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
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