Topband: Polarity and Phase

[Jim Brown]

>Phasing the receiver audio output is absolutely no different that phasing
>two antennas, and flipping one speaker lead is no different than flipping an
>antenna phase 180 degrees. 

You are absolutely incorrect! First, you don't understand (or are
unwilling to admit) that phase and polarity are different. When you
reverse the wires that connect elements of a system (e.g., a receiver,
transmitter, loudspeaker, microphone, or a dipole), you are changing
the polarity of the system. When you change the spacing between
antennas, or the length of a feedline between elements of an array, you
are changing the phase, but you are not (usually) changing the
polarity.  What's the difference?  Well, obviously, the feedline will
be a different electrical length, and thus produce different phase
shift, at every frequency. We know, of course, that the phase
relationships are a big part of what produces the patterns of our
antenna arrays.  

Example -- the 180 degree out of phase azimuth(s) for a an array of
vertical antennas ARE, indeed, where the null(s) will be. But the
radiation from the elements of the array will ALSO be out of phase with
each other in every other direction, and to a varying degree. In these
directions, the pattern will be some intermediate value between its
peak and its null -- as the phase between the signals from the array
elements varies CONTINUOUSLY. And we know that we can change the
azimuths where the nulls are by varying the phase shift -- the length
of the feedlines, the spacing between the antennas, and the azimuth
between the array elements.  In this paragraph, every use of the word
"phase" is correct. In your sentence, quoted above, the first use of
"phasing" appears to mean "polarity," the second use is not clear, and
"flipping one loudspeaker lead"  means inverting the polarity. 

When you write carelessly like this, you confuse people, and you also
tend to muddy the thinking of folks who are trying to learn. More
important, the sentence quoted is technically incorrect, even if we
were to rewrite it substituting "polarity" where you mean it.  This
difference is at the crux of why it is so difficult to get good
broadband performance from a directional array. I learned this as a kid
when I drove through the nulls of a 4-tower AM directional antenna
system a few miles from my home. The null for the carrier was deeper at
a different azimuth than for the sidebands. The phase shift WAS 180
degrees at the null for the carrier frequency at some point, but it was
a different number of degrees at the frequency of the audio sidebands,
and their cancellation was far less.  Those phase relationships were
NOT created by "flipping" wires -- they were carefully created by the
antenna spacings, their physical locations, the length of the feedlines
between them, and even phasing networks. 

>Unless every receiver oscillator is common to each other you can accomplish
>the same thing as shifting polarity OR phase by slightly tuning the dial of
>the receivers or any oscillator in the receiver. If the oscillators are not
>forced to lock with each other or common oscillators in a fraction of a
>second they will be out of phase (and "polarity") in a few seconds.

This is also incorrect. When you the oscillators (in a CW or SSB radio)
are on different frequencies, you are "uncorrelating" the signals, and
"phase" has no meaning. When they are free running but fairly stable,
you may, by some happy accident, be able to get them close (even rather
precisely) to the same frequency. 

The use of "phase" when we mean "polarity" is an unfortunate
anachronism, and laziness, and it confuses people. Yes, when you and I
grew up, it was common usage. But as engineering has matured, we have
learned to use the right word to describe polarity separately from
phase. 

There is also the issue of time. Add some delay, and you have added
phase shift that is directly proportional both to time and frequency.
This is not polarity either, nor is it phase. It is time. 

Polarity is not a function of space, or of time, or of frequency. These
are fundamental concepts, and understanding how they interrelate is key
to our understanding of how antennas (and lots of other systems) work.
It is unprofessional to make that understanding more difficult by using
the wrong words to describe what's going on.

Jim Brown K9YC