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

["Björn"]

Hi Bob,

Doppler shift is +-3.5kHz.
Bandwidth for the CA signal is ca 2MHz, narrow correlator receivers takes
in >10MHz to mitigate multipath errors.

So doppler spread is about 1/1000 of the spread spectrum signal. Does the
filter delay really change that much with 7kHz total doppler variation?

For Glonass receivers this is more of a problem, since Glonass is a FDMA
system.

--

     Björn

> 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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