[time-nuts] GPS shielding by power lines?

[Thomas A. Frank]

> 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


Alan;

I have no idea if this is a cause of your problem, but in some work I  
have done, I found that the high field strengths (electrostatic and  
magnetic) found under power lines can adversely effect electronic  
equipment that should otherwise be unaffected by the presence of  
power lines and their low frequency signals.

I would imagine that the fields could desensitize receivers by  
overloading the front end amplifiers, and no amount of filtering is  
going to help because it is virtually impossible to shield against  
50/60 Hz signals.  A solid steel conduit several mm thick is only  
good for about 27 dB attenuation at power line frequencies.

Fortunately, distance makes things better, so you may just have to  
move everything a bit away from the power lines.  Our solution was to  
digitize our signals several hundred meters from the power lines and  
send the results digitally past them.

Try getting a field strength meter (gaussmeter) and see what levels  
you have under the lines.

Tom Frank, KA2CDK