[time-nuts] GPS shielding by power lines?

[Alan Melia]

Hi Dave, Ah I meant a 1600Mhz AM RX not a MW job the resuly is quite
dramatic from seeing no usable satelites to seeing 10 to 12. The software we
are running plots the tracks of the those sats seen so we can see that when
seen even close to trees, foliage shielding is not a problem. I could post
this plot over a number of hours it is "very pretty", and shows clearly the
northerly extent of the orbits very clearly.

Thanks Magnus for thoughts on further tests. We are logging the NMEA
sentences so most of that detail could be available. A job for a laptop I
think.

Alan G3NYK
----- Original Message -----
From: "David Ackrill" <dave.g0dja at tiscali.co.uk>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Sunday, August 10, 2008 8:30 AM
Subject: Re: [time-nuts] GPS shielding by power lines?


> Alan Melia wrote:
> > Hi all,  in the process of setting up a GPS time standard for a Radio
> > Astronomy facility (amateur) we installed a GPS receiver in a small
cabin
> > with a translucent roof, thinking that would not impede the GPS signal.
> > After a lot of head scratching as to why we were not getting the
performane
> > we got at another site, we realised that the "convenient position" for
the
> > cabin was directly below a three phase 11kV power distribution line (
common
> > UK rural electricity distribution system).
>
> Since the satellite signals are in the high UHF range, arround 1575MHz,
> the AM receiver test is not going to tell you alot about the noise at
> the frequency that the GPS receiver is using.  So, even if you had
> detected any noise from the overhead lines, it might not have been proof
> that this was the cause of the problems.
>
> I find that the positioning of the antenna for a GPS receiver can be
> very touchy.  You really need a good view to the horizon and, despite
> what you might see on simple presentations of the satellite positions,
> they do tend to be mainly in the southern sky when viewed from the UK.
>
> See
> http://www.guralp.com/articles/20060405-howto-gps-troubleshooting/print
> for details.
>
> The other effect that you may notice is that your 'good' position for
> the antenna isn't so good all of the time as the satellites appear to
> move round the sky and the signal strengths from each alters.
>
> Dave (G0DJA)
>
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