Topband: Slightly OT - amplifier noise

[Ken Claerbout]

A couple of issues I see.  It depends which direction(s) the noise and
desired signal are coming from.  You may null the noise and signal.
Also, the loop is bi-directional.

I've been playing with a DX Engineering RF-PRO-1B at ET3AA and it
works.  Thanks to Tim and the gang for their support.  But there is a
lot of noise and not being able to null everything except the desired
direction I suspect is an issue.

Our noise is close in, so I have some upgrades in place using a Hi-Z 4
square and NCC-2 with a "noise" antenna as Frank mentions.
Unfortunately the next thing I need to do after I send this, is to
cancel my reservation for the 27th of this month.  Africa looks like a
pretty safe place Covid-19 wise at the moment.  But one look at the
long lines at immigration did me in.  I don't have the patience for
that.

73
Ken K4ZW


On Sat, Mar 14, 2020 at 11:43 PM <donovanf at starpower.net> wrote:
>
>
> 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 at karlquist.com>
> To: "Dave Cuthbert" <telegrapher9 at gmail.com>, n2ic at arrl.net
> Cc: "Topband" <topband at 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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