[Lf] [Fwd: LF: Big vs small RX antennas]

[Andre Kesteloot]

-------- Original Message --------
Subject: LF: Big vs small RX antennas
Date: Wed, 18 Dec 2002 19:47:32 EST
From: MarkusVester at aol.com
Reply-To: rsgb_lf_group at blacksheep.org
To: rsgb_lf_group at blacksheep.org



Hi John and LF group,

 > Just curious -- since the signal to noise ratio in my receiving
 > installation
 > appears to be limited by external (man-made and atmospheric) noise, 
rather
 > than noise in my preamp/receiver, how would a 100 foot tower improve that
 > situation?
 >
 > John Andrews, W1TAG



A big vertical does help a lot against local noise-sources (neighbours'
TVs and SMPSs), but with anything originating further away than a couple
of 100m, it makes absolutely no difference.

However the directivity provided by a magnetic receive loop can be
valuable. If all of the noise was coming in isotropically from the
horizon, the figure-eight pattern would theoretically have 3dB better
SNR than a vertical, and a cardioid combination would gain 4.8dB. In
practice, of course one can often null out a source of QRM or a
thunderstorm front and have far greater improvement.

The only problem I am having with small loops is that they seem to be
much more prone to local pickup than the E-field antenna - at least in
my suburban area which has underground mains wiring. The 86cm-diameter
pair in the garden is often swamped by notorious 100Hz-modulated
carriers which at the same time I can hardly see on the marconi.

73 de
Markus, DF6NM