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Thursday, December 17, 2015

Modulated Michigan Mighty Mite?


This suggestion from across the pond is a bit "out there."  In fact, for me it brought to mind the famous line from the Noel Coward song about who goes out in the mid-day sun...  This does seem like an endeavor for our stoic British cousins.  You'll need a very stiff upper lip to AM modulate a Michigan Mighty Mite!  Peter's observation about the "SSB kilowatt nerds" resonated with me and reminded me of the reaction I got when I tried to put a DSB rig on the air in London.   But hey, go for it Peter!   Please let us know the results.   For those who are rock-bound in the CW portion of the band (like 3579) this might be something fun to try using a dummy load -- just to see if you can send an AM  Mighty Mite signal across the shack.

Hi Bill,

Your recent Soldersmoke thoughts re. MMMites have been niggling my imagination; I think radio should be fun, educational, simple and cheap, to encourage young folks to get a license and "appliance users" to melt some solder.

Mike Rainey (AA1TJ) and Jim Kearman (KR1S) have done superb work in reducing RF circuits to a functional minimum... so egged on by a certain Mr. Bill Meara, I'm looking at modulating a MMMite Tx on 80m and building the simple Rx to go with it. I chose 3615kHz as it's a frequency UK VMARS (Vintage Military Amat Rad Soc) use for A.M. - the SSB kilowatt nerds who think the sky will fall down if A.M. corrupts the ionosphere have accepted a few enthusiasts firing a watt or ten of A.M. skywards. I
blame you want to say thanks for setting my mind in this direction.

See how this sounds: modulate a MMM by inserting an electret mic capsule (2 terminal type) between the transistor base and ground,  not forgetting the RF choke from the electret capsule output to the base bias 10k resistor, to avoid the xtal feedback signal being absorbed in the electret...

Yep, that's it: job done, the MMM now produces A.M. as the base current, fed by 10k from the +ve rail in the original MMM, is now partially shunted to ground by the electret capsule. I'll adjust the base bias resistor to get 50% "no speech" carrier and good mod. depth. I'm trying to avoid a mic amp stage; keeps it simple & sweet. If I can get 500mW in total, that's ~ 100mW in each sideband - on a good day with a following wind, on 80m that should go a mile or twenty.

Which leaves a drop dead simple Rx to design - somebody has done similar,
HERE, You got it: an LM386 audio amp as a regen Rx. I had considered the ZN414 TRF Rx, or it's modern equivalents, but they are nowhere near as common as an LM386, or as cheap. IF it works on 80m...! Or, I could try an xtal controlled regen Rx, as per Mike / Jim's designs. Either which way, I'm sure I can find a cheap, simple and effective Rx - but if you know of any.....?

Cheers Bill, TTFN!

Peter Thornton G6NGR

2 comments:

  1. Valuable information ..I am delighted to read this article..thank you for giving us this useful information.
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    ReplyDelete
  2. Bill,

    Do you see a pattern here? The name Peter must have some magic mojo connected to the other end of the soldering iron. I will leave you with Peter Parker and Peter Thornton who are always pushing the bubble along the radio path.

    ReplyDelete

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