[TowerTalk] Two signals on the same frequency?

[Jim Brown]

On 8/14/2011 3:05 PM, K8RI on TT wrote:
> Even then the signals remain synchronous only if they travel equal
> distances to the antennas.

You're confusing phase and synchronous. Different.  Synchronous means 
that they have PRECISELY the same frequency and modulation.  For 
example, when a radio signal is detected in many channels of a 
multi-channel audio mixer,  the detected audio will be synchronous. If 
it is equal in all channels, the summed audio will increase by 6dB for 
each doubling of the number of channels added together. By contrast, 
non-synchronous (random) signals of equal strength add by 3dB per doubling.

When RF gets into equipment as RFI, it often enters by multiple paths, 
and these paths can have very different gains and phase shifts. Thus, 
the STRENGTH of the coupled RF signal can vary by as much as 30-40dB 
over a wide range of frequency. There's a lot of measured data on my 
website in various AES papers dedicated to RFI.

K1TTT's point regarding phase shift in amplifiers is important to the 
extent that it can change the pattern, but it does not make the signals 
non-synchronous if they come from the same transmitter.

73, Jim K9YC