[hpsdr] Odyessey-Siren Rev B.

[Ahti Aintila]

On 19/12/06, Graham Haddock <grahamh at verizon.net> 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?

Hi Graham,

When deciding to use 180 degree switches, the circuit simplicity and
power saving were the primary concerns in my mind. Any possible 2 dB
noise figure increase on the fixed IF frequency, or even across the
whole HF spectrum, doesn't mean very much.

On the other hand, due to the non-ideal switches (unsymmetrical
switching delays, rise times) there are double number of lossy
switching transitions per time with the 90 degree solution than the
suggested 180 degree configuration. When optimizing all other
parameters (especially the impedance match) for the corresponding
case, the losses in my limited experiments indicated slightly lower
losses with the 180 degree switching.

Using ideal components, I think, the both configurations should be
equal. This is only my layman's understanding and findings so I may
have made some mistakes in my measurements. Also the comparisons
naturally were made with different switches that possibly had
different on-resistances.

Are there any mathematicians around to tell the theoretical truth?

73, Ahti OH2RZ

>
> 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

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