[hpsdr] Odyessey-Siren Rev B.

[Robert McGwier]

Graham Haddock wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> All:
>
> 1.) In reading the schematics for the Siren Rev. B board, and comparisons
> to the Rev A design, I note that the ISD (QSD) is a 180 degree switch as
> compared to the 90 degree switch used in the Rev. A board.
>
> As I understand the operation of these switching detector/mixers,
> this will result in an extra 2 dB decrease in gain/NF or so in the
> conversion process.
>
> Is there a reason for doing this, or since it is intended to be used as
> a fixed IF, is it far enough back in the receiver that you don't care?
>
> 2.) How would I get to put my name on the list of people that could
> get one of the early Rev. B boards for test/evaluation purposes?
>
> Thanks,
> --- Graham / KE9H
>   

I don't believe this is correct.  I believe the two switches are 
operated in quadrature and they are inverted to achieve the opposite 
polarity.

The I line is turned on at both 0 and 180 and the input to the Op Amps 
is inverted by the switches at these points.   The Q line is turned on 
at 90 and 270 and the input to the Q line Op Amp is inverted by its 
switch.  Did I get this wrong? 

If I did get this wrong,  this reminds me of why my switches were so 
bloody complicated in the Horton diagram  because you lose SNR if their 
turn on times are not mutually exclusive.  The integrators are used 
instead of capacitors because analysis shows that Tayloe's view of these 
things are integrators yields superior theoretical performance without 
the need for ugly mitigation as done by other SDR's to achieve high 
performance.

73's
Bob
N4HY

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TAPR, Packrats, NJQRP, QRP ARCI, QCWA, FRC. ARRL SDR WG Chair
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