Hi Ron,
I used the term "by definition" for a reason. Popular legend to the
contrary, the Orion is not an SDR. (Neither are the IC-756Pro II or
IC-746Pro, for that matter - except for their DSP engine.) It is a
software-controlled radio. No software known to man or beast will alter one
whit of the IF frequency, local oscillator range and RF bandpass-filter
parameters which determine its frequency coverage. These are all
"hard-wired" in RF hardware. The same remark applies to the PA low-pass
filter bank.
By definition, the Orion's TX/main RX 9 MHz first IF (as opposed to a first
IF above the highest operating frequency) will in and of itself preclude
continuous transmit and receive coverage, which are prerequisites in HF
equipment intended for the mil/gov radio services. There is a "forbidden
band" around the 9 MHz IF which cannot be incorporated into the radio's
coverage whilst maintaining acceptable image and spurious suppression. Even
if the more RF bandpass filters and PA LPF's are added to provide contiguous
passbands, this limitation imposed by the low first IF will still apply.
The only solution is to place the first IF above the highest
transmit/receive frequency, e.g. at 64 or 70 MHz, and down-convert (RX) and
up-convert (TX) to the final (DSP) IF. This will call for a complete
redesign of the radio's RF/IF chains.
I hope this adequately addresses your question.
Cheers for now, 73,
Adam VA7OJ/AB4OJ
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