Hi Chas

No doubt I will be mentioning stuff you have already tried and tested...

I assume you mean QRN rather than QRM?

- It is probably worthwhile seeking out the source of the noise. Such
things as turning house equipment off and listening etc. I have
horrendous QRN here (Longview East Texas) from power line noise. It is
worse of course on HF but it does interfere with weak signal work on 2m.
The noise dissappears during and about an hour after rain... I have
already done a walkaround with the 2m SSB RX to determine where the
source is (pole hardware near a oil pump about 200 yards away) but
havent contacted the power company yet. (Keep in mind that by law they
are obliged to fix it. The FCC apparently helps a lot here. Your MARS
status will probably make a big difference as well)

- Most radios are very good at reducing pulse noise like from a car
ignition. My oldish Kenwood radio also does a credible job on the PLI at
the expense of some selectivity. It may be worthwhile having a play with
the noise blanker circuit to also suppress noise with a slower rise time
(like PLI). You may also want to try using a separate sense antenna and
amplifier into the NB circuit. If your blanker isnt affecting the noise
you may need to increase its sensitivity. (make it adjustable though!)

- If you are message handling only, a digital mode (like Olivia, PSK
etc) will go a long way to getting the signal through. Useless of course
if you are phone/radio patching families..

- Yes I agree, try another RX to see if the S/N is any better. If it is
then the first radio might have some problems.

- Elsewhere on this group you will have seen a discussion on noise
reduction techniques using antennas. I wont repeat it here. I am sure
you know the vertical is "noisiest" and a pure horizontal dipole is
"quietest". Perhaps the inverted V construction is responding to the
local noise more than a straight horizontal antenna. Using a separate
low antenna (often a magloop) for RX can also yield much better S/N than
using a highly placed one. Since noise level generally on HF is much
higher than the RX sensitivity this can work very well. It isnt a viable
solution (say) from 10M and up through VHF/UHF

- External DSP might be viable. You can get software nowadays that will
take the radio's audio output and "wash it". It is much better to use
the IF for DSP but PC soundcards can only sample at 44kHz or so. I
havent dabbled in this much but for Windows have a look at
http://www.qsl.net/dl4yhf/spectra1.html and see if it helps. Of course
your PC power supply etc may then cause a problem!

- If you have one noise source that looks like a point source radiator
(ie not power lines) phase cancellation techniques might work. ie using
a second antenna and a passive phase delay circuit tune for max s/n by
adding the noise to itself 180 degrees out of phase.

- Your feed system might be responding to signal. I dont know the
antenna design you mentioned but unbalanced "balanced feeder" tends to
radiate as well as receive and since it is vertical will respond to
noise. A balun is the supposed trick here but I am sure others will jump
on this often contentious topic.

Like I first mentioned try to find the location of the noise source. If
it is some power lines or a known location put up your windom such that
a nul is pointing in the noise source direction or at least not parallel
to power lines.

Hope this helps

Cheers Bob W5/VK2YQA East Texas

wrote:

I am working with MARS on 75m. I am seeing some horrific QRM esp today but
generally every day and definitely need some help on rejecting the noise.