I've thought about variations of this idea and even done some
basic RX experiments with it. My most serious experiments to
date using this basic idea were over a year ago using a
Corsair II as the tuning and BPF. I simply tied into the CII
immediately after the 9 MHz first IF. My very simple and low
effort to implement experiments were actually very
encouraging. See my initial posting and the follow up
comments to this group from Dec 04 regarding this:
http://lists.contesting.com/archives//html/TenTec/2004-12/msg00116.html
I haven't really done much else with CII/ESS-TM board combo
since last spring as I've shifted onto other projects. I do
think about working on it some more from time to time because
the CII would be easy to modify for both DSP IF RX and TX
with an ESS-TM board. The TX level out of the TM board is low
enough to feed back through the 9 MHz 2.4 kHz wide IF filter.
>From there the native CII 1st LO mixing scheme and PA chain
would take care of the remaining transmitter parts of such a
modified radio. Things like PTT and ALC would also be pretty
easy to implement in a Corsair as well. And the best part is
that the CII would not be modified beyond restoration. In
fact I'm sure it can be done in such a way that CII can be
100% restored to factory original.
In the case of the Pegasus and its design similar siblings I
often thought that the 45 MHz IF is the best place to apply
this idea. Unfortunately in the case of the QSD that high of
a frequency is a bit of a challenge to get to. Although I
think decent results could also be had by applying the QSD to
the 455 kHz IF of the Pegasus instead. The other limitation
of using a radio like the Pegasus or its sibs for such work
is that the 45 MHz IF roofing filter will limit any
QSD/external DSP IF to ~15 kHz of bandwidth. To me that is
too restrictive given the increasingly common use of 96 kHz
bandwidth in the SDR radio programs like Rocky, PowerSDR, and
Winrad. I suppose if you only want a narrow bandwidth IF then
that is not an issue (that's exactly what I had with the CII
experiments I did). I suppose with some creative design you
could actually do both bandwidths, narrow for optimal DR
performance and wide for panadapter purposes.
Also in the case of the Pegasus and its sibs the prospect of
TX with a QSE (or any other baseband to RF mixer scheme) may
be a bit challenging to implement, not likely to be a
"restorable" mod to make. For some reason I can't ever bring
myself to making mods of this level to a radio that can't be
undone.
And finally I do know that there are some that are taking the
12 kHz IF out of the RX 320(D) and feeding it directly into
Winrad. This works because Winrad does not need I/Q inputs to
work. This was discussed within this last week on the RX 320
group on Yahoo.
Duane
N9DG
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