[Amps] al-1200 question

Vic Rosenthal rakefet@rakefet.com
Fri, 08 Mar 2002 10:09:15 -0800


Steve Thompson wrote:

> Vic said:
> >Since the desired signal comes from one direction and noise is more or less
> >evenly distributed, a directive antenna does improve the signal/noise
> >ratio.

> I can see this is the case where you have noise sources with a specific
> location, but I have a feeling it doesn't apply to general atmospheric noise
> that's uniformly distributed.

That's exactly the case in which it I think it DOES apply.  The signal comes
from one point, but the noise comes from all over.  So as you narrow the beam
width you reduce the sum total of noise that is picked up.  Then you multiply
this lesser amount of noise by the gain of the beam.

I would guess that if you had a non-directional antenna with the same capture
area as a beam, at the same location, with both antennas perfectly matched,
etc., then the general atmospheric noise that you would hear would sound exactly
the same on both antennas!  The difference would be that the noise on the beam
would be reduced because of coming from a smaller area, and then multiplied by
the gain of the beam.  The signal would be multiplied by the gain of the beam
but wouldn't have been reduced.

Does this reasoning make sense?

73,
Vic, K2VCO
Fresno CA