After reading the "Polarization question" thread that Joe started,
reviewing the WSE architecture, and thinking about the problem more, my
quick and dirty approach to getting linrad/MAP65 with polarization
probably won't work. Calibration using Dphi may compensate for initial
phase errors between the two RX channels, but the phase errors
introduced by the SDR-1000 (and transverter) LOs drifting at different
rates would quickly degrade performance. Using the same (low phase
noise, etc.) clock for each conversion stage appears necessary to
preserve phase information. Probably obvious to those who have thought
about this for more than a microsecond, but ...
WSE is really nice solution, but with one kid in college and another
close behind, it's a bit out of my price range at the moment. There's
an external 10 MHz frequency input for the SDR-1000 so both SDR-1000s
can be run from the same frequency reference, but I'll have to
investigate potential transverter/down-converter solutions. What
hardware are others using to solve the problem?
joe n6kk
----- Original Message ----- From: "Joe Barger" <barger@xxxxxxxx>
To: "Linrad mailinglist" <linrad@xxxxxxxxxxxxxxxxxxxxx>
Sent: Thursday, July 26, 2007 3:51 PM
Subject: [linrad] MAP65 Experiment
I'm thinking about how to easily adapt my EME station to take
advantage of MAP65, initially receive only.
The receive side my station consists of two phased yagis, preamp,
Elecraft 144 transverter, and SDR-1000. I'm considering removing the
power splitter, rotating one of the yagis 90 degrees and duplicating
the receive components to have duplicate H and V RX paths.
My main questions involve how closely the two RX paths must match in
amplitude, phase and frequency. Amplitude I can probably adjust
reasonably well in the SDR-1000, and I can probably adjust the RX
frequency in both SDR-1000s to initially be pretty close, but the
SDR-1000s are not locked to the same LO so they will drift apart after
some period of time. In addition, the relative phasing will be
unknown and probably also change over time. Hopefully amplitude will
remain fairly stable.
I think Dphi will compensate for initial phase errors between the
channels, but how sensitive is the system to drift between the two
SDR-1000 LOs (and corresponding phase and frequency errors)? I think
the SDR-1000s (and transverters) will stay within a couple hundred
hertz of each other for a reasonable period of time, but if the
relative frequency and phase in the two channels must stay locked to
within a few hertz/degrees then I think there is no hope with this
approach. I'll probably just have to wait for a couple of the HPSDR
Mercury boards ... or buy another SDR-IQ (if the LOs can be locked ...
I don't remember if they can).
If this hardware approach works, the next issue will be how to get two
instances of PowerSDR, one linrad and one MAP65 all working happily on
the computer resources I have ...
Thanks
joe n6kk
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