding board -- I found that the 1 or 2 mm of elevation provided by the Manhattan pads prevented a lot of inadvertent shorts to ground.  And I too "lost" (temporarily) a lot of components to the magnet in the speaker.  

Good luck with the next projects Mitch.  With the Michigan Mighty Mite and the DCR under your belt you are ready to go.  Maybe a Double Sideband transmitter to go with the DCR? Or, as you said, perhaps something more digital.  There is a lot of good ham experience with the Si5351 digital VFOs.  Or maybe even an SDR rig.  

Thanks Mitch.  Congratulations and welcome to the Hall of Fame. 

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

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

Grayson Evans KJ7UM Interview at Four Days in May at the Dayton Hamvention 2025

 

LISTEN TO THE INTERVIEW HERE: 

http://soldersmoke.com/KJ7UM at Dayton 2025.mp3

Grayson said quite a lot in this short 4 minute interview: 

-- At FDIM he was selling his wonderful book "Hollow State Design for the Radio Amateur."  Buy one here: https://www.ermag.com/product-category/books/ 

-- Grayson was also selling a Thermatron version of our beloved Michigan Mighty Mite transmitter.  It is crystal controlled for the 40 meter band, but the Color Burst Liberation Army approves! Here is a wonderful video on this rig:

https://soldersmoke.blogspot.com/2024/09/excellent-new-video-from-grayson-kj7um.html

And be sure to watch Grayson's excellent course on Thermatron Homebrewing: 

https://soldersmoke.blogspot.com/2024/02/grayson-evans-kj7um-video-on.html

-- Asked why someone should build with tubes when so much good solid state stuff is available, Grayson makes some especially excellent points:  The solid state gear is often filled with mysterious little black boxes -- we often don't really know what goes on in there.  Thermatron construction provides a break from complicated SDR nonsense "that is not really radio."  That last comment will generate some criticism, but not from here.  I think Grayson is right,  He earlier expressed admiration for complex circuitry, but he also rightly defends simple, understandable rigs.  

Here are Grayson's Technical Documents (a real treasure trove):  https://kj7um.wordpress.com/

Three cheers for Grayson.  And thanks to Bob Crane W8SX for doing this interview.  

Daniel VE5DLD's FOUR FB Saskatchewan SolderSmoke Direct Conversion Receivers

Daniel VE5DLD is a teacher in Regina, Saskatchewan, Canada.  Back in early 2023 several lucky students joined him in building the SolderSmoke Direct Conversion receiver.  We had asked people to build the receiver -- we wanted to test the design before asking the local high school students to build it.  Daniel and his students came through for us, and ended up having far more success than we did.  Congratulations Daniel!  Welcome to the Hall of Fame. 

Daniel wrote: 

Hi Bill!  Yes, I had my own DC Receiver that I use every so often for fun and 3 built by my students.  All working.  We didn't get any video because we just finished the school year and the kids left, but I've kept in contact with them and they told me they have been able to receive signals from their homes.  The kids developed excellent troubleshooting skills gained large amounts of confidence in their ability to fix things.  Over the next year, my students told about fixing their gaming consoles and fixing problems in their parent's electronics.  They are certainly no longer afraid of opening something up to see what is going on!  And that's what makes me the most happy!  Yeah, you can just recognize myself and only mention that 3 students were able to build DC receivers.

And yes, the Michigan Mighty Mite was a fantastic gateway to home brewing!

Thanks for thinking of me and my students!

73

Daniel D.

VE5DLD

On June 19, 2023,  Daniel wrote: 

We got everything going and all 3 students now have receivers capable of inhaling RF.  We 3D printed some knobs and hot glued them.  We took one outside but didn't hear any signals.  Mid afternoon is not good for 40m.  We will try again later this week and I'll bring my KX3 to make sure there is a single for them to listen.  This issue on that last radio was an improperly installed J310.  The angle is was installed hid the problem well!  Here are a few pictures of the completed rigs. 

Back in 2015, Daniel built a Michigan Mighty Mite.  I was pleased to be reminded that I had sent him the crystal.  Go CBLA!  For more info on Daniel's transmitter see: 

https://soldersmoke.blogspot.com/2015/10/saskatchewan-mighty-mite-video.html

Thanks Daniel! 73  

___________________________

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

Brian KA0PHJ's CBLA SolderSmoke Direct Conversion Receiver

Brian KA0PHJ finished his receiver in early March, and has been adding mods ever since.  He hopes to build another one for 80 meters and to use it with his Michigan Mighty Mite.  

