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Re: [RFI] FW: Topband: Exciting noise sources (Tim Duffy K3LR)

To: <rfi@contesting.com>
Subject: Re: [RFI] FW: Topband: Exciting noise sources (Tim Duffy K3LR)
From: "Frank Haas KB4T" <kb4t@arrl.net>
Reply-to: kb4t@arrl.net
Date: Mon, 28 Mar 2011 11:52:04 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
While this lengthy story details a painfully long and (luckily) successful
power line noise investigation, it points out the value of good location
equipment. Had the searchers been equipped with even marginally better gear,
they likely would have found the source more quickly and efficiently. 

The ideal collection of gear is that made by Radar Engineers. RE gear
consists of all the tools needed to pinpoint a source at least to the pole
if not down to the nut, bolt, bond wire or device that is the source. 

I've read varying reports about the effectiveness of the MFJ Noise Meter. I
admit that I'm spoiled by my complete set of RE tools. However, I fail to
see how something so simple as the MFJ box can be very effective. 

When hams ask me what I recommend, I suggest using an all band receiver
capable of AM mode reception throughout its range equipped with a decent
signal strength indicator and a BNC antenna jack. Use a directional antenna
to get starting bearings. An HF beam, if available may help at the outset.
Carry a decent external attenuator with an extra cable so the pad can be
inserted in the antenna line as you get closer to the source so a very
strong source doesn't swamp the receiver.

Use the AM Mode at all times when searching for power line interference.
Start listening at the affected frequency and take bearings. Pursue the path
of the strongest signal. If the affected frequency is on HF, you might need
something like the National RF HFDF Vector Gun (something I'm still
evaluating and getting fairly good results.) 

The majority of real power line interference sources can be heard at VHF and
low UHF frequencies as you approach the source (within a 1/4 mile
typically.) A few can't be heard above 8 MHz and REQUIRE something like the
National RF HFDF Vector Gun.

Having a true directional antenna makes locating the offending pole

Once the offending pole has been found, a good physical inspection with a
pair of binoculars is a good first step. Nearly 50% of the real power line
issues I find are the result of poor construction practices. Bond wires
(often bare solid copper wire) situated too close to ungrounded hardware or
wrapped around the edges of other devices on the pole can be incredibly
strong sources of spectrum blanketing interference. I have resolved many
interference cases just by having these poorly placed wires moved 2 inches
away from anything else on the pole. 

The neutral wire and all connections to it can also be a strong source of
RFI. The physical inspection may show corroded or loose connections that can
be very problematic. 

If working with a crew, the use of an insulated stick to poke, gently tug
and nudge equipment safely can often quickly reveal loose hardware and
fractured devices. Hammering in bond wire staples is always a good practice
with wooden poles. Loose hardware is a very frequent source of interference.

If the physical inspection and tugging doesn't reveal a source, then a step
by step troubleshooting process is needed to pinpoint the source. Opening
switches to transformers can help isolate lightning arrestors and other
equipment. Ultimately the process should narrow down the offending device.
For this to be effective, one must be CERTAIN that you are working on the
source pole. 

As the story presented here clearly shows, time can easily be wasted
attacking the wrong pole. The goal of any searcher is to be absolutely
certain that the actual offending pole or pad mount device has been located.
This can only be done using good direction finding tools. I don't believe
the MFJ box qualifies. 

There are so many "all band" capable receivers available today, it should be
easy to find one. Any portable 2 meter or even a UHF yagi antenna will work
fairly well. A good attenuator, cables with properly installed connectors
are also requirements, in my opinion. If you are going to spend the time to
pinpoint the offending pole, equip yourself with the best tools you can
afford and your search will take less time and hasten resolution. 

Please don't kick, sledgehammer or tamper with any pole or any "down guys."
Leave this part of the process to the utility crew. You can be injured or
arrested and your noise problem will live on indefinitely. Cooperate with
your utility by always being patient and polite. In the end, you will make
new friends who will help you in the future and your noise issues will be
resolved as quickly as possible. 

Good hunting!


Frank N. Haas KB4T
Utility Interference Investigator

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