GPS issue related to GPS antenna selector ?

Joerg Reisenweber joerg at
Sun Jul 13 23:27:52 CEST 2008

Am So  13. Juli 2008 schrieb Philippe Guillebert:
> Hello,
> Thanks to , I 
> ran into the following (and quite scary) thread : 
> So I was wondering, maybe the poor GPS performance issue many FR seem to 
> have, especially on the internal antenna, is related to the GPS antenna 
> MUX (the part responsible for the switch between internal antenna, and 
> external antenna if you hook one up) selecting the external antenna, 
> even when there isn't one ?
> The randomness of this issue could be explained because driving the mux 
> with levels like 26% Vdd is kind of "grey zone" and can result in some 
> devices working as expected and some selecting the ext. antenna without 
> one and then having bad reception.
> I see one way to test this theory, by driving the select signal VCONT to 
> 0V (Werner Almesberger talks about shorting R7616) and see if this 
> improve reception on the internal antenna.
> This is pure speculation, I didn't test anything and perhaps that's just 
> plain stupid but I'd love to hear from someone that focused on this 
> issue back in April.

IIRC Andy did all of these tests and found they didn't solve or even alter the 
symptoms (see later posts in same thread).
Though the circuit design is definitely flaky, it doesn't seem to trigger any 
of the suspected problems.

Anyway thanks for the feedback
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