VIVA EL CBLA!  VIVA! 

Brian writes: 

Bill,

I got my DCR finished in early march (built as designed), then added the RF gain, fine tune and frequency display. 

Wow, what fun!!

Gave me an excuse to organize all my discrete components and finally buy a Rigol!  

Now I plan to build one for 80m to go with the CBLA Michigan Mighty Might:) 

Keep up with good work. 

73,

Brian.

KA0PHJ

FB Brian!  Congratulations! 

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

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke

Erik N2EPE's SolderSmoke Direct Conversion Receiver

Erik built a really nice receiver.  I was glad that he took to heart our advice on the need for a large, insulating tuning dial.  He made one!  As he made this entire receiver. 

Eric wrote:  

I would like to make a homebrew QSO! I am learning CW, mainly because I find it easy to use QRP/POTA. I have a Michigan Mighty Mite, but it has not reached farther than my backyard yet, so a CW transmitter in the single Watt range would be a great next project. 

Congratulations Erik! 

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

For more information on how you too can build the receiver: 

Join the discussion - SolderSmoke Discord Server:

https://discord.gg/Fu6B7yGxx2

 

Documentation on Hackaday:

https://hackaday.io/project/190327-high-schoolers-build-a-radio-receiver

 

SolderSmoke YouTube channel:

https://www.youtube.com/@soldersmoke 

Sam WN5C uses ChatGPT as an Emergency Elmer

Sam WN5C has been on the blog before.  Last year we covered his heroic use of a Michigan Mighty Mite at Thunderbird State Park:  https://soldersmoke.blogspot.com/2023/06/sam-wn5c-builds-michigan-mighty-mite.html

This time, Sam writes about a good  ham radio use for ChatGPT: 

Hope you’re doing well. Just a quick note: ChatGPT is turning out to be a great homebrewing tool for me.

My elmer has been swamped with family issues, so my basic questions (“can you explain this circuit for me”) and hard questions (“why doesn’t this circuit I built work?!”) that he usually responds to right away has been a bit delayed. I’m in the process of designing a 5-band QRP CW transceiver with a superhet receiver and SSB receive so I’m learning a bunch of new circuits.

 

I’ve hated the idea of AI as someone who writes a lot (it cheapens what I’ve spent my career trying to perfect!), but man it is smart. I can ask it all kinds of questions. For example, it helped me design a little IF amp last night and ensured I got my impedance matching right (it’s great for mashing up lots of circuits and ensuring they work together). I can ask it for suggestions on part types and values. It helps with Arduino code if you’re into that. You can use plain language but it does well with heavy jargon. And, which I find really cool, it will step you through troubleshooting. It teaches the math, too.

 

Anyway, you or your readers might find this helpful. Especially when one is building at 3 AM and needs an answer immediately.

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

Thanks Sam! 

 

Excellent New Video from Grayson KJ7UM on his Thermatron version of the Michigan Mighty Mite

Here is a really wonderful video from Grayson Evans, KJ7UM, author of Hollow-State Design for the Radio Amateur.  

I really loved this video.  Throughout we see Grayson's sense of humor.  Early on he explains the differences between a tube (what remains from a roll of paper towell), a valve (like the plumbers use) and a THERMATRON (like a 6146).  Grayson is the inventor of the word Thermatron.  We should all pledge to use it whenever possible. 

Grayson's humor also shows up when describing the parts acquistion process for the Thermatron Michigan Mighty Mite.  He puls out a coil (a huge coil) and laments that it is not -- despite its large size -- sufficiently inductive. 

There are wonderful shout outs to SolderSmoke, to Electric Radio, to the Color Burst Liberation Army, to Pete Juliano,  and to Rex Harper.  

Grayson describes the utility of Rex Harper's Thermatron ME pads.  

During the video, Grayson actually builds the Thermatron MMM.  In under 2 minutes!  He then experiences the Joy Of Oscillation, or JOO as it has come to be known.  OM needs a contact -- listen for him on 3579.  He is calling CQ.  

