[Moon-net] Feeding question

[Alberto di Bene]

Gerd wrote:
> Hi everybody,
> 
> I think that´s an interesting discussion, let me add this:
> 
> The system N/F will be considerably lower due to the fact
> that the noise from the two preamplifiers is of random nature
> (non coherent) and will (at least partially)  be cancelled at the
> combiner.  While the signals from the antennas (coherent) will
> add (in phase) in the combiner (proper phase matching assumed).
> 

That is what I thought at first, when installing a few years ago my two antennas, configured that way. But then I 
changed my mind... each preamp sees a signal voltage half of what it would see if the antennas were combined _before_ 
the preamp. So the S/N is worse. The gain you mention is real, but its effect is just that of compensate for that lower 
S/N... so the net gain is zero.

But of course you still gain in making the coax and combiner losses irrelevant, being now placed after the preamps.

73  Alberto  I2PHD