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Monday, August 29, 2016

Update on the PA3GSV M4MMRX -- And a Mystery



Note the establishment of a new acronym (M4MMRX) for Lew McCoy's Mate for the Mighty Midget receiver.  We  have needed this acronym for a long time, and SolderSmoke HQ is proud to have come up with it.  We do our part my friends.

Jan has made more progress on his amazing Dutch M4MMRX and has produced a short video showing the receiver in action with SSB and CW signals. 

Here is a bit of intriguing homebrew mystery:  Jan has gone to a LOT of trouble to create that semi-circular opening in the center of the front panel.  He even cut a corresponding semi-circular hole in the sewer pipe cap that serves as the large wheel in his amazing homebrew reduction drive.  But he won't tell us what he plans to do with that space.  So I ask you, dear SolderSmoke readers:  What is that space for?  Why the see-through panel and sewer-pipe cap?  What is Jan's plan? 

From Jan:

Hi Bill,
 The rattle is gone, so I made a little video of the MMMRX in ssb and cw mode.

In the text, a ch327 and a ch45 crystal is mentioned, but I can’t get this to work.
The ch45 has a 453.6 kHz fundamental, for ch327 can’t find one.
The ch327 is a FT-243 one, tested several, but no fundamental somewhere around 455 kHz.
For ssb there is a ch45 and a ch46 crystal in, which should provide a bandwidth of about 2kHz.
(Still not totally in the clear how this should work with the very narrow resonance response of the crystals.
One should expect two peaks and nothing in the middle?)
For cw I found two ch45 crystals about 130 Hz difference in frequency, which seems to work well.

Still need to correct the 40m oscillator coil, then move on to finishing the receiver.
This is my first home brew tube superhet.
The project isn’t finished yet, but it sure is fun to build, and learned a lot during the process.

73  Jan

5 comments:

  1. I'll take a SWAG: Back-lit dial pointer? Philco used this on many '37-'38 models:

    http://radioattic.com/item.htm?radio=1070119

    ReplyDelete
  2. A singular element shape from the double helix of life, compressed and tuned to resonate with the radio gods, the angles so formed eliminate the sporadic oscillations within the enclosure, allowing said oscillations to escape in a mode encouraged via a transmission line tunnel, tuned by the thickness of the front panel - width, height and depth.

    ReplyDelete
  3. Swinging the BFO - simple! Parallel xtals in a VXO :) . If you want better, try a 455kHz Ceramic Resonator.

    ReplyDelete
    Replies
    1. Wider IF Filter? same thing. Wider for SSB, switchable to single xtal for Cw?

      Delete

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