RadioBanter - View Single Post - Need help on QRM rejection ( WITHOUT A BEAM !!)

[email protected] · July 15th 06, 12:10 PM posted to rec.radio.amateur.antenna

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