The phase coherence of the signal versus the noise has nothing to do with
it.
Both are signals. If they are both coming from the same direction, then the
increased antenna gain won't improve receiver SNR. If on the other hand
the noise is coming from a different direction, or if it is a composite
coming
from many directions, and the 3dB increase in gain is acheived by an
associated 3dB increase in antenna directivity (as opposed to efficiency
improvements) in the direction of the signal and not the noise, then
receiver
SNR will improve.
Since noise is sometimes a composite with nearly equal contributions coming
from all directions, and at other times dominated by specific sources, it is
hard to generalize as to the specific improvement in SNR that will accompany
an improvement in RX antenna directivity.
73 de Mike, W4EF........................
----- Original Message -----
From: "R_Davis" <WD8JJA@arrl.net>
To: <amps@contesting.com>
Sent: Friday, March 08, 2002 9:14 AM
Subject: Re: [Amps] al-1200 question
> NOT TRUE!
> The received signal is a coherent source, while ambient noise is
incoherent
> (random in phase), so you will definitely se an increase in signal to
noise
> ratio. This is unlike adding a preamplifier which WILL amplify the noise
> and signal coming into the antenna.
>
> ----- Original Message -----
> From: "Pete Smith" <n4zr@contesting.com>
> To: <amps@contesting.com>
> Sent: Friday, March 08, 2002 7:37 AM
> Subject: Re: [Amps] al-1200 question
>
>
> At 07:14 AM 3/8/02 -0500, wd8jja wrote:
> >Here is something to ponder. Doubling your transmit power nets you 3 dB
> >gain on transmit. Improving your antenna by 3 dB, whether by improving
the
> >gain or reducing loss, nets you 3 dB on transmit AND RECEIVE !
> >
>
> Well, yes, but in most cases at HF the added receiving gain is not really
> useful, because your ability to hear is limited by signal-to-noise ratio,
> not path loss, and the extra gain will just bring up the ambient noise by
> the same amount as the desired signal.
>
> 73, Pete N4ZR
>
> Check out the World HF
> Contest Station Database at
> www.pvrc.org
>
>
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
|