More information on RF noise

By Les Cobb, W6TEE

This article is reprinted from the June 2000 issue of Worldradio.

Let's start off with HF mobile antennas. A while back, someone wrote to me that they had a stick-type mobile antenna that had developed an intermittent connection at the base. At that time, my only experience along those lines was with a 20-meter stick that I won at a hamfest years ago, but never used until about four years ago. This one is no longer manufactured, but is copper wire-wound fiberglass with no top whip. It developed an intermittent after only a day of use on a coast-to-coast trip. Inspecting it, I could see a nick in tile wire through the shrink tubing, about an inch above the bottom metal fitting. Since there was no damage to the tubing, it had to have been a manufacturing defect. I was able to repair it in the motel.

But recently, I tried to use a 40-meter stick that I bought at a swap meet in a bundle of three such antennas for different bands. It also had an intermittent connection. I cut away the plastic shrink tubing from the bottom metal fitting and saw that the copper wire had been flattened against the fitting, but not tinned nor soldered. The metal under the wire had been tinned. I fixed this, and I am about to put a short length of shrink tubing over the repaired area. I assume that the original owner had no problem with this antenna until the copper wire started to oxidize. The plastic shrink tubing would have clamped the wire against the bottom fitting. This would have been imperfect, but maybe not noticeable. Has anyone else had experiences like this? Was this just a one-time manufacturing error, or did they expect the mechanical connection to last?

The old noise subject refuses to die. Not only was there e-mail between some of the noise-plagued Hams that I mentioned in April, but there were some new comments too. I'll try to summarize. Greg LaHaie, K7YDL, researched the Ford noise problem phone number that we printed in the April column. At this writing, I haven't heard how he came out with the fuel pump RFI kit on his Ford Explorer. But Monte Chamber, KO6XI, who raised this question in the first place, had the kit installed on his 2000 Mercury Marquis. The dealer had no idea what Monte was talking about until he showed them the eight faxed pages from Arnie Nielson at Ford. But it didn't solve Monte's problem. The noise doesn't go away until he pulls the fuse on the engine electronics. But in killing the engine, it still takes three seconds for the noise to drop off.

Gary Harrison, KQBC, QCWA President, also was going to try the Ford fuel pump RFI kit on his Ford Explorer. Jim Walch, W7LVN, Q CWA General Manager (another plug!), elected to listen to his fuel pump on his '88 Bronco rather than drop the tank, etc. Vern Chinen, W6IC, asked me for the Ford noise information before the April issue came out. To save you looking back, Arnie Nielson at 313/845-7565 is their RFI guy.

Carl Fisher, WQHIK, commented on ground loops that we mentioned in February. He talked about a classic case where a two-way radio had overwhelming noise until he used insulated washers to bolt down the radio. He also commented on 10-meter ignition noise on his 2000 Buick LeSabre that only developed after a very few thousand miles. After checking that all the usual remedies were in place, he was beginning to suspect a bad spark plug.

Bob Snowman, KRIB, would like to give out New England counties on CW mobile, but has too much noise with the engine running on both his 1994 Jeep Cherokee, and his 1994 Toyota Tercel. He is looking for specific experience in solving noise on either vehicle. I will pass on any comments, but I feel that there are few, if any, vehicle-specific fixes (unless it is on Ford fuel pumps!). The first thing to do is to run through the standard noise tests and remedies listed in any good mobile book.

Chuck Flanagan, W5GK, saw our April column in a sample Worldradio copy, and is going to subscribe. He said that his dealer knew all about the fuel pump RFI filter for his 1997 Lincoln Town Car, but Chuck went with the Clear Speech DSP speaker. He says, "'The Noise is gone and I'm HAPPY!"

