RFI, PART 3
Finding RFI.sources.

This will be a multiple step process. As you find and quieten one
device, you will find weaker
sources. Eventually you will reach a break even point where further
effort isn't justified because
your home is now as quiet or quieter then the RF world.

My basic RF setup uses a DX398 portable LW/MW/SW receiver operating on
batteries. I use a
RFI "sniffing" loop made from a scavenged pill bottle. I wound about
27 turns of ?22AWG solid
wire on a 1 3/8" [labeled 55C PM-10] pill bottle. It measures 19.1uH.
I also made a 3 turn loop
on the same sized bottle and a 100uH radial inductor in a dried out
Sharpie marker case. Because
I am picky, I added BNC female connectors to each probe so I could use
them with other equipment
then my DX398. I suggest that most people only need the first sniffer
and to use a good quality,
RG174, coax [and not to use spiral shielded audio cable!!] terminated
in the proper male connector
for their receiver. In the DX398, by shorting out what would be the
ring or right connector on a stereo
3.5mm male connector, the internal loop MW antenna is disconnected and
the external antenna
becomes active.

The first pass will find noise that is broadband and fairly strong.
Later passes will find weaker broadband
signals and hunt signals from the various oscillator/clocks within
logic devices in your home.

Step one:
Make a list of every electric device in your home. Include telephones,
telephone NIDs, Cable TV
cables, fire alarms, door bells, water heaters, outside lights,
security lights, PIR (passive infrared
lights). Even list all the night-lights. Don't forget your HVAC
thermostats. Be certain to include every
device, because the oddest things will have logic controls. A friend's
new Washing Machine is RFI
Hell!

Step two:
Make a rough sketch or diagram of your home showing every outlet,
light switch and fixture and
EVERYTHNIG that is connected to the AC mains, telephone line, or Cable TV coax. Note
every GFI outlet or breaker and the new Arc detection breakers.

Step three:
Start at every conductor entry point into your home.
Check the telephone NID, and AC KWH meter.
RECC went to smart Focus KWH meters and the first one they installed
was a RFI nightmare.
Since I am a ham, I asked the chief engineer if he would like me to
test his fancy new meter with
1KW of up close and personal RF. I read him the part 15 notice in the
service manual I had located
on the web about "not causing and must accept any RF problems".

I am glad to say he saw the light of reason and came up with a much
quieter unit. They added a meter
base surge protector with minimal RF filtering for free.

Step three:
Start at the breaker/fuse panel/box and pass your sniffer coil over
the panel. I start my search at 4MHz
because based on several years of RFI hunting, most troublesome
broadband RFI has a significant amount
of energy at 4MHz. There is nothing special or even scientific about
that frequency.

Note any noisy breakers. If they are GFI or Arc Detection breakers
turn them off to see if the noise
stops. Some brands are pure noise sources. Gently wiggle each breaker.
Some breakers don't make
positive contact and are noisy.

If you have a noisy breaker, either standard or GFI or ARC, (or
combined GFI and ARC) then you will
need to consider the possibility of changing them or having them
changed. This is not a task for the
uniformed. 120V or 240V will KILL you very fast if you are unlucky
enough to make a conductive path!
Changing breakers is fairly simple and I suggest going to the library
and checking out a book on basic
home repair and reading up on how to do it. Before changing a breaker,
or noisy outlet or light switch,
ask yourself if you have the skills to safely do the work. If you
don't either hire an electrician, take a
course at a home repair store or live with the noise!

Step four:
The fun part. Go to every device, every outlet, every light switch and
every light fixture and note any RF
noise. The DX398 is a good all around choice because of its small
size, wide frequency coverage S-meter,
and RF gain control.

Test everything in both the on and off states. A friend's Plasma
Screen TV was worse when it was
off then when it was on.

Some devices are noisy but aren't a problem. We have some Sylvania
Compact Florescent Lights
that are RF hell within 12" or so, but couple no RF back into the AC
mains.

Be sure to check everything, and that means outside as well. My dad
had a PIR light at the back door
that was a horrible RFI source. I have a older car battery charger
that is really, and I mean really nasty.
It seldom gets used, I keep it because it will start a car with a dead
battery. Because it hasn't been used
in 8 years, I haven't bothered to apply any RFI treatments. It
wouldn't be worth the time and parts. If I used
it more often I would simply fix the defective alternator or battery
in the car.

A special note, this process is very time consuming and will take
several days. Be certain to keep notes
or you will end up dong the tests several times.

And keep your notes showing each devices noise level. Equipment does
fail with age or after electrical
transients from lightning.

As new equipment is added is be sure to check it out. Check EVERY
piece of equipment that comes in.
At the very least you will know when you have a nasty RFI source and
perhaps you can exchange it for
a less noisy device.

When Will bought a new lap top we took my "Sniffer Loop" and DX398 to
the store to pick the PC. You do
get some very strange looks, but it could be very useful to avoid a
RFI problem.

Coming up next, stopping RFI once you've found it.

Terry