The RFI snip hunt
 

I may have mentioned my quest to find and stomp RFI.
I found a very handy tool. The dual purpose pill bottles,
the ones with a single top that can be child proof, or
non child proof by simply turning the cap over are great
for a variety of RF uses. I have used them for coil forms
and by mounting tow pill bottles end to end, you can
lift it away from the metal case wall.

I wound about 24 turns of solid #26 insulated hook up wire
on one pill bottle. I drilled ~.1" holes to carry the wire to
the inside of the bottle and mounted a BNC female connecter
in the lid. By drilling a hole in the bottom of another
pill bottle I can feed coax and have a nice holder keeping
my fingers away from the coil.

I use RG-174 to connect the probe to my DX398. With a
4' piece of coax I am set to check every device in our
home for RFI.

I built a similar unit with only 2 turns for hunting higher
frequencies. And I built a probe in a larger sharpy with
a 300uH radial inductor to sniff inside of equipment to
find the exact noise source.

While I used BNC connectors, there is no reason why a
dedicated probe with RG174 terminating in the approbriate
connector couldn't be used for cast savings. Since I had
the BNC connectors in my junk box, and because I
wanted to be able to use a double male BNC to mount
it on my HT or scanner I decided to go to the additional
trouble and "expense".

I found an allusive "pop" RF source in one of the battery
operated smoke detectors.

Every time I find another noise source and clean it up, I can
receive ever weaker signals. Of course I don't have any such
success with my neighbors.

These little probes added to my 400MHz mini yagi with a
PRO34 allow my to farily quicky find internal and external
RF noise sources.

And while I use a DX398, there is no reason why any portable
couldn't be used. A desktop receiver will also work, but a portable
is so much more convinient.

Be sure to check the incoming telephone line, CATV etc.

While a few odd sources only emit RF on one frequency, most
are broadband jammers.

Terry

The RFI snip hunt
 

Telamon wrote:

A small loop like the one you built is a classic H field sniffer I have
used to look for RFI problems in switching power supplies. You could
also build a short E field sniffer antenna by extending the center
conductor of the coax a few inches (about 3 inches would be good). Use
shrink sleeve over a heavy gauge wire would make a good E probe.

--
Telamon
Ventura, California

A friend sent me a link to a very interesting pdf,
www.conformity.com/0211field.pdf .
The part about using the tracking signal generator and a directional
coupler to find unexpected resonances was very useful.

Terry

The RFI snip hunt
 

In article . com,
wrote:

Telamon wrote:

A small loop like the one you built is a classic H field sniffer I have
used to look for RFI problems in switching power supplies. You could
also build a short E field sniffer antenna by extending the center
conductor of the coax a few inches (about 3 inches would be good). Use
shrink sleeve over a heavy gauge wire would make a good E probe.

--
Telamon
Ventura, California

A friend sent me a link to a very interesting pdf,
www.conformity.com/0211field.pdf .
The part about using the tracking signal generator and a directional
coupler to find unexpected resonances was very useful.

I never did that. I did use the tracking generator and spectrum analyzer
to sweep the EMI filter sections that were a part of the supply to see
how well they worked attenuating EMI. I made improvements in the filters
based on that information.

That PDF is a very good primer on EMI / RFI problems and at the time I
was doing that work I had to figure out the strategies outlined in that
document myself with the exception of using using the probes /
directional coupler as a type of grid dip meter. This would be an
excellent proactive technique that I could have used when I was doing
that kind of work years ago.

What he recommends for a sniffer loop an inch in diameter in figure 2 is
over kill in my opinion but would be very well worth the effort if you
were to make a loop larger than a few inches in diameter for hunting a
more distant source than poking around the insides of a box of
electronics. I don't think a BALUN would make much of a difference in
what a 1 inch diameter loop with a split shield would pick up inside a
box.

You can tell that this document was written years ago because it states
Scott Roleson works for HP, which is now Agilent.

Very interesting pdf document, thanks for pointing it out.

--
Telamon
Ventura, California

The RFI snip hunt
 

betsy meyers of nbc fame once phoned me.I picked up my phone and I
said,Who is this? As soon as that Commie Lieing woman said her name,I
slammed my phone down and hung up.Dont you EVER! phone me anymore!,
betsey meyers!!!!
cuhulin