When I put together my April colum, I was just leaving for two consecutive Ham Radio campouts at Quartzsite, Arizona, the same as last year. I went into more detail in the June 1999 Worldradio about the following two groups, and the Winter RV influx at Ouartzsite, but I'll stick to the short version this time.
Driving to Ouartzsite, I talked briefly each day to my friend Ross Stevens, WOXJ, on the 20-meter Elks Net. At Quartzsite, I camped with the Sam's Radio Hams, 27-30 January and at the Ouartzfest 2000, 01-06 February. Sam's Radio Hams is a Southern California Chapter of the Good Sam RV Owners Club and they were there on a monthly campout. The Quartzfest is an informal RV Hamfest that draws Hams from all over the U.S. During both events, I was able to meet with some serious mobileers and RVers and hear some interesting talks. While driving home, I checked into the Sam's Radio Hams 40-meter net and heard about the further travels of some of their members. See my web page listed below for a link to a longer version of this trip, which includes the Quartzfest 75-meter antenna shootout.

When I got home, I had a nice e-mail waiting from Paul Owen, W6UHF, who heard me in QSO, driving to Ouartzsite, and recognized me as being responsible for this column. Unfortunately for HF mobile, I was on 2-meter simplex at the time!

I'm now leaving on another trip which will include the Mt. Vaca Radio Club annual Spring desert trip, at Golfs, California, followed by a monthly Samís Radio Hams campout, near Merced, California, which is on my way home. I expect to be mobile on 40 and 20 Meters and will report anything new next time.

Let me hear from you on any HF mobile subject! Send e-mail to lcobb@compuserve.com, or write: Les Cobb, 4114 Horgan Way, Sacramento, CA 95821. More at http://home.pacebell.net/lcobb/.

KN

 

 
 

Lightning Protection

Gerry Crenshaw, WD4BIS

 
As we approach the spring and the peak of storm season, it is time once again to think about lightning protection, both personal protection and for our equipment.
Lightning, What is it?
Lightning is best defined as a massive complex AC surge with a typical frequency of about 20 to 500 Khz. It is not a DC surge as many people think. Lightning usually takes the form of a pulse that has a rise time of about 2 microseconds and a decay time of between 10 to 45 microseconds. If you use the frequency formula of f=1/t you will find that the initial pulse is about 1/.000002 or 500000 hertz (500 Khz) and the decaying pulse is 1/.000045 or 22222.222 hertz (22 Khz). The IEEE "Standard" strike is defined as a 8 us (rise time) by 20 us (fall time) with an average current of 18,000 amps for the first stroke and half that for the second and third strokes. An average strike is three to four strokes. Because we are dealing with an AC waveform, DC resistance to ground is not nearly as important as the INDUCTANCE to ground.
Any bend or coil in the ground system adds inductance. For this reason, any run to ground must be as straight and free of bends as possible. Gentle bends are preferred to right-angle bends. Since we are dealing with a complex AC wave form with rapidly changing frequency, the majority of the currents is carried near the "skin" of the conductor, so the more surface area, the better. Wide copper "straps" work better than thick round solid cables. Multi-stranded cables (the more strands the better, welding cable for example is preferred to AC Cable) work better than solid cables. The green wire AC ground in your house or apartment is USELESS as a ground for lightning protection. It has lots of bends, is coiled in places, and is usually quite long (or resistive), so this presents a huge inductance to the pulse.
Most damage to our homes and equipment is not caused by a direct strike but by huge "induced" voltages on conductors from a nearby strike. If you remember that only an AC waveform can cause induction, we then are dealing with the phenomena of EMP or Electro-Magnetic Pulse.
The Station Ground for Lightning Protection
If there is one rule of grounding for lightning protection, it's USE A SINGLE POINT GROUND SYSTEM. All of the coax, rotor cables, AC wiring, wiring boxes and telephone wiring (if any) should come together and be bonded together at one single point in the equipment area. Having multiple places where these items go to ground leads to a condition known as a ground loop. Each ground point in a multi point ground will have its own resistance and inductance. This leads to different voltage levels and currents seeking to go to ground. Lightning seeking the easiest path to ground will flow around these various ground paths until it finds the best path for itself. Ground loop currents flowing around these other paths are usually the cause of equipment damage, not the lightning strike itself.
Surge suppressors and other treatments
 
