Solving an RFI Problem at Strawberry Hill

The story starts on Field Day, two years ago, the last Field Day that was held on the Island.

We set up at Strawberry Hill Park. That’s in a semi-rural location, and I had gone on “DXpeditions” there to successfully escape the high levels of RF noise at my Winslow home QTH a number of times before, and had mentioned this to others when the Club was floating ideas for a Field Day location.

Imagine our surprise and disappointment when the noise floor turned out to be S-7 or worse on all bands. Despite that handicap, we did still operate there; doubtless we missed many dozens of stations calling W7NPC just because we couldn’t hear them.

After Field Day passed, I thought about the noise issue multiple times, but they were just fleeting thoughts. I never did any followup investigating as to what the culprit might be.

Then one day I was out riding my bike for exercise, as I try to do several times per week. Just south of the intersection of Fletcher Bay Road and High School Road, I thought I heard a faint noise coming from a power pole. I stopped. It wasn’t my imagination: I did hear a faint noise. It sounded like something arcing.

A few days later, I returned to that spot after dark with some binoculars to confirm my suspicion. Sure enough, a faint bluish spark was visible coming from one of the high-voltage wires leading to the pole pig transformer.

I jotted down the details of the pole (the numbers on it, plus its relation to the nearest interesction) and reported it to Puget Sound Energy. And, until recently, forgot about the incident.

Prompted by a fellow club member, I decided to write down my experiences, and that meant also researching what came of my report. Well, there’s no more arcing happening at that power pole, so apparently the issue has been corrected.

That’s not a surprise. First, it was an FCC regulations violation. Second, arcing equipment is equipment ready to fail, and any competently-run utility would rather replace failing equipment before it fails, during regular working hours, than have to dispatch an emergency repair crew being paid overtime wages after it fails. Third, equipment failures in the electric grid sometimes start wilfdfires and/or kill people, and the utilities would rather that (and the associated lawsuits and reputation damage) not happen.

I have since visited Strawberry Hill park and can verify that the noise floor there is now much lower. The moral of the story is that it doesn’t always take fancy equipment, or even any equipment, to find the source of HF interference. Sometimes the only thing it takes is your own eyes and ears.

A Simple Dual Band Auto Install

Not too long ago, I bought a new car.

My old car was a mobile shack, having an HF radio mounted in it. It was great. I could stop anywhere and work HF stations all over the world. While I was driving, I could listen to my local repeaters on the VHF or UHF bands that were built into the radio. Now that I had a new car without a radio, I began to miss having the VHF and UHF bands while I drive.

In my garage, I have a collection of antenna parts. In my shack, I have a collection of radios. Surely, I could come up with an installation that would at least give me local repeaters with minimal effort.

You may not have a collection of parts laying around. At the end of this article is a list of the parts that I used and a list of parts that cost less than what I used.

Step 1: Antenna

The magnetic-mount base and triband antenna.I always start by thinking about the antenna, mainly because getting the antenna outside of the metal shell of the car greatly increases the effectiveness of your install when compared to having a handheld radio inside the car.

In my case, I had a magnetic-mount NMO antenna base laying around the garage. This type of mount is a magnetic disk with an NMO connector on the top and a coaxial cable running out of the side of the base to a PL-259 connector. The magnet holds the antenna on the roof or trunk of the car (because the car is metal).  These are great because you can replace the antenna without having to dispose of the magnetic base if the antenna becomes damaged. You can also upgrade your antenna for less cost if you decide to add bands with a different radio later.

I also had some dual-band antennas (antennas tuned for 144  and 440 MHz) that connect to an NMO mount sitting in the garage. These were perfect for this install because I was only concerned with these two bands.

I screwed the antenna onto the base and place the magnet on the trunk of the car. Then, I run the cable into the trunk, under the back seat and between the seats to the area where I want the radio installed.

The antenna is installed.

Step 2: The Radio

There are many radios from which to choose. Amongst them are several low-cost radios.

