Bill N0YUD built this really nice Michigan Mighty Mite. I like the wood base (with little feet!). And the classic black 35 mm film container. And the Vero board. Fancy connectors too! Nicely done Bill.
Bill has also wisely left space for a low pass filter. As you can see in his 'scope picture below, the MMM produces a lot of harmonics. With a low pass filter, that mess will turn into a beautiful sine wave. We'll be talking about harmonics and low pass filters in the next podcast.
Hi Bill and Pete,
I just completed my Michigan Mighty Mite and am proud to announce it seems to be generating about 1 watt of what appears to be extremely harmonically challenged RF. I was worried about the ugly signal on my scope until I saw another screen shot on the blog page that looked almost exactly the same as mine.
What a fun project and lots to learn with just 7, or in my case 8, parts (I had to stack a couple of 56ohm resistors). I utilized those small pc board sockets for the coil and crystal so I can easily change bands and also left room for a low pass filter....
I am still struggling with the tank coil theory and impedance... Impedance matching is a very murky area for me!
I am looking forward to building the low pass filter. By the way, I checked for third and fifth harmonics and could not hear anything on my receiver. There's another question, why does this circuit generate odd harmonics? Fun stuff, this learning game!
I love the Podcast! Thank you for your efforts and keep them coming.
'73
Bill McMillan
N0YUD
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
Hi Bill and Pete,
Some further adventures of the Michigan Mighty Mite - I have added several amenities since first oscillation:
Of all of these, I cannot sufficiently emphasize the importance of little rubber feet. A project just cannot be considered complete without them.
More pictures and details of the low pass filter are on my blog at http://n2htt.net
I've been heard on RBN on 40m several times, but haven't gotten any replies to calling CQ. This weekend was the December SKCC Sprintathon, and I pretty conclusively proved that if there are any other signals on the band the MMM is not likely to be heard.
I've had a lot of fun with this little rig, it's a keeper.
Keep up the great work with the podcasts, and Happy Holidays
73
Mike N2HTT
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Larry's rig looks like it is almost ready to go for Straight Key Night! FB. I was glad to heat that the crystal survived the rough treatment dished out by the US Postal Service these days. Apparently all envelopes are sent through a steam roller! Who knew?
Hi Bill and Pete,
As usual life has intervened in my plans, but after a delay for professional and personal reasons I can now report success in yet another additional the the CLA. I was able to successfully transmit into a dummy load yesterday with my new transmitter. It is not the prettiest device I have ever built but it is functional. I tried the home made mepad construction and it works fairly well. I did discover a few things while building and testing this unit. First, I need a new soldering iron with a little better temperature control. Second, before using this transmitter on the air (currently on a dummy load), it needs a low pass filter. I can see several harmonics imposed on the generated signal.
The first picture show how everything is mounted to piece of scrap wood for stability. I even screwed down the old key for stability during testing. The alligator clips are for the dummy load connection (the dummy load is also home built from 20, 1K ohm resistors which is located just on the right edge of the picture).
Even without an antenna I was able to receive the transmitted signal on my IC-7200 in the shack.
The signal on the scope is messy but the tome received on the IC-7200 sounds good.
Next steps are the additional of a Low Pass Filter and better matching to the dummy load (currently I'm only at about 49 Ohms).
Thanks again for the encouragement. I plan to do a little more tweaking on this unit and will keep you updated on any progress.
Have a great holiday and a Happy New Year,
73
Larry
AE7TM
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Steve W1KF's Connecticut Mighty Mite is the neatest build so far: it has a front panel and knobs and plugs and everything! Pete Juliano commented: "Very cool –and elegant. I loved the transistor in a front panel mounted socket with heat sink. Wished I had thought of that –great idea." Steve is on the air at grey line times, looking for contacts at 3.579 Mhz.
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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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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).
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We have been distributing quite a few 3.579 MHz crystals, but until today we hadn't seen a single new Michigan Mighty Mite. I commented on this in the last podcast. Pete came to the rescue and built one:
Hi Bill,
The MMM was built – took me a long time (about 30 Minutes so it was kind of slapped together). The most time was consumed drawing squares on the sheet metal. I used a pill bottle cut down for the coil.
Used a piece of Home Depot sheet metal for the based. I highly recommend a .01 Ufd from the 27 Ohm to ground –key clicks are awful.
BTW the circuit can be modified so that the tuning cap is soldered to one side of the coil and the other side to ground –essentially the tank tuning cap is in series with the 0.05 bypass cap and is effectively across the coil. Tribal Knowledge
The CLA lives on!
Pete
VIVA EL EJERCITO DE LA LIBERACION DEL COLORBURST! VIVA EL CLA!
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A thing of beauty! Check out the key!
What a great diagram. Schematic included!
Remnants of mine
Steve "Snort Rosin" Smith's
More on all this:
Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htmOur coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmokeOur Book Store: http://astore.amazon.com/contracross-20
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