Noise Identification
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Contents: Intro; About the Noise; Ignition Noise; Fuel Pump Noise; Electric Motor Noise; Alternator Noise; Combinations; Electric Trailer Brakes; Noise From Others; Conclusion;
The toughest obstacle a mobile amateur radio operator has to face, is attenuating the various undesired noises emanating from our transceiver's speaker. By noise, I mean all of the various forms of RFI, EMP, and AFI, whether it be induced, inducted, or received.
The first place to start is my Wiring article. If you don't take the necessary time to wire your installation correctly, finding and curing a noise problem becomes much more difficult. For example, ground loops are the primary cause of alternator whine, not the alternator! In short, if you're using existing wiring, all bets are off!
Bonding is the second most important item in minimizing any form of noise. For example, the primary cause of excessive ignition noise is failure to properly bond the exhaust system. And one strap is never enough!
Another major consideration is proper Antenna Mounting. Excessive ground losses reduce the strength of the received signal, which in turn reduces the signal to noise ratio. Although more commonly associated with FM radios, SINAD (20 log [signal + noise + distortion/noise + distortion]) is the measure of how well you're receiving an incoming signal. As you can see from the formula, too much noise and you can't hear well enough to carry on a conversation.
Here are some additional resources: Noise Abatement; Another Look at Noise Abatement, and Beads. If you've read these articles, you know that reducing received noise is a multi-front war which requires a coordinated attack. One of the more important aspects of the war is identifying the enemy, and that is what this article is about.
This article contains several sound files which were recorded on an Olympus® digital recorder. They were transferred into Sound Studio® where the recorder's clicks and beeps were edited out. The files were resampled at 11.025 kHz to reduce download time, and saved as AIFF (Audio Interchange File Format) and thus compatible with Macs and PCs. I did my best to record these at a high level, but it may be necessary for you to turn up the output audio on your computer. The sound files open in a new window where you can play them as many times as you wish.
I use the term noise in a very general way in this article. The actual noise we hear can be audio spectrum noise, or a result of RFI, EMI, and EPI, or a combination of any or all. This obviously makes identification difficult. So what follows is a small sample of what you might encounter in any one specific vehicle, but certainly not all. While I'm on the subject of vehicles here's an advisory or two.
First, two otherwise identical vehicles may have vastly different noise levels. If I knew why this was so, I'd be on my way to being rich! Secondly, there are some vehicles which just can't be made quiet, at least not as quiet as you and I would like. In general, however, if you have to use your noise blanker you haven't done enough. Either that or you have one of those vehicles made where the rivers Styx and Charon cross.
The most prevalent sound we have to deal with is ignition noise. The biggest problem is, it can sound similar to injector noise or shuttle noise in a diesel (see second paragraph below). In some cases, the noise pulses from both the injectors and ignition systems interact and the noise appears more of a hash than what you're about to hear. Ignition Noise Nonetheless, if you listen carefully you'll actually hear the two pulses which are very close together. The lighter pulses are from the injectors, and the heavy pulses are from the ignition. This is a very good example of a compound noise which makes identification and abatement difficult at best.
With the exception of the Gen III push rod engines in GM products, and a few older legacy models, all automobile manufacturers have abandoned the use of plug wires all together, and switched to COP (Coil Over Plug) technology. This technology combines the coil, plug, and sometimes the switching circuitry all into one neat package. The left photo shows what they look like. Note the split bead over the control cabling. On all Ford products which use COP technology (and other too I suspect), there is an internal ferrite bead which may (emphasis on may) make the external ones unnecessary.
On the forefront is yet another gasoline engine technology which combines a combustion chamber fuel injector, the spark plug (igniter as it is now called), a coil pack, knock sensor, and electronic controls all in one package. Some 2006 models are already equipped with them with more to come. While this new technology answers the mandated pollution requirements, it appears to make our noise abatement ever more difficult. For example, the fuel rail pressure on some models is almost 1,500 psi! This high pressure requires higher current injectors, just like their electronic diesel counterparts.
Fact is the latest diesels from Mercedes, BMW, and Volkswagon (perhaps others as well) use a new Bosch electronic fuel injection system. The jury is still out with respect to abating the generated RFI from these new units.
