[RFI] Polarity Tests -- Great Work, Wrong Word

[Jim Brown]

Thanks for the great work, but you're using the wrong word to describe 
it. The correct word is "polarization," which describes the orientation 
of a field in 3-dimensional space.  We most often control the 
polarization of a field by the orientation of the antenna that produces it.

"Polarity" is the positive or negative sense of the waveform. We change 
polarity by reversing the pair of wires carrying a signal, or by passing 
it through an inverting gain stage. Historically that has WRONGLY been 
called "phase."  It is NOT phase -- phase is a continuously variable 
function and is measured in degrees.

The effects of phase and polarity are VERY different.  Phase varies with 
frequency, time, and the nature of the electrical circuit (including 
antennas) that carry a signal. Phase is defined for a single frequency.  
If, for example, we add a length of line to provide a 180 degree phase 
shift, the phase shift is different at every frequency. If, however, we 
reverse the sense of the signal, the result is that the two signals 
cancel at ALL frequencies (provided that the antenna doesn't also modify 
the phase, which it often does).

73, Jim K9YC

On Tue,6/13/2017 10:48 AM, Tom Thompson wrote:
> Some of you have mentioned in the past about using a tuned loop for 
> tracking RFI.  A question has sometimes arose about the direction of 
> the null of the loop.  Larry Benko, W0QE, and I did some polarity 
> tests using various orientations of both the transmitting short dipole 
> and a receiving loop and a receiving short dipole. The results are 
> shown here:
>
> http://tomthompson.com/radio/Antenna_Polarity/Antenna%20Polarity%20Measurements.html 
>
>
> 73,   Tom   W0IVJ
>
>
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