Topband: MFJ 1025

[W2pm at aol.com]

In a message dated 1/8/2007 4:48:50 PM Eastern Standard Time, k6se at 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.