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

[Tom Van Baak]

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)