Monday, August 24, 2009

SW PSK-20 upgrade ideas

Lets face it, I cannot help it and have to think of alternative uses regularly.
QSOing on 20m in PSK31 is fun. However, I think there are more options for the PSK-20.

The first thing that came to my mind, adding some switchable local oscillators. The design of the PSK-20 is a 9.0MHz i.f. with a 5.07 l.o. (5.0688MHz crystal). Here comes the idea, one could add some voice channels using cheap crystals:
  • 14.120 = 9.0 + 5.120
  • 14.185 = 9.0 + 5.185
  • 14.200 = 9.0 + 5.200
Or, with oscillators divided by two:
  • 14.120 = 9.0 + (10.240 / 2)
  • 14.350 = 9.0 + (10.700 / 2)
Using (external) oscillators, one may consider using superVXOs for increased coverage.
This however would require to run a microphone preamp with an active low pass filter. The crystal filter of the PSK-20, for obvious reasons, is wider than a sideband filter.

The second idea is focused on the fact that the intermediate frequency is 9.0MHz.
As you may have seen, I was experimenting with a softrock lite on 30m. Those experiments where mainly aimed at the usablility of the softrock lite for 30m QRSS reception.
The softrock uses super-Nyquist, in short, the center frequency is 0.75 times the l.o.-frequency. This makes it comparably easy to use the softrock lite to "look" at a 9.0MHz i.f. with a l.o. crystal of 12.0MHz. This would add SDR and panoramic display to the PSK-20.
But, not only, since there also is a crystal 5.0MHz (or 10.0MHz divided by two):
  • 14.000 = 9.0 + 5.0
Reception of the better part of the CW band and the QRSS region at the lower band edge would be possible. For QRSS reception it would be advisble to pull the 12.0 MHz softrock l.o. down.

And finally, one could think of penning down a 5,0688MHz crystal, in order to reach the QRP frequency. All one would need for a CW qso would be a 800Hz sine generator.