[hpsdr] Odyessey-Siren Rev B.

[Ahti Aintila]

Graham,

Thank you for reminding. I forgot that I'm using two SPDT switches or
actually four switching transitions. Same as in the 90 degree
solution.

However, I need more time to think and understand Dan's explanation.

I have not measured the carrir leak, but that should be easy to
control with a careful and balanced construction of the circuit. The
switches seem to be very well balanced.

73, Ahti OH2RZ


On 19/12/06, Graham Haddock <grahamh at verizon.net> wrote:
>  > 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
>
>
> Hi Ahti:
>
> The 2 dB difference in gain and Noise Figure between 90 degree
> sampling and 180 degree sampling is mathematical, and includes no
> implementation losses.  Implementation losses could increase
> or decrease the difference.
>
> The number of switching transitions are the same for 180 degrees
> and 90 degrees sampling, that is, one ON and one OFF per cycle.
> The only difference being how long the time between ON and OFF.
>
> I include part of an email discussion (below) with Dan Tayloe, N7VE,
> as a part answer for your "theoretical truth."  It should be very easy to
> verify in a SPICE simulator with ideal switches, and compare the ratio
> of input signal level to the output level.
>
> ====
>
> Dan Tayloe, N7VE wrote:      [softrock forum Dec 14/2006]
>  > ... .
>  > The primary difference in detectors is the type that samples
>  > 180 degrees, half an RF cycle onto detector cap, and the type
>  > of detectors that sample a quarter an RF cycle onto a
>  > detector cap.
>  >
>  > ... .  In theory, a half cycle sampling gives a 3 db
>  > conversion loss as it averages half a sine wave onto the
>  > detector caps. The quarter cycle RF cycling detector in
>  > theory produces a 1 db conversion loss. Think of the average
>  > of the 1/4 cycle sine wave peak producing 0.9x of the peak
>  > input voltage. This voltage loss is not readily viewable,
>  > since the loss is across the source impedance.
>  >
>  > In theory, sampling 1/8th of a cycle would improve
>  > sensitivity even further, but after you get to 90%, there is
>  > not much reason to go further. In addition, you would need to
>  > figure out how to put back together 0, 45, 90, 135, 180, 225,
>  > 270 and 315 degree outputs.
>  >
>  > - Dan, N7VE
>
> ====
>
> Your particular circuit might not favor 90 degree
> sampling, because in that case, each half of the differential
> input transformer would be unterminated for half of the time,
> Simply switching from 180 degree switching to 90 degree
> switching may not work well in your circuit.
>
> I agree that 2 dB reduction in gain and NF would
> not be noticeable on HF bands.  I thought that SIREN was
> being designed for IF for VHF/UHF receiver, and the extra
> 2 dB gain and NF might be welcomed, or perhaps not.
>
> Your circuit may have an advantage on the transmit side,
> because of the differential transformer.  Have you made
> any measurements of the (switching) carrier leak through
> on this design?  As compared to the original QSE design?
>
> My best regards, --- Graham / KE9H
>
> ==
>
> >
>
>

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