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Noise Abatement

Alan Applegate (K0BG) on February 27, 2003
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One of the prevalent subjects in the comments from my first two article has been noise abatement. -- In other words, how to make a vehicle as quiet as a base station. What appears below may be a repeat of some of what went before, but it is an unavoidable consequence.

There are two aspects to noise abatement; the reduction of existing noise, and keeping what noise there is remaining out of our circuitry. I'll do my best to keep these as separate subjects, however the reader should keep in mind they are intertwined and nearly inseparable.

Radio frequency noise (RFI) is generated by just about every mechanical and electrical device in the modern automobile, truck, RV, or motorcycle. Ignition systems, fuel injectors, DC motors, alternators, relays, fuel pumps, engine computers, airbag control circuitry, defroster grid wires, you name it, it generates RFI. From time-to-time, each and every one of these devices, and a few I haven't mentioned, all require some type of noise abatement. And make no mistake about it; there is not a universal cure, not even the world's best noise blanker. Fact is if you have to use your noise blanker to "fix" a noise emanating from your vehicle, you need to do more suppression work.

If there is a cure all, it is the ubiquitous ferrite core. Since they have come into general use, literally billions have been used to control RFI in every form of consumer electronics you can think of, and even in automobiles. We amateurs use them in a variety of ways such as baluns and chokes. Ferrites come in a large range of sizes and shapes. One commonly sees toroids, round bars, flat bars, and tubular shapes cut along their axis, better know as split-beads.

And they come in a large range of mixes too. Depending on the application, permeability requirements, frequency range, and temperature needs, one can choose from near 600 different mixes from dozens of manufacturers. With this many to choose from, it is important we know what we're going to use them for. Before we go any further remember this; it is the frequency of the RFI we need to control not the frequency we operate on which determines the best mix.

There are three popular mixes, which we need to be concerned with. They are: Mix 43 which has an operating range of .01 to 1 MHz (best for all around use); Mix 77 which has an operating range of .001 to 2 MHz (marginally better for 80 and 160); and Mix 61 which has a range of .2 to 10 MHz (marginally better for VHF). Ferrites work because they get very lossy at frequencies outside of their frequency range. For example, at 10 MHz Mix 43 has a loss of about 80 ohms and if installed on a low impedance circuit, it will act like 80 ohms in series with the offending RFI. They are simple to install, they literally snap on, and the best part is you don't have to open the circuit to install them. I digress.

Opening circuits to install capacitors and/or chokes can be the proverbial sticky-wicket. Aside from the warranty issues, it has been my experience that beads work just as well, cause less problems, and the best part is they are easily removed to be reinstalled on a newer vehicle.

Split beads commonly come in 1/4", 3/8" (8mm), and 1/2" inside diameters, and have a plastic outer case, which holds the two parts and firmly snaps together. As long as they fit over the wire and will snap close, it is unimportant that they be a snug fit, with the possible exception of plug wires (more on this in a moment). They should be placed as close to the offending device as possible to minimize RFI leakage. So let's look at a few real-world applications.

Fuel pumps (especially on 2001 and earlier Fords and Toyotas) are particular troublesome because they are not rhythmic and therefore hard to pin down. And they are so noisy it sometimes takes two or three beads to quiet them down. You'll need 1/4" beads for this application.

Electronic fuel injectors are controlled by the engine management system, and although they are well shielded, some RFI does leak out. The RFI is generated on both the rise and fall of the control voltage creating a rhythmic double tick that is easily detected. You'll need 1/2" beads for this application.

A few years ago, if someone told me I could use split beads over my plug wires to control RFI, I would have argued with them. But I tried it, and I was amazed at the effectiveness. You'll need 3/8" (8mm) ID beads for this application. They need to be installed as close to the coil pack (or distributor) as possible. These will be a snug fit and they need to be to keep them in place.