After you have a good ground established, then it's time to investigate surge supression systems. There are several commercial surge suppressors on the market that seem to work well. Transi-Trap, Polyphaser and MFJ offer "in line" coaxial devices. Most of these are based around a "gas filled" spark gap that will protect your equipment. These devices will literally kill themselves to protect your equipment. After a severe strike they may have to be serviced or replaced. Most offer a replacment element for this reason.
Treatments to the telephone and AC wiring in the shack should consist of placing M.O.V devices or transient suppressors across the line. S we will be dealing with induced voltages, a single device is not enough for the AC wiring. A device from Hot to Ground, Hot to Neutral, and Neutral to Ground affords the best protection.
In the Field
Many of us do storm spotting for R.A.C.E.S, so what is safest place while storm spotting? The enclosed car. Because it is isolated from ground by the rubber in the tires, it's usually the safest place. The car is wrapped around your body in what is termed as a Faraday Cage (a sheathed electrical cage isolated from ground). In the event of a direct strike, the car will instantly come up to the same potential as the strike. It's the differences in potential that cause damage and injury.
One of the Ace storm chasers for this area is K5KJ. He often tells the story of a lightning strike to a telephone pole near where he was parked (about 20 feet). Even though the strike damaged the majority of the radio equipment in the car, he managed to get the car started and drive away without injury.
If you are out of the car, avoid tall objects such as trees, power and telephone poles, and stand with your feet close together. This avoids having a difference in potential of several thousand volts between your feet and your heart.
The best way to avoid injury and damage would, of course, be to disconnect the equipment and not use it during a storm. However in our role as emergency communicators, we are often called upon to communicate in less than ideal conditions. Please remember that equipment is replaceable, but YOU are not. Take all possible precautions when communicating for R.A.C.E.S or Civil Defense activities this spring.
The best way to avoid injury and damage would, of course, be to disconnect the equipment and not use it during a storm. However in our role as emergency communicators, we are often called upon to communicate in less than ideal conditions. Please remember that equipment is replaceable, but YOU are not. Take all possible precautions when communicating for R.A.C.E.S or Civil Defense activities this spring.
Safe Storm spotting and Good luck, Gerry WD4BIS Copyright 1996 Gerald Crenshaw WD4BIS. All rights are reserved.

HOG HEAVEN (OOPS) HAM HEAVEN

BY

Emmett H. Goodman, WD4GOL

This article first appeared in the October 1997 issue of CQ de WA2LQO. It was so good I decided to repeat it here. The Editor.

Two farmers were standing over a hog pen watching two fat hogs wallowing in a big mud hole filled with water. One farmer said to the other, "Those two hogs are in HOG HEAVEN!"

Well I'm going to tell you about a Ham, who in 1938, was already in his own HAM HEAVEN!

I was still employed in the auto repair bays of that super dooper automotive repair facility referred to in my last tale, "160 Meters, The Easy Way", As I walked in about 8:45 AM after dropping off my XYL at the Hudson Hosiery Company ,where she was dragging down over $30 per week, which was very good wages in 1938, Why do you think I married her? Anyway, Mac, W4HGV, my boss said, "Since you are interested in ham radio, if we have caught up with our work by lunchtime, why don't you take the afternoon off and go visit a ham station that you will not soon forget."

So, after lunch, I was following a map supplied by Mac to the 5 acre supply storage yard of the Duke Power Company north of Charlotte (NC) city limit. As I pulled through the gate of the eight foot high chain link fence to find a parking space before the little office, I was amazed to see the stacks of 20, 30, & 40 foot poles, transformers, automatic and manual switches, rolls of all sizes of wire and cable insulators of all shapes and sizes. Everything necessary to keep the city of Charlotte lighted up!

As I parked my car and got out I looked up and saw a stacked five element 10, 15, & 20 meter beam atop the tallest power pole that I had ever seen running up besides the end of the building. I also saw a lot of two wire ladder lines running out to a lot of 30 foot poles with insulators and wires running between them as far as I could see.

