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

[Andre Kesteloot]

-------- Original Message --------
Subject: Re: LF: Big vs small RX antennas
Date: Thu, 19 Dec 2002 01:40:10 +0000
From: Dexter McIntyre W4DEX <dmcintyre at att.net>
Reply-To: rsgb_lf_group at blacksheep.org
To: rsgb_lf_group at blacksheep.org
References: <ba.329865bc.2b327124 at aol.com>



The first 136 kHz US receptions of G3AQC and MØBMU made nearly two years
ago were made with my 160 meter dipole.   The dipole is supported with a
1 meter side arm from the 95 foot level of a 100 foot, insulated guy
wire tower.  The home brew open wire feed line was fed as a single wire
with a series pot core inductor to bring the antenna to resonance.
Later test were made comparing the TA signals received with this antenna
to a 3.3 square resonant loop.  This loop was matched with a single turn
pick up loop.  The two antennas were comparable for 136 kHz reception
most of the time.

Last year I constructed a new receive loop, octagon in shape, twenty
turns, a little over 3.3 meters diameter.  This loop is center tapped
and feeds a balanced preamp.  Every comparison I made showed this
balanced fed loop to outperform either the old loop or the T vertical
wire.  I'm a firm believer in the balanced loop design.

W4DEX
www.w4dex.com

MarkusVester at aol.com wrote:

 > 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
 >