Monday, January 4, 2010

Subharmonic SDR RX (TX?)

I still have not published any details about my subharmonic, yes, subharmonic, SDR receiver for 30m. Will come, I will tackle the diagram drawing later that day. So much is said, take a subharmonic local oscillator, split the signal in a I and a Q paths and delay (phase shift) the Q path by 45 degrees. Yes, it works, the 30m version really works, image canceling and everything.
30m is based on a 5.0688MHz canned oscillator.
Unfortunately, I could not find anything for 12m...

Here come the ideas for other bands:
Frequencies in MHz, the crystals for frequencies printed in italics are available at box73.de

80m
  • DATA/Voice - 1.800
  • Voice - 1.820, 1.856

40m
  • DATA/Voice - 3.535
  • Voice - 3.560, 3.579

20m
  • CW-range - 7.015
  • DATA - 7.030
  • Voice - 7.058, 7.122

17m (overtone CB crystals => divide by three)
  • best fit: 27.155, 27.165, 27.175, 27.185, 27.205

15m
  • Voice/SAT - 10.700

10m:
  • CW - 14.010
  • DATA - 14.055, 14.058, 14.060
  • Voice/SSTV - 14.200
  • Voice - 14.250, 14.252, 14.270, 14.285, 14.300, 14.318, 14.333
  • SAT - 14.7456

Some other options could be considered:

SW-BC
  • 75m - 2.000
  • 60m - 2.4576, 2.500
  • 49m - 3.000, 3.072
  • 31m - 4.9152
  • 25m - 6.000
  • 16m - 8.8672
  • 11m - 12.750

Weather FAX
  • DDH - 3.9321
  • GYA - 4.000
  • NMF - 2.97152

Weather TTY
  • DDK9 - 5.0688

SW-Navtex
  • 2.97152

It needs to be mentioned that the L.O. should put out a pure sine wave. The easiest way to achieve this is a crystal as a filter, as I did it in my 30m subharmonic direct conversion receiver. It seems tempting to use counters & co to reach more frequencies, but, the amount of filtering required would spoil the simple design...

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