I walked through file door into a large room and met file young ham, a graduate of the University of North Carolina, where he had obtained his Electrical Engineering Degree. He had been hired by the Duke Power Company as a yard clerk to check the supplies going out on the maintenance trucks in the morning and checking them again on their return in the evening. You are right, to ask, what is a college kid, with a degree, doing working as a clerk in a power company supply yard? Well, you must remember the time frame that we are talking about. In the late 30's the country, under FDR, was still recovering from the GREAT DEPRESSION! You were lucky to get any kind of a job. I was just working part-time But just wait until I tell you of the "perks" that went with the job.

Tom, not his real name, had talked to the powers that be, with the help of his father, who just happened to be a large stock holder of Duke Power, into letting him install his ham station in the office. Reasoning that they could supply communications in the event of an emergency. They bought it!

Over in the comer of the room was, not one, but two homebrew Carolina kilowatts, mounted in two six foot rack & panel cabinets. One xmtr on 10, 15, 20 meters. The other on 75 meter phone. On top of the two desks were two National HRO ham receivers, the kind that had file big bandspread dial in the middle of the front panel that you could spin and just listen to the stations just roll in.

What? You don't know what a bandspread dial was? Well the ham receivers of that day used either a two-speed planetary drive, the mechanical way or file electrical way of putting a small tuning capacitor in parallel with the main tuning capacitor to cover a 2 to 1 frequency range. I believe the HRO used the mechanical way.

The 10, 15, 20 meter xmtr could either be used to feed the beam antenna with a coaxial cable or feed two rhombic antennas that were feed by those funny looking ladder lines that I had seen going to those 30 foot poles that support those 210 foot legs of the diamonds. One rhombic was directed to Europe and the other to South America.

By means of electrically operated relays he could change the direction of the rhombic facing Europe to work Australia and New Zealand The 75 meter kilowatt fed a half wave dipole strung between two 40 foot poles.

As I walked in about 1 PM, 20 meters to Europe was wide open and the rhombic antenna had a slight edge over the beam on receiving. On transmitting the two antennas were about equal. He was working an Irish station in Dublin and as soon as he signed with him a station in Oslo called him. I forgot to tell you that the back wall of the room was filled with antenna change-over relays. He could transmit on one antenna and receive on the other. This boy was good!

He signed with the Norwegian station after getting an S9+ report. Then he quickly switched over to the South American rhombic and by golly there were a couple of missionaries in Brazil with traffic to the USA. Tom quickly contacted them and took their traffic. This hamming went on all the rest of the afternoon until the equipment tracks began to return and Tom had to go back to "work", hi! This was truly HAM HEAVEN!

At contest time he rolled in a cot and set up a hot plate, invited a brother ham to join him and the two of them worked around the clock.

But Tom's ham heaven was short lived. About eighteen months after my visit Tom was hired by the city of Charlotte as chief engineer to design to supervise the installation of a modem two-way radio system for the police and fire departments At

least he uitlized his E.E How he worked ham radio into his new job is another story. (Watch for it,) WD4GOL

KN

ABOUT THE AUTHOR

Emmett holds a General class license. He will celebrate his 84th birthday on September 26, 1997. Have a happy one Emmett!! He can be reached at the following address:

Emmett H. Goodman, WD4GOL 360 Diane Ct.

Casselberry, FL 32707-3023

 
 

 

 

EDITORIAL

Here's a little story that's a plus for the younger generation.

The tube that goes from the hot water supply to the faucet of the sink in my upstairs bathroom sprung a leak. Not wanting to call in an expensive plumber to fix it, I decided to fix it myself.

After a small struggle I managed to get the tube off and I went to the local hardware store to get a replacement.

When I arrived at the store all the clerks were busy and one young man was sitting on a stool by the cash register, obviously having his lunch.

So I was standing there with the tube in my hand waiting for someone to get free to help me.

Without a word the young man eating his lunch got up and went away. In a couple of minutes he returned with the replacement for my damaged tube.

He handed me the tube and proceed to ring up the sale. Now that is what I call service!!!

The Editor