Grayson talks about his book, Hollow-State Design.  I have a copy with me here at SolderSmoke Shack South in the Dominican Republic.  Great stuff.   The above link takes you to Lulu, where you can order the book.  You can also get it from Electric Radio Magazine here: https://www.ermag.com/product-category/books/

Thank you Grayson for bringing us this video, and so much more over the years.  And for giving us the very useful and fun word:  THERMATRON!  

Ciprian YO6DXE Puts the Michigan Mighty Mite on AM! (video)

Excellent work Ciprian!  

Here we have a Michigan Mighty Mite being modified for AM in Romania, with input from Hungary, and inspiration from Melbourne, Australia (Peter Parker VK3YE).  With a very nice shout-out to SolderSmoke.  

I really like Ciprian's emphasis on having fun with the electronics. 

TRGHS! 

SolderSmoke Podcast #248 -- Back from the Summer -- Spurs and Filters, S-meters, 6BA6 mania, Shirtpocket rigs, MAILBAG

The PsssT Kit, coming soon from Mostly DIY RF

SolderSmoke Podcast #248 is available for download: 

Audio: http://soldersmoke.com/soldersmoke248.mp3

Video: (800) SolderSmoke Podcast #238 -- Spurs and Filters, S-meters, 6BA6 mania, Shirt-pocket rigs, Mailbag - YouTube

Travelogue:  Trip to the Dominican Republic 3-9 August.  Thinking about the M0NTV video on mixers...  

Solder Smoke Shack South is almost done.   I am thinking about workbenches, operating tables and antennas.  How high should an electronics workbench be?   Table height?  Or workbench (woodwork) height?  

My son and I went to see "Oppenheimer"  Trinity test scene very cool.  They wanted to see if the gadget would work! 

Is the SolderSmoke blog completely archived on the WayBack Machine?  Please check and let me know.  Thanks. 

Bill's Bench: 

-- I've been working a lot of DX with the homebrew rigs:  Indonesia, Australia, Japan, Hawaii.  Lots of fun.  15 meters has been especially good. But the rigs still need work: 

-- M0NTV's video got me to put TinySA to work.  I found that output from dual banders could be improved.  Spurs and harmonics. Yuck.  I need more TinySA -- ordered the TinySA Ultra. 

-- Allison KB1GMX helped a lot.  EB63A amp was unstable, especially on 10 meters.  Higher frequencies are harder!  Tightened up shielding, negative feedback, and bypassing.  This all helped, but I found that I needed to take the higher frequency LP filters out of the amplifier box.  W3NQN filters are better, with steeper skirts and better 2nd harmonic rejections. NanoVNA proving very useful. https://www.gqrp.com/Datasheet_W3NQN.pdf

-- Also worked on the Bandpass filters for these rigs.  Farhan's comments on skirts of different filter configurations.  Some are "LSB" filters (with steeper skirt at the highest freq) and some are "USB" filters (with the steeper skirt at the lower frequency)  See diagrams on the blog page. So I built USB new filters for 12 meters and for 10 meters. 

-- Danger that my unshielded wooden box rigs might be inviting feedback.  So I shielded the 1510 rig with copper guitar amp tape (conductive adhesive).  Good stuff.  

-- Phase Noise rears its ugly head again.  See blog posts. 

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

SHAMELESS COMMERCE DIVISION:  

Mostly DIY RF getting ready to release PsssT kits.  Target date:  December 18, 2023 (E Howard Armstrong's birthday).  https://mostlydiyrf.com/

Amazon Search box seems to have died.  I can't get it back.  Can anyone tell me what happened?  (There seems to be "explanations" from Amazon about this, but they are written in a strange language that I cannot follow.)  Something similar happened with the Google Ads on this blog page.  Apparently you can't have ads both on YouTube and blogger.  

But hey, there is Patreon for those who want to support the podcast and blog. 

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

Pete's Bench

An S-meter for Bill? 

6BA6 Mania! 

QRP SSB with 6BA6

Shirtpocket rig re-build

Mailbag: 

Walter KA4KXX has a great article about homebrewing in the September 2023 QCWA Journal.  

 Steve KC1QAY -- Has joined the CBLA.  I sent him a 3579 crystal.  He built a MMM and experienced JOO.  And Allison KB1GMX is in his local radio club.  TRGHS. 

