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" <[EMAIL PROTECTED]>
To: "Linrad mailinglist" <linrad@antennspecialisten.se>
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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