I use the door above the radio as a mic compartment. This keeps me from sitting on the mic and accidentally transmitting.

I had a Baofeng 25×4 laying around that I had not yet installed. The cool thing about this radio is that it isn’t much bigger than the microphone. For newer cars, where dash space is consumed by screens and other controls, a smaller radio will fit into spaces where a larger radio would not. If you’re going with a bigger radio, like the Yaesu FT857D, the faceplate comes off so that you can mount the radio in the trunk and remotely mount the face-plate on the car’s dashboard.

On the back of most radios, there is a SO-239 socket. Even though they don’t have the same number, the PL-259 plugs into the SO-239. Once I’ve screwed the connector onto the radio, the radio and antenna are now installed.

Step 3: Power

To power the radio, I did the simplest solution available. I took the cigarette-lighter adaptor and plugged it into the DC socket in the car. The radio is rated for 20A maximum current, so be sure that your socket can handle that current (by checking the car owner’s manual).

Refinement

This solution will get you on the air. There are improvements that could be made to make the installation more permanent and more reliable.

  1. A better power solution would be to wire directly to the car’s battery. This solution requires more effort to do in a way that keeps from letting water in. I’ll do another post on this when I do this step on my car. I’ll post pictures and include the steps that keep the power clean and the rainwater out of your car.
  2. If you want your antenna to be more permanent, there are NMO mounts that you can place right in the metal of your car’s roof or trunk lid. This requires skill with a drill and can destroy your roof or trunk lid if you don’t do it right. If I get to this point with my car, I’ll post it, along with pictures.

Parts List

For This Install

  1. NMO Magnetic Mount – http://a.co/2FO2DPE
  2. Tri-Band Antenna (2m, 1.25m, 70cm) – http://a.co/fPCQmnW
  3. Baofeng Tri-Band Radio – http://a.co/7Z2tnM1

A Cheaper Radio and Antenna Set

I have a cheaper radio in my shack that acts as a base station. A dual band antenna is also cheaper than the tri-bander above. So, if you’re looking to spend less and still have a workable solution, this parts list might do for you.

  1. NMO Magnetic Mount – http://a.co/2FO2DPE
  2. Dual Band Antenna (2m, 70cm) – http://a.co/b02ha5p
  3. Dual Band 10W Radio – http://a.co/6F32Mu2
  4. OR, the 25W version of the same radio for $30 more – http://a.co/gIaN3Wo

Radio Direction Finding, AKA Foxhunting

If you’re thinking amateur radio is just about sitting at your desk and making contacts with other hams, there’s a whole lot more to it. One of the fun things we can is as a form of “radiosport” called foxhunting. It uses radio receivers to locate a transmitter at an unknown location.

Typically, directional antennas are used to home-in on a signal, allowing you to get a bearing, move in the direction from which you think the signal is coming, then listen in and adjust your bearing until you (hopefully) arrive at the transmitter location. The first one to find the transmitter wins!

This activity can be done on foot or with the use of vehicles to allow quick movement toward the transmitter. In the case of a mobile operation, you either use RDF antennas in/on the car or pull over and stick an antenna out the window every so often.

You can build your RDF gear or buy it pre-made or in kit form. Check out this page for some resources or do a web search to learn more.

RDF is used for more than just fun. It is also used to track wildlife, locate sources of interference (1, 2), find stolen cars (LoJack), or for search and rescue. If you ever had reason to track radio frequency interference (RFI), it would sure be nice if you’d already had some experience with direction finding so the process was familiar.

Here’s a good video that shows a competition in progress and gives a good idea of how the process works. It was produced by KN4AQ, who has a series of YouTube videos under the title HamRadioNow.

Here’s a link with video of a practical use of RDF for tracking down power line noise – the noise coming from some broken piece of equipment on a power pole (like a cracked insulator causing arcing).

 

Additional Reading:

https://en.wikipedia.org/wiki/Transmitter_hunting

https://en.wikipedia.org/wiki/Direction_finding

http://www.homingin.com/ – all about foxhunting