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Bob · November 10th 06, 06:12 PM posted to rec.radio.shortwave

wrote:

Don't forget to look at John Bryant's pdf showing another way to build
a
an effective common mode choke for receiving applications. Bryant's
torroid will over heat with as little as 10W on Tx!
__________________________________________________ ________________________
That's what I meant by Devoldere/Bryant, but I wasn't clear enough...
Devoldere's book (ARRL Low Band DXing) is where Bryant & Nelson got the
info from originally.
__________________________________________________ ________________________

http://www.dxing.info/equipment/coax_leadin_bryant.pdf

I have found that the most effective way to reduce your QTH noise level
is:
Step 1: Use a portable SW receiver, I use a DX398, with a simple loop
to check every circuit, and every device in your home and outbuildings.
Be certain to check everything. Doorbell, Smoke alarm, water heater,
PIR lights, coldcathode florescents lamps, telephone devices, TVs, VCRs
DVD/CD players, audio cassette decks(I had a pioneer that had a nasty
spur on ~5.1 @ S9), battery chargers, well you get the idea. Check
every
thing. A lot of the RF noise, in every case I have worked with, comes
from
within or very close to your home.
Step2:After finding and logging the noise, start fighting it. The
Curtis RFI
filters I mentioned are easily made into "things" to go between the AC
mains
and the device. They use PC style IEC power cord for inputs, so it will
be
useful to gather at least one per filter. For those devices with it
will take two
cords per filter, one for the AC in and another that you simply cut the
male
end off and solder to the filter's outputs. Other devices will need the
IEC input
cord and either have the device hard wired to the filter output, or the
use of a
suitable female connector.

I found it helpful to add a 0.1uF 1KV disk cap across the filter's
output. I
used liquid tape to unsulate the filters hot end, and in most cases I
used
large diameter heatshrink to protect the whole filter assembly. Regular
electrical tape would work, and the really industrious can build the
filters
into mini-boxes. For our HiFi/"Home Theatre" center I built my own
fitlered
power "strip" with 10 RFI filters in one metal box with 1 heavy AC
input
cord that I fan out to each filter input. I use some 1" square females
because
I had a chasies punch. I got fancy and added some relays to allow the
power
to be remoted. Most modern devices don'e have real power switches as
something
is always left alive, so by really turning everything off I reduce the
off state noise
and as important, reduce the chances of AC line spikes damaging
something.

For Wall Wart, I try to pick RF quite units to begin with, then add
ferrite on the
output, and in extreme cases I crack the case open and bypass the
diodes
with 1000pF/0.0001uF caps. As Telemon pointed out, it would be more
effective
to design and build a snubber for that specific circuit, but I have
found the 1000pF
to almost always work very well.

Be sure to check the phone line at the NID/demarcation box. A friend
had
nasty RFI coming down the phone line. With more DLS being added all the
time, I check mine once a week or anytime I hear a new constant RFI
source.
Ferrite will keep it out of your home.

Use a real RF ground and do not rely on the house hold electrical
ground.
Use good quality coax.
If you are using a "wire" antenna, be certain a matching transformer.
If you are using a non-dipole acitve antenna you will almost certainly
have
to use a lot more ferrite then you first would think. Active dipoles
are
much more imune, but still need some common mode filtering.

!!ALL of the active non-dipoles that I have played with require a very
good
ground at the base of the antenna.!! Good means at least a 4' ground
rod into moist soil. 8' is better, but awkward to move. I plan on using
a 4' until I find the quitest spot then switch to an 8' rod.

Sorry for the length of this, but I thought you mind find it useful.

Terry

Not too long for the info given! I am working on these exact things
courtesy of information passed to me by your friend Will. You didn't
know you were helping somebody in Syracuse, NY, but you have been.
Will has been kind enough to send me a lot of details on how you showed
him your "noise audit" procedure and ways to kill the noise. I just
received 20 of the Curtis filters from Hosfelt.
You helped Will and a bunch has "trickeled down" to me. Thank you very
much.

Bob