[TowerTalk] Two six meter antennas

[jimlux]

Drax Felton wrote:
>  
> 
> Assuming that they were both pointed in the same direction.
> 
> If one were to connect two six meter beams, on separate towers, together
> with a Tee connector onto one radio what would the outcome of this be on
> receive?   Would you get additional gain or distortion since the coax runs
> are of different random length?
> 
>  
Gain yes, distortion no.Oddball pattern, certainly.

What you're building is an interferometer.  The pattern will have a 
bunch of narrow lobes looking sort of like a leaf rake.

Assume the coax is exactly the same electrical length and the antennas 
are 24 meters apart (4 wavelengths). Free space, no funky multipath.

Directly on boresight, the signals from the two antennas are in phase, 
and add, giving more gain.  Now, move off boresight by 1 degree. Now the 
signals arrive at the two antennas slightly out of phase (by 
360*sin(phi)*spacing/wavelength or 360*sin(1)*4 or about 25 degrees).. 
so the signal into the radio isn't quite as big as it was when it was 
perfectly in phase.

Move a bit more off boresight, to where the signals are out of phase.

sin(phi)*360*4 = 180 --> sin(phi)*2*4= 1 --> sin(phi) = 1/8  -> about 
7.1 degrees..

At that point, you have a sharp null.  Move more.. to 14.2 degrees off 
boresight, and the phases line up again, you have a peak.  Basically, 
you get this repeating pattern of peak/null, with a period of 14.2 degrees.

Space the antennas farther apart, and the period decreases.