[1000mp] 1000MP Noise and the MFJ-1260-65

[Mark Shaum]

----- Original Message -----
From: "Ronald Walters" <rwalters8@cfl.rr.com>


> This is message is not directly related to this reflector but I hope
that
> someone can provide feedback.
>
>
> Question - I am thinking about trying the MFJ-1265 Noise phasing unit.
Have
> read an old review on ARRL and other comments on some bulletin boards
but am
> wondering if anyone out there has experience with the unit and what
their
> honest impression is.

Ron,

I have a similar situation here with intermittant noise radiated from
lines in and out of a nearby (100 yards) small substation.  The noise,
when present, varies in composition.  Sometimes the built in blanker on
the MP can take it out, sometimes not.  When it doesn't, I use a JPS
ANC-4 and with a somewhat varied selection of noise antennas from a 10
foot wire to my 170 foot 160m sloping-L. I can usually null noise 40 to
60 db on 160 to 20 meters. I don't need it frequently on higher
frequencies, but it does its job.  There is overall 5-10 db reduction in
desired signal strength (usually) with the noise canceller in line.
It's a bit touchy to adjust for null, and re-nulling is necessary for
wide frequency hops within a band.  Larger knobs help.

I also have the MFJ unit.  While it will attenuate the noise equally
well in most cases relative to desired signal, its internal rf amps
raise the noise floor of the overall receiving system high enough to
mask weak signals that the MP could well have received otherwise.  Not
very noticible on 160 and 80, but increasingly notable on higher
frequencies.  My unit is an older one, MFJ may have addressed this in
the meantime.

Choice of a noise antenna is important with these out-of-phase nulling
devices in the receive path.  The closer you can get the noise strength
to that which exists on your main receiving antenna, the better luck
they have in delivering a deep null.  Once we thaw a bit here I plan to
mount a (roughly) 25 foot noise dipole at about gutter level on the
front of the house, parallel to the power lines.

If you use a noise antenna with a reasonably large capture area, be sure
to figure out some way to protect the noise inputs of the noise
cancelling devices from your own xmit RF, especially if you run high
power.

Using the rx ant in and ant out jacks on the rear of the MP makes
hooking these things up easy.  Just tap the "RX" antenna button on the
transceiver and the noise canceller is toggled in-line.

73! - Mark
------------------------------------------------------------
Mark Shaum K9TR
email: k9tr@dtnspeed.net
http://www.qsl.net/k9tr
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