Here's a bit of trivia. A few years back, a company named Esslinger Engineering designed and built an electronic valve actuation system. It used rather large electromagnetic coils to both open and close the valves rather than use a cam shaft. In theory this would allow minute control over valve lift and duration; an engine design engineer's utopia. They actually had several systems installed on Ford's ubiquitous 2.3L 4 cylinder engine. Although it worked well, one of the stumbling blocks was the huge amount of RFI generated by the system.
Another common noise is caused by electronic fuel pumps. Most are mounted inside the fuel tank, but a few are mounted on the frame rail. Some high performance vehicles have both kinds, and some trucks have two or more. The one you're about to hear is a tank mounted one. You'll notice a slight delay after the ignition is turned on, then you hear the pump charging, and then a rhythmic pulse as the pump maintains fuel rail pressure. Fuel pump Noise The engine was not running. Had it been, the pulses would be much closer together.
Every modern vehicle on the road has at least five or six electric motors, and some with as many as 50! Engine cooling fans, AC fans, IAC (Idle Air Control) motors, power seats and window motors, some cruise controls, remote controlled mirrors, power door locks, and the list is almost endless. When any of them operate they create hash, spikes, and/or pops in our received audio. Most of them sound similar albeit some are steady like AC fans, and some are intermittent like IAC motors. The noise you're about to hear is an AC fan which is being turned on and off to make it easier to identify. I did this because the hash you hear is very similar to atmospheric noise leading some folks to believe it is. Electric Motor You can imagine the difficulty of identifying just one motor when several are running at the same time. The ones you really have to worry about are the first three I listed in this paragraph, and the throttle position motor if your vehicle is drive-by-wire equipped.
There is a trend in the industry to switch over to brushless DC motors. Believe it or not, this is being done to reduce RFI (it's about time something is being done at the manufacturing level!), and increase mechanical life. In some applications, linear actuators are replacing rotating motors for the same reasons. Let's hope our perceived level of vehicle noise goes down, not up!
The following information assumes there is indeed a bad diode array. Nowadays, it is very rare to have a diode fail, but it does happen. This said, in almost every case of alternator whine I have been involved with in the last several years, was a result of a ground loop. And in those cases, all but one utilized a mag mounted antenna. Here's more food for thought.
Alternator whine is not as prevalent as it once was due in part to better designs and much better diode arrays. For some reason, GM products seem to be the worse for this malady, with older model Toyotas coming in second place. Getting dealers to repair units under warranty is difficult at best. If the alternator puts out the correct voltage and current, their obligation is over. And replacing the diode pack or the complete alternator is not a guaranteed cure as some replacements, new and rebuilt, are just as bad if not worse than the original. Alternator Noise I recorded this on a second receiver as the whine was impressed on the transmit signal, but not on the received signal. This is a common occurrence as most transceiver finals are hooked directly to the incoming power, where as the receiver usually has some DC supply filtering. This is not always the case, however. If you listen carefully you'll hear the IAC motor pulsing in the background.
Some alternators pulse the stator current similar to a switching power supply, while the others (usually older models) use an analog method like a linear power supply. Similar to a switched bench supply, the frequency and/or the pulse width may be varied (independently or together). The RFI from these models sounds like the old cartoon rat-a-tat-tat used for machine gun sounds. Although it may sweep across the bandpass, that is not always the case. If you're plagued with this particular noise, the alternator is a good place to start looking. Unfortunately, I don't have a recorded example of this form of RFI. If you do, I'd like to hear from you.
Hybrid vehicle present a new level of sophistication especially with respect to alternators. A lot of hybrid units replace the alternator and the starter motor with just one big unit. Although my brother did well operating mobile in his Toyota Prius, the jury is still out on the majority of these new systems. We'd better get used to them, however, as they are the vehicles of the future even for trucks and SUVs of all types.
The above examples are by no means the only noises present in modern vehicles, nor are they isolated as they are here. Fact is, most of the time you can hear several at once. Combination This is why it is so important to do the obvious bonding and beading first before trying to fix the remaining maladies.
There is one key word every reader should take to heart - perseverance. I fought one noise problem in my Acura for nearly a year before I found and corrected the problem. I'm still plagued with an RFI ingress problem with the traction control system on 17 meters, but sooner or later I'll fix that too. In short, it takes time to run down noise, and sometimes it takes a lot of work to abate it.