Those critics, who say placing beads on spark plug wires is not a good practice, haven't done their homework. The distributor has disappeared in favor of computer control, coil packs, and plug wires, to the latest iteration, coil-over-plug (COP) technology where there isn't any plug wires at all. But in most cases, inside of that COP assembly is a toroid core. Nonetheless these units can leak RFI over their control wires and split beads work well in this application.

Personally I would try split-beads on any circuit I thought was causing RFI. It is doesn't work, it can be easily removed. Again, the beads should be placed as close to the offending device as possible to minimize RFI leakage.

Low impedance circuits are a must for mobile installations whether or not you use split beads to control RFI. Even a few tenths of an ohm is enough to allow stray RFI to invade equipment. This is why I recommend at least size 8 AWG. I don't run an amplifier mobile anymore, but I still feed my trunk-mounted fused distribution point with number 6 AWG. Attached to this fuse block is my remote mounted Icom IC706 MIIG with its companion AH-4, and a one farad capacitor which keeps the 706 from resetting when I start the vehicle. Both + and - leads are beaded close to where they pass though the firewall, and again at the fuse block.

The fuse lock I used was purchased from Radio Shack, although a lot of automobile sound suppliers have similar items. [Many hi-fi stereo shops carry these as well. - ed.] Mine has 4 fuses tied to a common supply rail, but I attached the positive lead from the battery on what would normally be a feed, and fused it with a 50-amp fuse. This then feeds the common rail, and I use smaller, appropriate sized fuses for the IC706MIIG and one farad capacitor. The open port holds a spare fuse. All of the connections are covered by a clear plastic lid. Incidentally, fuses are available with LED blown fuse indicators for those who have to have the ultimate gadget.

The next phase in noise abatement is bonding, or strapping if you please. Not only does it help reduce RFI, it also aids in lowering the ground losses, which directly affects antenna efficiency. I make up several different lengths of RG58 shield (you can buy copper braid at some hardware stores if you don't have any old RG58 laying around), and attach solder lugs to each end. I use lugs, which have built in star washers to make sure they make good contact. Where there is a chance they will be abraded, I use the discarded coax vinyl cover to protect the braid.

I use self-tapping sheet metal screws to secure them to the frame and/or body parts. Care must be taken drilling into doors, etc. because you do not want to interfere with any existing hardware or electrical circuitry. I use stainless steel hose clamps to attached straps to the exhaust and tail pipes. Doors, hoods, trunk lids, pickup beds, and inner bumper supports are all targets for bonding.

Here's a caution: If your car has a steel gas tank (mine is plastic and they don't need bonding) use great caution in bonding the tank to the frame. While it is possible to safely drill outside the roll welded area, I don't recommend it. Your safest bet is to use the clip-on ground lugs available at most hardware stores. They are typically located in the TV accessory area. These can be safely attached to the peripheral of the tank. And, when attaching the lugs to the body or frame, make sure you know what's behind that screw. Safety first always!

The last item I want to cover is static discharge. You hear static discharge during rainstorms, and sometimes when it snows. It slowly builds up to a crescendo until the static is discharged by a lightening strike. -- One hopefully not to your antenna. You can't control nature, but you can cure static discharge from your vehicle and antenna to a point. The corona ball at the tip of most vertical antennas is there for two reasons. During transmit; it minimizes the high-voltage that would otherwise "leak" from the pointed end of the whip. This is, after all, the highest voltage point on the antenna. During receive it theoretically limits static build up on the antenna, but in reality, it doesn't do a very good a job of it. Adding insult, revolving tires, and axle parts add their part to the static build up on your vehicle and antenna. Fortunately, there are a couple of things you can do to lesson the impact.

First, if your antenna is not matched with a unun, auto-transformer, or inductance matching coil, it behooves you to DC ground your antenna. This is easily done with a small RF choke designed for the purpose. Even a 10 K ohm resistor across the antenna terminals will do the trick.

