Re: Power line interference?
From: Bob Greschke (bob_at_greschke.com)
Date: 07/12/04
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Date: Sun, 11 Jul 2004 21:03:07 -0600
I've worked around large power lines in places like along the San Bernardino
river in Los Angeles and I never noticed any problems with my handhelds.
These receivers are connected to the recorders with a 6-conductor cable, so
while the coax theory is correct it doesn't apply here.
Thanks!
"Robertwgross" <robertwgross@cs.com> wrote in message
news:20040709141828.12055.00001669@mb-m01.news.cs.com...
> Bob Greschke wrote:
> >We have a seismic station described on this page
> >
> >http://www.passcal.nmt.edu/~bob/passcal/catscan/catscan12.htm
> >
> >See the power lines overhead in the first picture? As the weather has
> >gotten warmer in Italy the GPS (used for timing) has gotten fewer and
fewer
> >satellite locks. It's down to one a week now (the clock tries to lock up
> >every 20 minutes). It's quite well correlated with the gradual increase
in
> >temperature inside the building over the past 50 days (the recording
system
> >records its own temp -- now in the low 20's C). Do you think an increase
in
> >electricity demand creating a stronger magnetic field could do it, or is
the
> >GPS antenna (which also houses the GPS board itself, and that is on top
of
> >the building) just getting flakey with the heat? The power lines are a
good
> >5 or 6 meters above the building. I don't know what the voltage is.
When
> >the station was installed I was more concerned about the 50-60Hz signal
> >getting induced into the seismic data than causing the GPS any trouble.
>
> I've been down this road before! First of all, you can forget about the
power
> lines. I've seen lots of interference into GPS before, but never from a
power
> line. An external antenna can go bad, but that is not terribly common. The
> receiver inside can go bad, and that varies by brand, model, and who
installed
> it in the first place. The coaxial cable connecting the antenna to the
receiver
> accounts for more than 50% of the problems. Some coaxials are installed
with
> too much tension. Over time, the center conductor contracts due to heat,
and
> that can pull the connection apart. In some cases, when the connection is
> pulled apart, and the DC flow to the antenna is stopped, then everything
stops
> until it cools off. In some cases, the lightning protector is the culprit.
> That's easy to replace also. Some connectors are crimped, and others are
> soldered. A bad crimp job or solder job will stop everything.
>
> Been there. Done that. Wrote the book. Made the video tape.
>
> ---Bob Gross---
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