There is a simple mod for the MFJ-1025/1026 that improves the low frequency
performance. See
http://www.hard-core-dx.com/nordicdx/antenna/special/mfj1026_6.html
73,
Barry N1EU
>From: "Tod Olson - Idaho" <tod@k0to.us>
>To: <topband@contesting.com>
>Subject: Topband: 4. MFJ noise canceller (Donald Chester)
To: <topband@contesting.com>
>Date: 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
>
>_
>
>_______________________________________________
>Topband mailing list
>Topband@contesting.com
>http://lists.contesting.com/mailman/listinfo/topband
_________________________________________________________________
The new MSN 8: smart spam protection and 2 months FREE*
http://join.msn.com/?page=features/junkmail
|