In a message dated 1/26/2006 8:49:09 AM Eastern Standard Time,
richroad@telusplanet.net writes:
I have had some success using this device for cancelling noise, but often
run into a problem where I run out of phase adjustment. If I change the noise
antenna, I don't get enough noise signal. On W8JI's website he talks about a
mod to add a capacitor from the bottom of R16 to ground. Has anyone tried
this, and if so: Did it work, and what size of capacitor did you use? Tom says
it
is so long since he looked at the 1026 he can't remember the details.
I know two people who did the mods and they resulted in significant
improvements. I have been able to make some repeatable observations of
MFJ1025/26
usage and note the following which may be helpful to some with issues with
this
box.
NOISE LEVEL:
IF your local crud noise is very strong from the main antenna - S9 plus
category (as is nearly the case all the time in suburbia) - your noise
antenna
MUST product at least S7 level but usually higher. It depends on the noise
but in the cases Ive been able to repeat I have a Inv L 30 feet parallel to a
24KV powerline 200 ft out back! So you can imagine the crud (many times the
line is quiet believe it or not < S3 noise). Typically the noise antenna may
not give you that signal level and the MFJ unit without Tom's mod's has
considerable noise antenna attenuation. In my case I use a tunable preamp for
the
noise antennas (MFJ959C) and crank the noise level to S9.
The noise level can be quite critical too else you will only get a null with
very VERY low main antenna level settings on the MFJ and the phase adjust
ment will be super critical. It will result in dramatic, near perfect null, but
the resultant S/N is unusable due to low main signal.
You will have to play with actual noise levels but when these very loud
local crud conditions are present, I find the optimum setting still results in
the MFJ unit not being able to set the main antenna level beyond the 10 o'clock
position of the knob - which is less than half total level. Nonetheless the
results are nearly always quite usable and the null near perfect.
When noise levels are under S6 or so (on my FT1000 and TS850) the nulling
action usually doesn't require preamplification of the noise.
OTHER NOTES:
IF you manually reverse the main input with the aux input (DONT
TRANSMIT!!!!) you can see the effect of one of the mods on 8JI's site. It works
very well
on Topband but is unnecessary on higher bands.
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