[Elecraft] Using MFJ-1026 Noise Canceller on 6m-eme

[chetsubaccount at snet.net]

Hi Ed,

Wow, looks like a clever scheme.
 I was not aware the K3 subrx had an IF output. Did you have to tap into
that part of its circuit?

73 and GL,
Chet, N8RA

-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
Behalf Of Ed Cole
Sent: Friday, April 15, 2022 9:32 PM
To: MagicEME at groups.io
Cc: elecraft at mailman.qth.net
Subject: [Elecraft] Using MFJ-1026 Noise Canceller on 6m-eme

Diagram of final configuration: http://www.kl7uw.com/6M_NOISE_CANCEL.jpg

This a basic phasing unit to reduce band noise on HF bands.  But first I
tried it on 6m where no null was achieved.

Next I configured to use the 1st IF output of my dual-Rx Elecraft K3 running
in Diversity mode which phase-locks both Rx to the main VFO.

That involved using an outboard SDR to detect the 8.215 MHz IF signal and
supply audio to my computer.  Sensitivity was too low on the second Rx so
required opening/inspecting cables inside the radio.  I found the synth coax
not seated well to the second Rx.  Re-seating the connector fixed that.


But I still had too low an audio level from the 8-MHz SDR to drive wsjt-x.
A bit of research found the proper dialog box to adjust mic gain.
Apparently the K3 line output is much higher than the SDR audio (LP-Pan2).

Original design involved using an external preamp for the 6m noise antenna
(3-element yagi) but I found I had adequate gain using the MFJ internal
preamp set to gain=2 (out of 10).

To add additional RF protection to the MFJ, I added a coax relay to
disconnect the aux input of the MFJ.  It does have a TR control line to give
protection to the main Rx line, but none to the aux Rx input.  My main Rx is
fed by a preamp at the tower located behind a TR relay.

I adjusted audio levels for main and aux inputs so wsjt-x read 36 on the
audio bar meter for each.  With both inputs it read 40.

Placing the K3 into diversity mode I could null about 6-dB (reading dropped
to 32/34.

No idea if this is enough noise reduction for 6m where I regularly see
S5 pointing NE toward MR,  Pointing SE local noise often drops to S2/S3. 
  One s-unit is 6-dB.

Next is to test with actual eme signals.

73, Ed - KL7UW
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