You also need to get the static off the surface or your vehicle. In the old days, amateurs used to put graphite in the tires and use special bronze contact springs inside the wheel bearing cups to minimize the problem. Nowadays, tires already have a graphite coating, and the bronze contacts have been replace by preloaded, high-metallic content disc brakes. There is an additional way to minimize the static. Enter the static discharger, or drain if you please.

Airplanes have used these devices for ages. They're attached to the edges of the wing and consist of graphite-impregnated fiberglass enclosed in a protective vinyl sheaf, with a hint of the material out in the air slip. They effectively drain the static from the surface of the plane, a necessity given the vital nature of the electronics therein. And you can make one for your car a lot cheaper than the $50 to $100 they cost at the airplane parts companies. Here's how I did it...

I used an 8 " length of 1/8" stainless steel, vinyl covered aircraft cable available at just about any hardware store. On one end I stripped 1/2" of the cover off and crimped and soldered a wire lug to it. The other end I stripped back one inch and flayed out the individual strands purposely to make the ends stand out. I screwed the lug onto the frame extension at the rear of the vehicle so about 3 inches stick out past the bumper. It's been on the vehicle for two years and no one has asked what it is for. Does it work? Yes it does! 10-meters has always been a problem for me, because as soon as I got over 10 or 15 miles per hour, the static built up to S4 or S5. That ceased when I installed the drain. Trust me folks, this isn't an April Fool thingy, it actually works!

The old adage "an ounce of prevention is worth a pound of cure" fits mobile operation very well. I must have spent a pound of prevention, as I have virtually no noise from my vehicle, save for 18 MHz (17 meters), which is a natural noise peak frequency. And then, less than an S-unit. Nowif I could only get all those other cars, trucks, and power lines quieted down, I'd be in hog heaven (if you get the pun).

Alan Applegate, KBG
Roswell, NM

Needed addresses in alphabetical order:

Amidon, Inc.
250 Brigg Street
Costa Mesa, CA 92626
Cores, split beads, rods, assembly kits, glass tape, etc.

Palomar Engineers
PO Box 462222
Escondido, CA 92046
Cores, split beads, RFI kits, RFI Tip Sheet

RF Part Company
435 S. Pacific St.
San Marcos, CA 92069
Split Beads,

Surplus Sales of Nebraska
1502 Jones St.
Omaha, NE 6810
Split Beads, RF tubes including sweep tubes

Member Comments:
This article has expired. No more comments may be added.
Noise Abatement  
by VE6XX on February 27, 2003 Mail this to a friend!
Greetings All: Alan, once again we are indebted to you for your succinct & technically accurate treatise on this subject. I especially was delighted to see you mention static discharge wicks for vehicle static reduction. It is the first time I have seen the issue raised for amateur mobile operation. I can't endorse the use of drill point or self-tapping screws for attaching bonding straps as they are usually plated & galvanic action turns them into diodes with all that implies. I usually weld a stud to various items & secure the bonding straps with a nut & toothed washer. However, I have never tried using self-taps, & doubtless you have, so if they actually work......
The greatest boon to modern amateurs has to be ferrites, & especially the "snap-on" variety. I used a pail of them to remove the RFI from a helicopter last year, earning the undieing gratitude of the owner as a result! I question the efficacy of stainless steel hose clamps for bonding to exhaust pipes. Can one actually get a low Z connection & what about the dissimilar metals problem? Here again, the welder is my greatest ally! I realise not everyone is willing or able to attack the vehicle with the venerable flame wrench, but the question of a low Z connection never arises! Thanks again Alan, I always read your treatises with great interest. They are an oasis of fact in a desert of misinformation.

RE: Noise Abatement  
by K0BG on February 27, 2003 Mail this to a friend!
Thanks Brian. The tail and exhaust pipe on my car are stainless steel. And although they have welded-on brackets, I opted for the clamps as this is how most folks would connect the wires. As I stated, I use connectors which have built-in star washers. I cleaned the spot where the connectors were going to be with my moto-tool. So far, this has worked. I occasionally check the clamps to make sure they are still tight. But you are correct, the real way would be to weld on a stud.