Ajay VU2TGG in Pune, India -- launching a high school receiver effort. 

Denny VU2DGR The Wizard of Kerala: https://soldersmoke.blogspot.com/2023/08/the-wizard-of-kerala-india-denny-vu2dgr.html

Joe VK4BYER working with kids a remote Australian community.  FB. 

Todd K7ZF -- Wants to get into homebrewing. Advised him to start small. 

Dean KK4DAS:  Fixing Hallicrafters Worldwide RX. Ciudad Trujillo!  Got question from Mark in the VWS Makers Group:  HOW DOES Michigan Mighty Mite REALLY Work.  See blog. 

Trevor Woods -- Info on Super Islander Mark IV made in Cuba from old CFL bulbs.  FB. 

Bob KD4EBM sent me some great stuff:  Sony SW receiver,  QCX Mini.  Made a CW contact with the QCX.  Felt virtuous -- it is going to the DR.  Thanks Bob. 

Peter KD2OMV:    One of the guys I worked with the ET-2 transceiver.  Great to hear from him. 

Armand WA1UQO   Richmond area radio museum? https://www.youtube.com/watch?v=BSCmljje1p8

Mike WN2A -- Sent me a great care package with lots of toroids.  A lifetime supply!  Thanks Mike!

Nate KA1MUQ got his Doug DeMaw receiver going after 38 years!  FB.  Been there, done that! 

Tony: G4WIF Liked Valveman video about Gerald Wells.  He visited him! https://soldersmoke.blogspot.com/2023/08/valveman-story-of-gerald-wells.html 

Dean KL7MA  Bill talked to him on 15 SSB.  He had worked Wes W7ZOI!  FB! 

But How Does the Michigan Mighty Mite REALLY Work?

Dean KK4DAS and I were talking to Mark, a new homebrewer.  After we sang the praises of the Michigan Mighty Mite,  Mark asked us a good question:  How does it really work? 

I guess the starting point for analysis is the Barkhausen criteria (that Pete N6QW taught us):  essentially you need enough feedback to overcome losses in the circuit, and this feedback has to be in phase with the signal at the input.  The MMM is clearly oscillating, so the question becomes, "How does this very simple circuit meet the Barkhausen criteria?" 

Here goes: 

Even though it is a very simple circuit, it is worthwhile to separate out the things that it has to do: 

1) It needs to set the AMOUNT of feedback.    This is done by the tap on L1.  Too low down on the coil, and it is too close to ground through the .05 uF capacitor (not enough feedback).  Too high on the coil and you get too much feedback.  This is like an inductive voltage divider. 

2)  It needs to make sure that this feedback is in phase with the input signal. Positive feedback. Q1 is an inverting amplifier.  So it supplies 180 degrees of phase shift. As the signal at the base goes more positive, the signal at the collector goes more negative, and vice versa.  But we need an additional 180 degree shift to bring the output signal in phase with the input signal.  Here is the key:   The crystal provides the other 180 degrees of phase shift.  See

https://www.allaboutcircuits.com/technical-articles/understanding-the-operation-of-quartz-crystal-oscillators/

I tested this:  A 3.579 MHz crystal does provide the needed phase shift:  It introduces a shift of about 190 degrees.  Check out this very cool picture. The two scope probes are looking at the input and the output of the 3.579 MHz crystal with 3.580 MHz frequency coming from my HP sig gen. 

Click on the picture for a better view.

3) It needs to filter out other signals -- the 365 pf variable cap resonates with L1 at around 3.579 MHz.  This results in maximum circulating current through L1 at this frequency. 

4) It needs to match impedance to the antenna.  L2 wound over L1 forms the secondary of a transformer and efficiently moves the energy from the MMM to the antenna.  Think about the gears on your bike. 

The 10k resistor biases the base of the transistor, keeping it on.   The 27  ohm resistors limits the current through the transistor, preventing it from burning up. Note:  the 27 and 10k resistors should NOT be connected directly to each other.  There is no dot in the schematic. This causes some confusion among builders. 

The .05 uF capacitor does two things:   It grounds the L1/365pf tank circuit for RF (but not for DC).   It is less than 1 ohm at 3.579 MHz.   And it helps reduce (smooth out) key clicks (very sudden on-off changes in the oscillation).