Just to separate this subject from the very long SDR thread...
If you want to use (for example) FlexRadio's free PowerSDR software in conjunction with one of your existing receivers... you do not need to build a SoftRock (or equivalent) mixer board.
I.e., you can obtain all of the features and functions of a SoftRock + PowerSDR combination by building the simpler mixer circuit shown in the .jpg attachment, and also described here:
http://mysite.verizon.net/sdp2/id12.htmlThis circuit consists of a crystal oscillator, a 1/N frequency divider, and a mixer. There is no need to produce two local oscillator signals that are 90 degrees out of phase, there is no need to employ two mixers (to produce I and Q outputs), and there is no need for any transformers and/or inductors to form a bandpass filter at the input.
Select the crystal oscillator frequency so that the frequency of the output of the frequency divider is 11 kHz
lower than the frequency of the i.f. output signal you plan to obtain from your receiver.
Plug the output of the mixer into your sound card (left or right side, but
not both).
You're all set to go!
Note: the reason you don't need I and Q (in phase and quadrature) outputs is because the i.f. output of your receiver does not contain any significant signals in the "image band" of frequencies that are on the
lower side of the local oscillator frequency of your mixer board (i.e., frequencies between 33 kHz and 11kHz
below your receiver's i.f. frequency). Even if you pick the "16KHz" bandwidth setting on an R-390A, the i.f. filter rolls of at 8kHz on either side of 455kHz. The only purpose served by using both I and Q outputs of a SoftRock (or equivalent) mixer is to employ the "phasing method" (rather than a filter) to remove image band frequencies.
Stu
