[Amps] new amp race (RFI polarization)

[Manfred Mornhinweg]

Tom,

> I have tracked down a lot of man made RFI (mostly from grow light 
> ballasts) and without exception the signal is vertically polarized until 
> you get very close to the source.  I found this very interesting,

I do find it interesting too. I never made such tests - I was just 
applying theory.

> so a 
> friend and I used a battery powered oscillator with an end fed 
> horizontal wire for an antenna.  We placed it horizontally on the floor 
> of his house on the second floor, the first floor, and finally in the 
> basement.  The signal was always vertically polarized on 40m until we 
> got very close to the source.

Stop for a moment. An end-fed antenna, and a battery-powered oscillator? 
Where did the other pole go??? You surely know as well as I do that 
current flows betwen two poles. An end-fed antenna is usually fed 
against ground, or against a counterpoise. The entire antenna system 
comprises the antenna, the ground or counterpoise, all wiring between 
them, and any other nearby conductors coupling to the system by 
capacitance, mutual inductance, or both. We need to find out how all the 
house interacted with your oscillator and antenna, when you made that test!

And even if your end fed antenna had been radiating a purely horizontal 
signal, placing your receiving loop higher or lower at an azimuth angle 
aligned with the antenna would produce a vertically polarized signal at 
the receiving antenna.

 > I was using a tuned loop antenna for
> receive.  I had previously determined that the null looking through the 
> loop indicated vertical polarization, whereas the peak looking  through 
> the loop indicated horizontal polarization. 

Stop for another moment! A loop antenna held in a vertical plane has a 
horizontal magnetic axis. So its polarization is vertical when seen from 
the side, and horizontal when seen from above or below. And 
mixed/slanted when seen from another angle. The directivity is such that 
looking through the loop, along the magnetic axis, is a null. Maximum 
reception is equally from the sides, from above and from below. If you 
point the magnetic axis of the loop at the signal source, in theory you 
should receive nothing. Anything you do receive is by reflections, and 
the loop responds to vertically polarized signals bouncing in from the 
side walls or vertical objects, and horizontally polarized signals 
bouncing in from ceiling, floor and horizontal objects.

And all of this is true only if the wavelength is short enough! 
Direction-finding HF signals inside a building, and testing their 
polarization, is pretty hopeless, because the wave is typically longer 
than the free spaces, and you get a very complex mess of local electric 
and magnetic fields rather than a well developed, well defined wave!

Manfred

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