[TowerTalk] Two signals on the same frequency?

[Andy]

> A hypothetical question:

Not exactly tower related.

Two signals on the same, or nearly the same, frequency can add
together either constructively (in phase) or destructively (out of
phase).

If the two signals (their RF signals, usually starting with an xtal)
are phase-locked to one another, then it is just like having one
transmitter, split to two antennas.  Then the results are what we
expect for a phased array.  More signal in some directions, less
signal in other directions.

If the two signals are not phase-locked, then their frequencies will
differ slightly ... their signals will drift in and out of phase, at a
rate that depends on the amount of frequency difference, no matter how
large or small that difference is.

For any person listening, in any direction, they will hear your signal
going stronger, then weaker, and so on, as the signals change between
adding constructively and destructively.  They will hear the "beat
frequency" between the two transmitters.

When the two signals add constructively, the signal strength will be
stronger than one transmitter alone.  When adding destructively, the
signal strength will be lower, maybe even zero.

> I know that the advanced contest stations have one beam to eg. JA and
> one to Europe etc.  But if they turned both antennas to JA, would the
> signal-strength go up?

If phased properly, yes.  It is a phased array.

Andy