It is not just the modulation that must be matched it is the carrier phase.
If you use separate transmitters it is likely that they will not be on
exactly the same frequency, nor would their phases be locked even if they
did end up on or near the same exact frequency. This would result in
periodic signal cancellation the same as happens on vhf with mobile stations
having multi path problems.
IF you you the same transmitter and simply split the power then you can
calculate the directivity changes with any decent antenna modeling program.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
> -----Original Message-----
> From: Jari Jussila [mailto:jari.jussila@oh2bu.pp.fi]
> Sent: Sunday, August 14, 2011 16:25
> To: towertalk@contesting.com
> Subject: [TowerTalk] Two signals on the same frequency?
>
>
>
> A hypothetical question:
>
> I have two antennas for the same band. The antennas might be
> same kind
> (eg. two dipoles, two yagis) or different (one dipole, one vertical).
> I transmit with two separate transmitters - one to one antenna - but
> modulate the transmitters simultaneousl*y *with same key or
> microphone.
>
> How does my signal-strength change on the other side in
> comparison if I
> used only one transmitter and one antenna? The antennas are
> not phased
> to each other and they might be quite apart from each other.
>
> 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?
>
> Jari, OH2BU
> _______________________________________________
>
>
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