--- In [email protected], Cecilio Bayona <[EMAIL PROTECTED]> wrote:
>
> Ray Anderson wrote:
> > Dan-
> >
> >
> >
> > I missed the earlier part of this thread, but can you explain
what the
> > SA612 has to do with a QSD (quadrature sampling detector). The SA612
> > mixer is a double balanced Gilbert cell type circuit. No sampling is
> > involved.
> >
> >
> >
> > -Ray WB6TPU
> >
>
> >
> > ka9rza <[EMAIL PROTECTED] <mailto:wavelengths%40netzero.net> >
>
> You can integrate the outputs of any kind of mixer, and by using two
fed
> by a LO in Quadrature generate I/Q audio. The SA612A's have a
conversion
> gain so they make for a sensitive mixer.
>
> FET switches are not only highly efficient but have an extremely high
> IP3 compared to SA612A's
>
> Switches are far cheaper also, personally I'll stick with the switches
> unless going really high in frequency,
>
>
> Cecil
> KD5NWA
What you say is true in the case of direct conversion but what he's
doing is taking an IF signal from an existing receiver and splitting
it into quadrature ... since the output of an IF has a small dynamic
range because of the AGC the 602/612 are good for this (In fact they
are designed to use after the IF), especially for people who don't
want to fiddle with SMT IC's ... also since the oscillator frequency
will be fixed, getting your quadrature at oscillator will take a
fairly simply LC network instead of higher frequency oscillator and a
divider network
The downside is his IF filter will set his maximum bandwidth in
SDRadio or any othr SDR software he uses, so he doesn't get to see a
48Khz chunk of spectrum, only the 4-6Khz bandwidth of his IF filter
JR
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