Alan, KBG
Noise Abatement  
by NA4IT on February 27, 2003 Mail this to a friend!
Very good article, well written and very informative! Thanks for the good work and sharing your knowledge!
RE: Noise Abatement  
by K8JDC on February 27, 2003 Mail this to a friend!

From your article, it sounds like the static wick is positioned so that the frayed ends are essentially just sticking out in the air behind the vehicle. Is this correct? When I started reading that section, I was thinking the frayed end might be left to drag the ground and discharge static by contact or something. Can you elaborate on how this works to reduce static charge on the vehicle? Thanks...

I just made my first real trip with mobile HF capability from Ohio to Florida and back. It was a fun experience and although I did not have any particularly bad noise issues in my vehicle, I'm always looking forward to "making things better".

Noise Abatement  
by N3QT on February 27, 2003 Mail this to a friend!
Thanks yet again!!!

1.) I use a small kitchen dish rack made from plastic attached over the remotely mounted 706, a breathable turtle schell. It keeps the "inadvertantly tossed" package from smashing the radio.

2.) I tried a large foam fishing bobber glued to the end of my whip for static discharge "release" or prevention. I have to try your method. What the hey... my wife already refuses to ride in the nerd mobile.

TKS ES 73, John de N3QT
RE: Noise Abatement  
by K0BG on February 27, 2003 Mail this to a friend!
I tried using several forms of "dragging" ground straps. None worked well and in one case added to the noise.

The static line sticks out into the air stream behind my car about 3" or so. To be truthful, I wasn't sue it would work. My first try used a banana jack so I could remove and replace it easily. After several days of using it, and then not using it, I came to the conclusion it did indeed work. It is not a magic cure all, but one small piece in a big pie called noise abatement.

Alan, KBG
RE: Noise Abatement  
by K0BG on February 27, 2003 Mail this to a friend!
For those looking for a good corona ball look here:

They have a $25 minimum plus shipping, but they make just about anything you would want in the way of corona balls. They even make float balls which can be used for corona balls for homeBrew verticals. Or a nerd mobile!

I'm going to be talking to the Texas Bug Catcher people at the Midland Hamfest in March, and I hope to convince them to start stocking the 1" aluminum ones. We'll see.

Alan, KBG
Noise Abatement  
by JA2WWE on February 27, 2003 Mail this to a friend!
Must begin with radio with good filtering to start with- Alinco is poo poo..........Yaesu is #1. Then use above comments- But be wise, some radios are so bad to begin with, you need to get head doctor to cure you before buying-

Noise Abatement  
by K0PP on February 27, 2003 Mail this to a friend!
Alan and I have been friends for many years and he knows of what he speaks. I spent five years in an over-the-road semi and therein lies a whole new set of noise-related problems. For starters, many trailers are fibreglas, and they can REALLY generate noise when
moving down the road through dry and/or dusty air. I could hear them as they passed my truck. Friend K0RZ built a small (3") tuned "sniffer" loop for 20M that was VERY helpful in tracing and pinpointing noise sources.
Noise Abatement  
by K4IA on February 27, 2003 Mail this to a friend!
Great ideas but don't forget the greatest noise fighter of all - the ClearSpeech DSP speaker. It takes care of noise from the "other guy," power lines, etc. as well as your own noise. I wouldn't operate mobile without mine.
RE: Noise Abatement  
by N2KEJ on February 27, 2003 Mail this to a friend!
Does anyone know if the clear speech DSP speaker improves reception on FM (6 meters)?

