[linrad] Re: MAP65 Experiment

["Joe Barger" <aero.org; barger@xxxxxxxxxxxxxxxx>]

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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