[hpsdr] Odissey QSD circuit diagram

[Jim Miller]

I was looking at Phil's circuit and can't figure out something. IIRC, in 
order for the integrator summing junction to function the signals applied 
need to be within the loopgain of the integrator.

The signals applied to the integrator are the sum and difference freqs (and 
harmonics) of the received signal and the vfo.

I don't see how the sum frequencies are handled by the integrator since they 
exceed the available loop gain. Are they merely passed through to the 
passive filter that is behind the opa1632?

If so how then does this act to maintain the proper impedence mentioned 
below?

tnx
jim ab3cv


----- Original Message ----- 
From: "Bob McGwier" <n4hy at idaccr.org>
To: "Philip Covington" <p.covington at gmail.com>
Cc: "Giancarlo Moda" <i7swx at yahoo.com>; <hpsdr at hpsdr.org>
Sent: Friday, September 29, 2006 4:06 PM
Subject: Re: [hpsdr] Odissey QSD circuit diagram


***** High Performance Software Defined Radio Discussion List *****

Exactly.  As Phil discovered (see his blog) and as pointed out to us by
Tayloe,  we need an active integrator to provide the same impedance in
and out of band to get a good return loss for the filters in front of
the mixer.

Bob 


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