[time-nuts] GPS shielding by power lines?

David McGaw 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.

David N1HAC

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
>same result.
>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.
>Alan G3NYK
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