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.

On Wed, 12 Jul 2006 00:42:10 -0500, wrote:

On Tue, 11 Jul 2006 10:00:01 -0500, Bob Bob wrote:



thanks for your reply and those from others
will try some of your suggestions to include a game of fox and hounds G
have to remember, this is an ICOM 736 which is what? 40 yrs old??

Built late '80s, early '90s. Not that old, really.

Bob
k5qwg


it does not have some of the circuitry yours has. But then, it is almost
completely analog, which i like. Turn a know or button and it does something.
= no menus to speak of.

73s
K5DAM
chas

On Wed, 12 Jul 2006 00:42:10 -0500, wrote:

On Tue, 11 Jul 2006 10:00:01 -0500, Bob Bob wrote:

No doubt I will be mentioning stuff you have already tried and tested...
I assume you mean QRN rather than QRM?

Hi Bob
yes, QRN it is ... how foolish of me. sigh


Hi Chas,

Bob² asked for other tests that you either haven't done, or haven't
reported.

You need to examine more than antennas to solve your problem. I had a
noisy TR relay that did the same thing (bad contacts).

A good tech will attempt to partition his station by halves to
discover the source of noise. For you, simply short the input of your
rig. Does the noise go away? If so, your problem is external to the
rig (there's every chance that your problem is here, there's every
chance it isn't). A simple test like this can eliminate a world of
grief.

Bob² suggested killing power around the house. A very good suggestion
that removes local sources from remote sources. It is also a very
simple one too. Running off a battery with the complete house shut
down can tell you what your noise floor is.

Time of year is significant, along with weather conditions. Is this
noise seasonal? I had a bad telephone ground that got worse WITHOUT
rain (I live in rain city, so this was only an occasional problem that
seemed insoluble).

Your report:
there is no real static or tones or motorboating or anything distinctive. It
is just plain, old NOISE!!
is quite odd in that static is classic plain old NOISE!!!!!
You need to be more descriptive because this is not plain at all if it
is distinctly different from static.

If you have a portable SWL radio (or just an AM transistor radio), you
need to walk the neighborhood and see if the noise is generally heard,
or just on your block, or just in your lot. Neighbors with fishtanks
are a leading culprit.

73's
Richard Clark, KB7QHC

On Thu, 13 Jul 2006 22:31:09 -0500, wrote:

On Thu, 13 Jul 2006 17:01:22 GMT, Bob Miller wrote:


Built late '80s, early '90s. Not that old, really.

no kidding, compared to the new Digital rigs, it seems so much older.G
thanks again
chas
K5DAM

Actually, the 736 was introduced in the Spring of '94, so yours is 12
years old, tops.

Yep, they've come a long way...

bob
k5qwg

wrote:

Hi Bob
yes, QRN it is ... how foolish of me. sigh

but, this evening I just tried 4mhz and saw S/N of 9+
and going up to 7mhz, the QRN is even worse.

there is no real static or tones or motorboating or anything distinctive. It
is just plain, old NOISE!! it is so high that I cannot even hear my NCS very
well and he is about 30 mi North of me. Even 75m should allow local
intelligibility and reception regardless of propagation.

Not always. It's quite common to see a skip zone on even 75m.
It's more common in the winter than summer, but can happen any
time of the year. We are in the low end of the solar cycle, so it's
more
common right now. As one already asked, you need to determine if this
is normal atmospheric static, or some type of local line noise.
That you hear it on the higher bands kind of points to some local noise
being a problem. You say 1900? Is this GMT? Sounds like you are
talking in the afternoon...?? Or do you mean 7PM? ??
75m is unstable early in the evening. It's common to see a skip
zone where you don't hear stations close to you. Most of the time,
this clears up about 10-11 PM, but it varies... In the winter, in the
low solar
cycle, it's not unusual to see the MUF drop below 4 mhz between close
stations. But again, this will often raise back up later at night.

A fellow on another site or forum suggested an NVIS as you have.

Absolutely.

I am
considering a 63' wire about 10 ft above and across the yard (which has about
4" of iron ore for a base) so I should get good reflectivity espec with all
this rain. I might attach it to a 15x20' steel patio cover at one end if I
can find a way to insulate the cover from the pipes into the ground. or do
I want it grounded? I am getting so confused and frustrated. I can
certainly remember in the 1950s how low the QRN was except for sunspots, etc.
or someone with a "noisy" auto engine.

Forget the gimmick antennas. They won't help. How good is the antenna
of the net control station? Maybe half the problem is on his end?
Is he running any power? It's July. It's normal to have a high noise
level
at this time of year. S9 noise level is nothing unusual. So this means
you
need to use the most efficient antennas you can, and power won't hurt.
I have no trouble talking in the summer using 100w, but I run coax fed
antennas such as dipoles, etc. Right now I'm running a coax fed
turnstile
on 80m.
You mentioned what antenna you had, but I don't know what that is...
It sounds like one of those "all band compromise" antennas though.
I'd ditch it, and stick up a regular old coax fed dipole. Nothing you
can use
will be any better, or more efficient. Use a 1:1 balun, or a coax
choke at
the feedpoint to ensure you don't pipe shack noise back to your
receiver.
Forget the carolina windom. BTW, most any wire antenna at 35 ft is
going
to function as a NVIS antenna. Most of the radiation is straight up.
What
really counts is the total system efficiency. You don't want to waste
any
power in tuners, intentional resisters, etc... A coax fed dipole, loop,
turnstile,
etc is appx 95+ % efficient as far as the total system efficiency.
Some use full wave loops for NVIS on 75, but there is really little if
any to
gain over a 1/2 wave dipole. If parts of the horizontal loop are close
to the
ground, it's quite possible for the 1/2 wave dipole to outperform it,
if the
dipole is well up in the air. Max current is at the apex of a dipole
or
turnstile. So it's usually well up in the air away from ground. A low
hanging
loop can have high current points fairly close to ground. So I wouldn't
use a
horizontal loop unless all sides were fairly high in the air. Even
then, I doubt
if much advantage. I remember back in the 80's , I compared horizontal
loops,
and dipoles back and forth, and could hardly tell much difference at
all.
I came to the conclusion the extra work for the loop didn't pay off.
:/
I think the turnstile is slightly better than the loop, or the dipole
for 75m NVIS.
It's pretty much my favorite lower band NVIS antenna. The turnstile is
real
good on 40m in the daytime. Your memories of a quiet 75m were probably

in the winter...Wait about 4 months.. It'll get quiet again..
MK