Hi Rick,
A noise receiving antenna close to a noise source is used in conjunction
with a higher performance receiving antenna such as a Beverage or an
array of short verticals and a passive or active noise canceller.
A small loop antenna provides a mechanically steerable null off of both
sides of the loop. Null beamwidth is just a few degrees at the 3 dB
points, otherwise a small loop is an omni-directional receiving antenna.
Simply turn the loop to minimize the interfering noise signal strength.
The smaller the loop, the deeper the null depth but the smaller the signal
strength of desired signals. A small loop antenna requires a low noise
high gain pre-amp directly at its feed point for optimum sensitivity.
A small loop antenna should be close to ground for optimum null depth.
Horizontally polarized skywave signals penetrate the nulls if a small
160 meter loop antenna is much higher than than about ten feet above the ground
On 160 meters a small loop antenna provides:
- a 30 dB null off each side of a 5 foot diameter loop.
- a 25 dB null off each side of a 10 foot diameter loop, or
- a 20 dB null off each side of a 17 foot diameter loop
73
Frank
W3LPL
----- Original Message -----
From: "Richard (Rick) Karlquist" <richard@karlquist.com>
To: "Dave Cuthbert" <telegrapher9@gmail.com>, n2ic@arrl.net
Cc: "Topband" <topband@contesting.com>
Sent: Saturday, March 14, 2020 10:17:59 PM
Subject: Re: Topband: Slightly OT - amplifier noise
I am trying to understand what these noise cancelling
schemes do that couldn't be done with a simple loop
(rotating the loop until the noise drops into one of
the null directions). You can easily prove to yourself
with a hand held AM BCB receiver equipped with a ferrite
bar antenna that even the worst power line noise can
almost always be greatly suppressed by properly rotating
the receiver. Similarly, I have had good luck with
small tuned loops (10 feet perimeter) nulling power
line noise. Smaller loops seem to have deeper nulls.
It is critical to keep loops away from your other antennas
and power wiring. Otherwise, they will not exhibit a
good null.
Rick N6RK
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