[time-nuts] Trueposition Antenna Location

[Bob kb8tq]

Hi

There are lots more issues to GPSDO stability than just antenna placement. Indeed
you are correct that a location that keeps you out of holdover is a must. Ideally you
want to be able to lock on to 4 sats at all times. That generally equates to being able
to “see” something in the > 6 range all the time. Once you get the antenna set up
well, you can start fiddling with the rest of the normal GPSDO issues. 

Equally, there are a bunch of qualifiers any time you do an ADEV measurement. The
most basic is that it’s a comparison. You get the combined ADEV of your two standards.
That’s fine if you have a hydrogen maser and are looking at a GPSDO :). Comparing one
GPSDO to another will always get into the “which one is better?” debate. 

One way to separate data is by comparing three devices. That assumes you *have* three
fairly good devices to compare. In this case a reasonably good OCXO could do the trick. 
If a telecom Rb is handy, it also would be a good thing to toss into the mix. 

All that said, there are GPSDO’s out there that will plot out roughly an order of magnitude
better than what you are seeing. That’s when they are compared to something much
better (and it drops out of the plot). 

Bob

> On Nov 29, 2018, at 11:22 PM, Mark Goldberg <marklgoldberg at gmail.com> wrote:
> 
> I have one of the TruePosition GPSDOs. They already are not the best in
> terms of signal sensitivity, but the antenna is now located where it sees a
> narrow segment of open sky. It generally sees no more than 4 or 5 sats and
> goes into holdover often.
> 
> I just use the 10 MHz output as a frequency reference.
> 
> Attached, (hopefully if I did it right) are images of the Lady Heather
> screen and an ADEV plot referenced to a Bodnar GPSDO.
> 
> How much could I expect ADEV to improve if I move the antenna to a better
> location with clear view of the sky? The things I am testing need to be
> better than 8e-10, so this at just under 3e-10 may be "good enough". Moving
> the antenna would involve drilling a hole in the outside wall, so it is not
> easy.
> 
> Any suggestions are welcome.
> 
> Thanks,
> 
> Mark
> <TruePos2_Heather.png><TruePos2_Allan.png>_______________________________________________
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