In a message dated 1/8/2007 4:48:50 PM Eastern Standard Time, k6se@juno.com
writes:
The MFJ noise cancellers require the the signals from both antennas are
equal level. That means that with the 1025 that the "noise" antenna
needs a preamp because it is usually a smaller, non-resonant antenna.
There are "gain" controls on both antenna inputs that allow you to
precisely adjust it so that the signals are equal on both inputs.
The 1026 has a built-in preamp for the "noise" antenna input that *is*
able to be used with the built-in whip antenna *or* an extenal
"auxiliary" antenna.
I recommend the 1026. The extra $10 or so that it costs is insignificant
and well worth it for the built-in preamp.
W2PM reply:
I have never been able to find a null when the 2 signals (noise and main)
are "equal". In fact it always seemed that the noise had to be at least 3 db
less than the main signal using the receivers S meter. I know this fly's
against the manual guidance and the nulling theory, but this is what I, and
other
have found here using either the MFJ unit or the ANC4. I also have to
drastically reduce the main antenna gain when using the big TX antenna which
really sucks in the noise - beyond S9 at times.
Also, the "noise antenna gain"control is really more of an attenuator than a
gain control per-se. It does not affect preamp gain but rather the total
noise signal level entering the mixer. The preamp gain is jumper selected.
This
is an important difference between the internal preamp and using an outboard
one where you have control over the noise level going into the unit in the
1st place. As most of us know, noise nulling is not an exact science but in
practice somewhat of an art and I've found the more controls the better -
unless you have a perfect environment with one specific noise source at a
steady
amplitude and phase level. Many MFJ nuller or ANC 4 users report lots of
frustrations. Here, on ideal nights I can nearly null out offending noise
completely with the 1025 and a selection of noise antennas AND directional rx
antennas. I seldom use the nuller with the big TX antenna but that does work.
With a FLag and Pennant as the "main" antenna and the MFJ nuller with a sense
antenna, and using the TX antenna only for TX (this requires a bit of rat's
nest wiring or switching) there are many times I can bring down the noise
floor to under S1 when without these resources it is well over S7 - 9, or
worse
if using the TX antenna.
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