[time-nuts] GPS antenna setup: how good?

Bob Camp lists at rtty.us
Wed Mar 24 23:22:13 UTC 2010


Hi

At least back a while ago, GDOP and TDOP values as reported didn't have quite as strong a correlation as I would have expected them to have. I haven't done that in a while so things may be better with more modern receivers.

Bob


On Mar 24, 2010, at 7:11 PM, Tom Van Baak wrote:

> Hal,
> 
> That's a really good question and if anyone can point me
> to carefully performed measurements already done, I'd
> appreciate it. It could be antenna A vs. antenna B, or it
> could be antenna A with vs. w/o ground plane, or choke
> ring, or radome, or temperature stabilization, etc.
> 
> For short-term effects looking for an improved RMS value
> of the internal GPSDO "TI" numbers would confirm that
> the antenna is better. An hour of data should suffice. Or
> forget GPSDO locking and just look at 2D or 3D position
> scatter in survey mode. Mark has done nice work here.
> 
> For long-term effects you'd look for an improved 1 hour
> or 1 day RMS value (or ADEV) in a comparison between
> the GPSDO output and suitably stable house reference.
> A couple of days of data would is probably be enough to
> detect A vs. B differences.
> 
> I'm not sure signal strength by itself is the key. I would
> think quality of the signal (multi-path) is more important.
> Maybe there are other factors. But the bottom line is how
> much, if any, better the output 1 PPS or 10 MHz is.
> 
> If you had a set of many days of data with and without
> (pie pan, ground plane, choke ring), then you could
> correlate the 10 MHz output deviations (vs. house ref) with
> any number of parameters and confirm or deny if signal
> strength, Az-El, time of day, or temperature had anything
> to do with measurable performance.
> 
> /tvb
> 
> ----- Original Message ----- From: "Hal Murray" <hmurray at megapathdsl.net>
> To: <time-nuts at febo.com>
> Sent: Wednesday, March 24, 2010 10:59 AM
> Subject: [time-nuts] GPS antenna setup: how good?
> 
> 
>> How do I tell which of two setups is better?  For example, how much does adding a pie pan help?
>> Is there some simple parameter I can look at that tells me an antenna goodness value?  If not, what's a reasonable recipe to come up with a number or compare two antennas?
>> What's the appropriate time scale to use when thinking about that problem?
>> I haven't (yet?) looked at any of the satellite position and signal strength data.
>> Can I do something like wait until a satellite is about to go directly overhead and plot the signal strength while occasionally swapping the antennas?  Are the signal strength readings reasonably noise free and/or repeatable from run to run which may be a few days apart?
>> Assuming it goes high overhead, how long is a satellite within view?  (ballpark)
> 
> 
> 
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