Topband: Noise Cancellation Options?

[Herb Schoenbohm]

Walter Miller, AJ6T wrote:
> My new 160m sloping "T" transmit antenna seems to be working well, and 
> now I need to attack the local RX noise problem (again).  A small 
> shielded loop and K9AY help somewhat, but reception is still overwhelmed 
> by noise at my QTH.  I have tried both the MFJ-1025 and MFJ-1026 noise 
> cancellers with an external noise pickup antenna but I have not been 
> able to achieve a null, even with equal S-meter readings from the main 
> and noise antennas.  
Walt,
Noise reduction from multiple directions and sources is not going to be 
easy.

 I use several MFJ-1026 units, both for noise cancellation purposes and 
for phasing staggered Beverages.  The settings are critical and the 
noise sense antenna and RX antenna levels must be of the same amplitude 
to get nulling.

I was disappointed at first until I did some test runs with some 
distant  BC stations and could make them vanish with proper settings and 
antennas.  I would think that if you are trying to null out noise you 
first need to determine the source and direction. Many locations 
unfortunately have noise coming from different sources and different 
directions so nulling out noise with the 1026 is going to be impossible.

My suggestion is to start by using receiving antennas like Beverages, 
even short ones, to get some directivity away from the noise if possible 
and thus cut down the level of the worst offending noise.  Then with the 
MFJ unit using a reduced noise antenna Beverage or Loop on the main 
connector add the noise pick up antenna to the other input.  Set the 
levels so they are equal.  Then proceed to the phasing control to 
achieve a reduction in noise.  If you have multiple noise sources of 
different amplitudes and directions you are not going to be a happy 
camper with any of these units, or if you RX antenna is a vertical or 
close to the noise source, the same problems will exist. 

To verify the unit is working try two distinctive different antennas on 
a BC station, in this case even the desk top loops will work for such a 
test...the small wire muti-turn loops that are packaged with most AM/FM 
tuners.

73

Herb Schoenbohm, KV4FZ