[time-nuts] GPS shielding by power lines?
david at endor.com
Mon Aug 11 00:12:35 EDT 2008
You didn't say if you tried the antenna under the power lines but
outside the cabin. What is translucent to light may not be to microwaves.
At 05:15 PM 8/9/2008, you 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). We extended the cable and moved
>the antenna about 20 - 30 feet to the side of the line run, which was
>mounted on wooden poles at about 25 feet. In this position we immediately
>got a reliable fix. The fix and number of usable satellites degrades as we
>move nearer the lines.
>The thought was that there as interference arcing or corona noise from the
>line insulators, and a receiver (AM) was deployed to listen for what was
>expected to be a substantial wide band noise signal....we didnt hear one! We
>are now confused about what the effect is. The signal could not be
>"screened" by the wires which are about 3 feet apart, but they definite
>provide a cone of interference directly under the run. The experiment was
>later repeated with two further different GPS receivers and produced the
>Has anyone seen this before? have you any idea of what level noise we should
>be looking for? I believe this is a wide signal so maybe an AM receiver is
>not the best choice The area is a rural, horticultural area (called market
>garden in the UK) We are obviouslt concerned to trace any noise sources in
>the vicinity of the Hydrogen line frequency at 1420MHz.
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