Topband: 4. MFJ noise canceller (Donald Chester)

Tod Olson - Idaho tod@k0to.us
Thu, 5 Dec 2002 00:24:29 -0700


I purchased the MFJ Noise canceller about 5 years ago at Dayton. I have been
using recently to combat 80 meter noise. It is highly dependent upon the
sense antenna. For best noise canceling the sense antenna should provide
sufficient noise signal to 'phase out' the noise on the main antenna. I find
that it is preferable to have sufficient signal so that I do not need to use
the built in sense antenna signal amplifier. For my 80 meter noise I used an
80 dipole as the sense antenna and my HyTower for transmitting. They are too
close together, however, and the energy pickup when transmitting was
sufficient to burn out the small bulb used as a fuse in the external sense
antenna circuit. I replaced the bulb (several times) and finally have
decided to add a small relay and ground the sense antenna input when
transmitting.  You may wish to consider this.

On 80 meters the signal loss is not significant but on 160 there is a
substantial signal loss (in my unit at least) even when the output is set to
maximum. I suspect that the circuit is optimized for frequencies above 160
meters. I plan to measure this loss and see what might be done to restore
the signal. Also, because the signal from the main antenna is processed to
some degree even when the sense antenna input is set for minimum gain, there
probably will always be some signal attenuation.

One other point, even modest frequency excursions (+/- 15 kHz) will require
adjustment to the phase and level controls if you wish to reduce the noise.
In some cases you will not be able to reduce the noise because it comes from
multiple sources and you can only phase out one at a time. Still, it does
help improve the signal to noise ratio in some cases and may make the
difference between hearing a station and not hearing them.

Tod, KØTO

_