Steve N2KEJ
Noise Abatement  
by WB2GFR on February 27, 2003 Mail this to a friend!
Good article. I have to add one more item, stuff wife in trunk, make sure you have a remote trunk release. 73 s John
RE: Noise Abatement  
by VE6XX on February 28, 2003 Mail this to a friend!
Greetings All: K0PP, Sir: Glad to know you are still alive Ken, long time no see, hear, or talk. How are things in the "Treasure State" ? I echo your sentiments regarding the problems with fibreglass worse thing to the radiation from a Radio Shack radar detector! To the gentleman who asked about the "clearspeech" unit on six metres......The clearspeech provides a measure of noise reduction on any radio &/or band/mode I have tried. I personally would not operate HF mobile without one. The six metre noise problem is severe in some areas, & the "clearspeech" will clean up most of what the limiters in the FM receiver don't. Interestingly, the most effective FM noise blanker for the six metre band was offered by Motorola in a number of their "Low Band" FM mobiles, & was referred to by Motorola as an "extender". It worked by sampling the RF in the receiver , routing the receiver RF signal through a delay line & feeding back the processed noise pulse to "punch holes" in the signal where the noise pulse occurred, thereby effectively removing it!
It worked better than any system I have ever encountered. Since the "clearspeech" is an audio DSP unit it sees only noise associated with the receive audio & should clean up a lot of the "crud" experienced on six. Alan: Thanks for your reply. A stainless steel exhaust would certainly have some advantages over the standard steel pipes but cost isn't one of them! Your technique for installing the bonds makes technical sense & I'll bet it works just fine. For the gentleman who asked about the static discharge wicks & whether or not they dragged on the ground.....The wicks work much like the lightning rods on a building. The wicks have a low Z connection to the vehicle, & the "tail" of the wick has numerous small diameter strands that "bleed" the static potential off the vehicle as it builds. In other words, it prevents the structure to which it is attached from accumulating a prejudicial static potential. It couples the "charge" to air molecules in the slipstream in which it resides. Think of them as spillways on a dam that allow excess water to flow through them to the downstream side of the dam instead of raising the upstream water level to the point that it overflows the dam. Lightning rods constantly "bleed" accumulating charges on a structure to ground, thereby reducing the potential between the structure & the cloud charge, & with it , the likelihood of a strike. Same idea with the static discharge wicks...the charge is continuously dissipated to the slipstream, instead of building up until there is the potential discharge "spark", actually a series of sparks as the potential builds & discharges over & over again, giving us the sputtering whine we hear in our receivers. Alan, your treatise has once again inspired a host of positive comments, we look forward to having you share your knowledge & experience with us on a regular basis. Thank you once again.
Noise Abatement  
by KC4EOE on March 1, 2003 Mail this to a friend!
Thanks, Alan. Since most of my hamming is done from the mobile, I cannot wait to get started adding the fixes to work out some of those noise gremlins in my vehicle. I need to find a source for low-cost torroids though, since the local Radio Shack wants to be included in my will for the price of theirs. They must think their snap-on model is made of rare metal. I like the slipstream static rod idea. I have noticed that particular noise as I increase my speed and have never been able to identify it until you spoke of it. 73's and keep those good ideas coming.
RE: Noise Abatement  
by AC6DN on April 16, 2003 Mail this to a friend!
I use OX-GARD on all connections especially grounds, and especially ones with dissimilar metals (Available in hardware stores in the electrical dept. (for aluminum to copper connections).
If the ground connection is hot like an exhaust pipe, I use anti-sez (SP?). I first sand till I see, clean metal. Then I drowned the braid, pipe (& clamp) in the anti-sez, then I use the SS house clamp.
Ive never had a connection go bad , yet (from corrosion)
Bruce AC6DN
1.8-1300 MHz, 14 antennas, all mode, mobile
RE: Noise Abatement  
by AC6DN on April 16, 2003 Mail this to a friend!
Yah, I had a Icom IC-706-0, It was a noise receiver not a HF mobile radio
I have a Yeasu FT-100d, now...
Bruce AC6DN
1.8-1300 MHz, 14 antennas, all mode, mobile
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