When two tones (RF or audio) are at exactly the same frequency, they are
"zero beat" with each other. They could be at any phase relation to each
other, so the amplitude of the sum of the two could be anywhere from
twice that of one of them or zero. Without careful amplitude adjustment,
the two tones will not be equal, so twice the amplitude, or zero, will
seldom occur. Even with careful amplitude adjustment the phase relation
will seldom be exactly zero or 180 degrees, so double amplitude or zero
amplitude sums will still be rare.
Having said all of that, the sum is just as likely to be lower amplitude
as it is to be higher than that of either single tone.
James Duffer wrote:
snip
When the "cw" button is pushed you get a sidetone. While holding down
this button you move your dial until your target's tone is "beating"
against your sidetone. When you move the dial enough so that your sidetone
no longer "beats" and the tones are "insync" they become "one". When two
tones become "one" the tone gets louder. This is "zero beat". Even having
just "beating" is close enough for govt work.
snip
For many years I have been under the impression that "zero beating" was the
method of beating (hetrodyning) of two frequencies bringing their difference
down to the audible range and adjusting one to match the frequency of the
other so that the two tones beat against each other producing "zero" out.
Thus the term zero beat. Not a louder tone.
de wd4air
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