[time-nuts] GPS Antenna -Receiver Mutual Interference...
Mark J. Blair
nf6x at nf6x.net
Mon Jan 3 22:47:02 UTC 2011
On Jan 3, 2011, at 1:00 PM, Burt I. Weiner wrote:
> I'm not sure of the nature of the two receivers, but using conventional receiver design thinking, the only thing that comes to mind that might be radiating would be the oscillators or possibly the I.F. section taling to each other.
My company's earlier GPS receivers used a frequency plan with the IF at around 2 MHz, so the LO was well within the passband of the SAW filter and common patch antennas (both typically have passbands around 5 MHz wide, IIRC). Thus, we had quite a bit of LO leakage then. While our own receivers generally didn't mind sharing an antenna through a simple splitter, we tended to have trouble when doing this with a mixture of our own receivers and some of our competitors' receivers. Some combinations apparently resulted in LO leakage from our receivers causing problems for our competitors' receivers. While there's something to be said for jamming one's competitors, this prevented us from gathering the comparative data that we needed. :) We fixed this with the simple expedient of putting an attenuator on each splitter output to reduce cross-coupling.
I haven't been directly involved in receiver testing for a while, but I think that we now use a higher IF, and thus I'd expect that we get a lot less LO energy leaking out through the front end.
In any given setup involving multiple GPS receivers sharing an antenna and/or located close to each other, you may or may not have problems. It'll depend on the particular combination of receivers, the LO frequencies, how much LO leaks out of each one, whether that LO leakage lands in a bad spot for any of the other receivers, how much isolation is between the receivers, etc.
Mark J. Blair, NF6X <nf6x at nf6x.net>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.
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