[Premium-Rx] SDR as a means of decoding low-frequency IF output of premium receivers

[Rothenburger Conseil]

    Charles Steinmetz wrote:
>     Do you intend to design your own sampled IF using an A/D or DSP eval 
>     board (or your own board design), or were you looking for a 
>     plug-and-play solution that someone has already developed?
    Let me first thank you for your interest and question.
    But before repying let me thank as well openly here ( as I did privatley already)  Rick Wisney with his reply ( use of SDR-14),
    Jack Smith ( Spectrum Lab option ) and Brooke Clarke ( SDR-IQ solution).

    Well, I was think of both solutions and anything in between. As I wrote, I'm rather familiar with  developped or commercial solutions. I infact, I use a PMSDR on my MAC but currently under Windows XP/BootCamp with H2PHD, Alberto' SW. Fine.But only usable frequencies ( hence IF)  above some 150kHZ. Its Si570 LO does'nt allow for work below.
    So, yes , I was contemplating solutions such DSP eval boards with ADC on board.
    BUT: I run accross an old article from F5MI about sub-harmonic sampling and Spectrum Lab SW hinted by Jack Smith.
    I think we DO NOT  need full bandwidth ( from 0 or near zero to 30 or 33kHz)! We need merely a bandwidth of 3 or say 6kHz ( for AM - no interest for FM as myself is concerned),e.g.  a bandwidth  translated to 0 Hz - 6kHz here. So feeding directly an audiocard on PC running SpectralLab SW might work with relevant combination of choices of operations and/or additional scripts and  provided the entry anti-aliasing filter of the audiocard  permits it . It should given their corner frquency where attenuation starts is about 24kHz. Their sampling rate being 48kHz, a down-conversion to 18kHz would occur in the system with a bandwith of those 6kHz .With  digital filtering and digitaln BFO of 18kHz, a SW detector should then decode that digital signal down to digital audio prior to conversion.
    Although this discussion being perhaps more suited for relevant SDR -Groups, any further comments herer on this would be appreciated.

    Thank you again.

    Pierre, F3WT.