[time-nuts] GNSS antenna delays

[Bob Camp]

Hi

There are a lot of variables in all this. If you have a good antenna, it’s got a filter ahead of
the preamp. It may also have a filter after the preamp. Just how wide these filters are …
that depends. If you grab a bunch of SAW filter data sheets, you see numbers in the 10 to 25 ns 
range. Older ceramic resonator filters are a bit hard to pin down. 

Bob

> On Jun 29, 2016, at 5:46 PM, Michael Wouters <michaeljwouters at gmail.com> wrote:
> 
> The discussion about antenna cable delays made me think of the issue of the
> antenna delay. An antenna typically has a bandpass filter and amplifier so
> there clearly is some non-negligible delay associated with this.
> 
> The issue is usually sidestepped by calibrating the delay of
> receiver+antenna (against what? A calibrated receiver + antenna from
> the BIPM of course...)
> 
> But sometimes, after calibration, an antenna in the field has to be
> replaced with a different antenna and the original calibration is
> invalidated. It then becomes necessary to expand the uncertainty of the
> delay.
> 
> I did read a NIST paper where they described measuring the delay by
> physically disassembling the antenna so that they could feed signals
> directly to the electronics. Delays like 30 ns were measured, I think.
> Myself, when changing antennas I have seen steps like 10 ns.
> 
> Does anyone have any data points to add to this ?
> 
> Cheers
> Michael
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