[Antennas] getting rid of strong QRM ( reception)

2002年9月15日 11:40:01 -0700

Hi Zacharias,
I'm assuming from your description that this is more complex than a bum
power line or someone's noisy vacuum cleaner motor. I have no idea if my
experiences in Oregon, USA might be of help, but here's some things that
have recently "turned on" various complex forms of local QRM (it may not
actually be a motor):
1) Super efficient CPU controlled "instant hot" furnaces in some new
homes...these have both a CPU totally unshielded and unfiltered (likely
non-compliant with FCC regs) and ratty, high current switching power
supplies...most idle with 50KHz wide QRM centered about every 100KHz...when
the furnace with fans, etc kicks on, all hell breaks loose. I've fixed the
closest two with screening and grounding...huge difference...this, of
course, requires access be granted, etc etc.
2) Nearby neighbor runs a small plant nursery with 10-base-T network among
various outbuilding sales registers...every transaction puts out a wideband
burst of crud. Solution was to use some tinned braid I had from an ebay
source and shield the offending cables...several of the CAT5 unshielded
cables were 100 feet long and strung about 12 feet in the air. I had to
build a sample from one of my own and demo it to the owner...then he was ok
with the shielding idea...
3) Some neighbors with nearby PC's cause a variety of problems...usually
has to do with poor cabling, ground-lifting, or older, unregulated
accessories.
So far, I have had little luck getting a genuine all-around solution via
manipulating the antenna type or orientation, although there has been spotty
success.
I hope there may at least be a useful idea in here...of course if it is a
motor AND you can find it, AND the owner will let you near it, the ARRL and
RSGB both have very useful guides on the subject.
regards
John Collins
_________________________________________
----- Original Message -----
From: "Zacharias Liangas" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Sunday, September 15, 2002 03:19 AM
Subject: [Antennas] getting rid of strong QRM ( reception)
> Dear frinds
>> During the recent period an unknown local QRM has been
established/appeared in my area
> that produces a very high QRM level of S9+ 10 across all the SW bands in
my 16m single
> wire antenna ( a height of 5 m ) .
> My system is a reception only rig.
> This noise seems to be a motor type, as using my receiver's (R75') Noise
Blanker partially
> cancels this noise
> I made another temporary antenna, a dipole of 2 x 13 m which unfortunately
is on very low
> heights (only 2.5 m!) with cascaded wires of #14 for the first 6 m then
0.1 mm for the
> remain, with the one side over trees and the other standing over two TV
cables .
>> QRM is still passed through this antenna, although in several bands the
level is lower ( e.g.
> 9 MHz) over a lower gain antenna regarding to the 16m wire . It is also
nice that I use a MFJ
> 1025 noise canceller with the dipole as main antenna and the 16m wire as
secondary.
>> MY problem is that using MFJ 1025 is very critical as changing to several
kHz all sets
> change. And noise is not always 100 % cancelled
>> Does nay other have a better idea for canceling this noise with antenna
only configuration
> or even if there is something I can put in side of the motor? ( in case I
find its owner)
>>> ___________________________________________
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> PP: R75/HF150/MVT7100/D2935 + 16m/1x1 + MFJ16010/1040/1025/752c/462
> http://www.geocities.com/zliangas/
> /trip2k.htm (dlm Bkk,SNG,BAli) /MP3_comp.htm comparison Xing/Fastenc
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