[time-nuts] Req: Decent GPS AntennaActive/Passive Recommendation

Bob Camp lists at rtty.us
Mon Sep 16 11:38:41 UTC 2013


Hi

Once the sat's all arrive at the antenna, a fixed delay (in general) does not impact things a lot. The gotcha with the filter is that it's delay is unequal across the GPS band. Doppler puts the sat's all over the place. That gives some more delay than others. Having unequal delay on sats is indeed an issue. As the filter changes delay with temperature things will move a bit more.  Since it's a "frequency high on approach / low on departure" sort of thing it will average out on each pass. The main impact would be an increase in wander.

Bob

On Sep 16, 2013, at 1:24 AM, David J Taylor <david-taylor at blueyonder.co.uk> wrote:

> From: Bob Camp
> 
> Hi
> 
> All of the ones I've opened up or seen dis-assembled have had the ceramic plate antennas in them. That very much surprised me early on, since I *assumed* they had something fancy inside based on their shape.
> 
> No argument about the filtering, I'm not sure if the temp-co of filter delay on an exposed antenna makes it a plus or a minus….
> 
> Bob
> ===================================
> 
> .. and would the true time-nut add the delay through the filter to the delay in the feeder co-ax?  I suppose that means you could only buy an antenna with a stated, calibrated delay?  Limits the choice, a little!
> 
> Cheers,
> David
> -- 
> SatSignal Software - Quality software written to your requirements
> Web: http://www.satsignal.eu
> Email: david-taylor at blueyonder.co.uk 
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