[hpsdr] Odyessey-Siren Rev B.

[Robert McGwier]

Graham Haddock wrote:
>
> >>Graham Haddock wrote:
> >> 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.
>
>
> > Robert McGwier wrote:
> > 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?
>
>
> Hi Bob:
> Your comments above are correct, and the Rev B circuit will work.
>
> BUT...

---  snip ----
> degrees
>
> By integrating across 180 degrees in Rev B, versus just 90 degrees in
> Rev.A you are incurring an additional 2 dB reduction in gain and increase
> in NF in the Rev B. mixer, assuming the implementation losses of both
> circuits are the same.

Right.  That is why Horton ISD is so ugly and complex looking.  I was 
trying to get each turned on for 90 degrees at a time.  I think we 
should just test the simpler circuit.  We can tolerate the 2 dB 
insertion loss if the input to this mixer is presented to a front end 
based on (say)  the Norton amplifier Ulrich has shown us as one 
example.  Should we implement that in a push-pull circuit,  we would 
have a front end with 40 dBm IP3,  great IP2,  large dynamic range and 
too good a noise figure for HF.  You could then warm the front end up 
with IP3 improving loss and have a great front end with better 
performance than we can use on HF but would still be usable in overtone 
mode on VHF bands.  I think the loss from the simpler mixer circuit is 
therefore easily overcome in a full system.  The front end amplifer, if 
based on the Norton design from Ulrich or something similar, will also 
provide isolation which aids in preventing LO, etc. leakage back to the 
antenna.  So in a full system,  there is a good symbiotic relationship 
with a slight compromise on the mixer for simplicity and a decent front 
end (serving multiple system purposes).

Just my opinion.

Best 73's
Bob
N4HY

>
> If you wanted to simplify the receive circuit, using just one 4:1 mux
> in a single balanced circuit would probably work just as well, with
> possibly lower implementation losses.
>
> Best regards, --- Graham / KE9H
>
> ==
>
>


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