[Elecraft] Diversity receive versus QRM eliminators

[hb9cvq at hispeed.ch]

Hi All,

I use in my K3S the RX in and RX out (RCA plugs) on the backside for
inserting the denoised signal  from my DXE NCC-1 Phasing Box output plug.
This box has two channels, were one can do e.g. up to -180deg phase
reversal. CH A and B signals are finally send to an internal power combiner
and to K3S RX in.

My have 2 selectable TX/RX antennas, 2x36m tuned doublet 160 to 6m @ 24m
center and a Steppir DB18E @ 18m.
RX signal come out safely from K3S RX (out) going to CH A NCC-1.
My QRM local noise pick-up ant is a 1m diameter ALA 1530 electronic mag.
loop (predominantly picking up local noise, no DX , horizontally mounted in
the attics, about -60dB decoupled from TX antennas)  
This signal goes into CH B of NCC-1
By carefully equalizing/adjusting the amplitudes CH1 /CH2 NCC-1 I then try
do "Anti Phase". This will mostly reduce the local noise on the used main
antenna.

The limitation is you can only effectively  focus (phase) on one single
local QRM source. The unit NCC-1 is good up to around 17m Band. It is hard
to get more than 20dB S/N (about 2.5 S-Units) improvement.

In some local noise cases, not being a point source (Line source : PLC ,
VDSL etc. ) I am more successful using a LISN ( EMC , Line/Mains 50 Ohm
stabilization, decoupling network, 230V, 50 Hz) to safely replace the signal
from the mag. loop.
This procedure picks up the conducted noise on the mains in the house/flat
more in an integral way. This does not act as a "point source"

Experiments with predominantly E-field ( small/short dipole antennas) for
local noise pick up are ongoing.

73  Andy
HB9CVQ, DK2VQ, AK4IG
https://www.qrz.com/db/HB9CVQ


-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
Behalf Of donovanf at starpower.net
Sent: Montag, 29. Juni 2020 19:51
To: Elecraft Reflector <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] Diversity receive versus QRM eliminators

Diversity is not helpful as a QRM eliminator. 


Antennas with steerable nulls can be helpful, small loop antennas have very
deep nulls but also require a high gain, low noise figure preamp and very
careful attention to common mode rejection during installation 


73
Frank
W3LPL 

----- Original Message -----

From: gt-i at gmx.net
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Monday, June 29, 2020 5:18:30 PM
Subject: [Elecraft] Diversity receive versus QRM eliminators 

Hello all,
In a recent rush to eliminate urban noise I bought an QRM eliminator. 
The working principle is to null out signals by shifting the phases of two
antennas (one main/tx and one rx). I can see the effect sometimes, but it is
not the holy grail for all types of QRM. I still don't get rid of the
PSU/LED/plasmaish noise here, sometimes the S/N is a bit better but maybe
thats my inner impression to justify buying this thing. 
Now, I do wonder how this differs from diversity receive, effectively versus
local QRM. 
Note I have a 10m vertical as the 2nd ant, while the main ant is horizontal.

Any thoughts or hints ? 
tnx 73 Gernot DF5RF 


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