--- Mark Erbaugh <mark@microenh.com> wrote:
> Thanks for the reply. I went back and reviewed your
> original posting.
Note that posting was before I had used the Time Machine
board. Even so the results were almost the same whether I
used the SDR-1000 as the IF or the Time Machine board. So I
have very little doubt that the results would still be
essentially the same using a Softrock board.
> I hadn't really looked at the Pegasus mixing scheme, which
> kind of messes up
> what I was thinking about. I was really thinking about
> using some frequency
> in the Pegasus (I forgot about the 45 MHz) as the VFO for
> the QSD. That
> would require a frequency near the intended tuning range,
> which probably
> doesn't exist in the Pegasus.
You might be able to make use of a divide by 4 of the Pegasus
1st LO (it tunes ~40-75 MHz in 2.5 kHz steps). If you intend
to use the BPF stages of the Peg this might not work so good
since the desired Pegasus LO frequency divided by 4 will
likely have already switch in a wrong BPF/LPF filter for the
band you are trying to work. So given the various design
constraints of the Peg I would most likely stick to working
with the existing 455 kHZ IF for any external DSP IF
experiments.
> I have modified both my Pegasus and my RX320 to bring out
> the 12 kHz IF and
> have decoded that with a computer, but I was thinking that
> a QSD mixer might
> work better, plus you would be able to get twice the
> bandwidth if you have
> both I and Q - though I hadn't thought about the roofing
> filter.
I've concluded that when trying to modify any existing radio
for external DSP IF you will always be confined to the
bandwidth of the IF circuits. So bandwidths to work with for
DSP IF experiemtns will always be limited to 20 kHz or less.
Can be usefull for sure but may as well write off any hope of
having a wideband panadpater display.
Duane
N9DG
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