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" <[email protected]> To: "Dave Cuthbert" <[email protected]>, [email protected] Cc: "Topband" <[email protected]> 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 _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
