Building a Better Diode Ring Balanced Modulator (with Knack Karma)

So yesterday Pete and I were talking about Dave W2DAB's Michigan Mighty Mite malady. Dave is tantalizingly close to the joy of oscillation.  Wizard that he is, I think Pete diagnosed the problem with his eyes closed from 3000 miles away.  I sent Dr. Juliano's prescription to Dave this morning and expect the concrete canyons of Upper Manhattan to be ringing with pure 800 Hz tones as soon as Dave fires up his soldering iron. 

Anyway, I then told Pete that I'd been looking through my bookshelf for something suitable for my 11 year-old nephew Sebastian.  I found something for him, but I also came across a book that was too advanced for the young fellow:   "The Master Handbook of Ham Radio Circuits." TAB Books, 1977.  By "The Editors of 73 Magazine."   Between turkey sandwiches I started looking through this book.  I immmediately found an article of interest:  "A Better Balanced Modulator."   The author (unnamed) looks closely at the performance of our beloved and much-used diode ring mixer with dual trifilar transformers.  He concludes that the unbalanced input and output coils (in the traditional configuration) detracts from the balance needed for optimum carrier suppression.  He suggest the use of baluns at input and output (see above) and claims significant improvement in carrier suppression.   Very interesting. (If anyone wants to dig into this, e-mail me.)  There is also a very simple solid-state VFO circuit that promises phenomenal stability.   

Anyway,  I found myself trying to remember where this great book came from.  Then I remembered someone sending it to me.  A quick check of my e-mail revealed the source:  Dave W2DAB sent it to me three years ago.  Thanks again Dave!  


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35% Off on Bill's Books

35 % off on "SolderSmoke" (the book!),  "Contra Cross", and my new book: "Us and Them" 

All available in print and e-book form here: http://www.lulu.com/spotlight/soldersmoke

Sale through Dec 3.


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Graham G4UEK has THE KNACK

Thanks to Stephen for alerting me to the homebrew page of Graham G4UEK:

http://www.sandrock.org.uk/radiostuff/Rigs.htm

I really liked the description of his progress as a homebrewer, and the way he was helped by G-QRP, SPRAT and Ian G3ROO.  FB.

Graham has a nice personal ham radio story:

http://www.sandrock.org.uk/radiostuff/Radio.htm

Thanks Stephen!  Thanks Graham!   

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Ben's Mighty Mite -- IT IS ALIVE!

Ben KD9JNQ is the first of the Colorburst Liberation Army (CLA) recruits to get his Michigan Mighty Mite to oscillate.  So he has been promoted to Colonel. 

Ben writes: 

Bill and Pete, thanks again for the encouragement!

EL CLA UNIDO JAMAS SERA VENCIDO

Ben
KD9JNQ


Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Colorburst Explained

http://en.wikipedia.org/wiki/Colorburst

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Bill's Dominican Mighty Mite (1993)

If you look closely, just in front of my keyboard you can see the Michigan Mighty Mite that I rebuilt this morning (scroll down to see the previous post).  Looks like I was using a polivaricon as the capacitor.  Other than the cap, all the parts used in this 2014 version were from the 1993 effort.  Here is how it is described in "SolderSmoke -- Global Adventures in Wirless Electronics": 

    I decided to start off slow, with small projects that seemed likely to succeed.  The secretary in our office in the Embassy, Mady Bullen, had an interest in ham radio that had been sparked by service in far-off places where short-wave was the only way to talk to home.  She would pass me old issues of CQ magazine.  It was in the March 1992 issue that I found the Michigan Mighty Mite.

    It was originated by Ed Knoll, W3FQJ and developed by Tom Jurgens, KY8I. It is about as simple as you can get in a radio transmitter: just one stage, a crystal controlled oscillator.

    An oscillator is basically an amplifier in which some of the output signal is fed back into the input.  If you provide enough feedback in the right way, the amplifier will “take off” and begin generating a signal.  The howl you hear when the microphone of public address system gets too close to the speaker is this kind of signal.  The speaker (the output) is sending energy back to the input (the microphone) and what was an amplifier turns (annoyingly) into an oscillator.  In this case it is an audio frequency oscillator because all the filters and tuned circuits in the PA system are built for the audible frequencies.  But the same thing will happen at radio frequencies.  That’s what the Michigan Mighty Mite is all about. 

    I put the thing together using parts obtained from the Santo Domingo Radio Shack store. The resonant circuit used a coil that was just some wire wound around a discarded plastic 35mm film container.  Homebrew radio projects rarely work the first time you power them up.  I had to fidget with this thing quite a bit—obviously there wasn’t enough feedback.  I had my Drake 2-B on and tuned to the crystal’s frequency.  As I poked around on the little circuit board, I suddenly heard a little chirp from the 2-B.  There it was!  The little device that I had put together was producing radio frequency energy on the 40 meter band.  Hooray!  The joy of oscillation!  Now I felt like I was truly in league with Faraday and Marconi, with Shep, Stan and Bollis, and with Serge! Hilmar would have been proud of me (but he still would have been horrified by my sloppy wiring). 

    I never was able to talk to anyone with that little device—the power output was very low, and my antenna for the 40 meter band was very poor.  But it didn’t really matter.  I had had my first real success at homebrewing a piece of ham radio gear.

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Bill's Re-Born 1993 ColorBurst Michigan Mighty Mite

So far we've sent out 9 of these color burst 3.579 MHz crystals.   It occurred to me that I should make sure these particular rocks work with the Michigan Mighty Mite design we've been advocating.  So today -- still in something of a turkey-induced haze --  I pulled out the surviving remnants of the MMM that I built back in 1993.  That one had been for 40, so I rewound the coil for 80 using the data from this MMM site: http://www.qsl.net/wb5ude/kc6wdk/transmitter.html   

I was hoping that this rig might oscillate even without the variable capacitor, but mine did not.  Once the cap was placed in the circuit, the oscillations began.  It sounds pretty good on my Drake 2B. 

I have not yet wound the secondary (antenna) coil but (as I suspected) the oscillator works fine without it. 

So, no excuses folks.  These cheap junk box crystals work.  Time to build one of these things and join the ranks of hams who have homebrewed a transmitter (and, of course, The ColorBurst Liberation Army).   

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20