By Russ Edmunds
So you say you've got a noise problem? Doesn't pretty much everybody these days - at least among the BCB DX fraternity? In an age of a dizzying number of electrical devices, we find that more and more of them cause interference on the AM band.
As we continue this discussion, we'll talk about many of them, as well as discuss some tips for finding and dealing with them. The first step is to determine what kind of noise is present. Is it constant or intermittent? If it's intermittent, does it seem to have a regular pattern or is it random? Does the noise affect only a portion of the band? If you use a loop antenna, can the noise be nulled? Is the noise present only at night, or at twilight? These are the types of questions to answer first.
If the noise is intermittent, then something is creating it only sometimes, and the pattern or lack of it may give you hints. For instance anything with an electric thermostat, whether it's an aquarium heater, a clothes dryer, a stove, an electric blanket or any number of other items, you'll hear either a short popping, buzzing or crackling sound, followed by silence until the thermostat is called to action again. If you hear a very regular periodic buzz, it may be a motor that needs to be serviced, likely for bad brushes. This motor could be in a refrigerator or a washer or dryer, a furnace or a power tool. If the noise appears at different frequencies throughout the band, and is constant sometimes and absent other times, it may be TVI (television interference). A noise which is usually only present at night, twilight or on very dark days can usually be traced to some sort of a light sensor for automatically turning on indoor or outdoor lights or other appliances.
So once we think that we have an idea as to what type of noise we may be dealing with, the next step is to try to locate it. There are two basic ways to do that, and each requires the use of a hand-held battery-powered AM radio. Of course, if you have a non-constant noise, you'll need to do this when the noise is in evidence.
First, let's determine whether you have a situation where the noise is prevalent on the receiving gear in your shack, but not on the portable radio. This may be due to a problem in your receiver or in your antenna. If you're using a loop, it is easy enough to physically put the portable inside the field of the loop. If there now is noise on the portable, the noise is being picked up by the high gain of the loop antenna, and it is probably nullable to determine a direction for the external noise source. If that is the case, you'll need to follow the procedures further below for noises produced outside of the building you DX from. If there is still no noise on the portable, then there is likely a problem with your receiver. The best bets are poor grounds, bad capacitors to ground or possibly bad tubes. In this case a complete check of the receiver is called for. If you're using an outdoor antenna, it is possible that the noise is being received by the antenna just as if it were a radio signal. In the case of very long and/or highly directional antennas, this is often a situation where the noise source may not be close enough for you to easily identify it.
Once the receiving system is eliminated as the source of the noise, take the portable radio with you to the electrical panel in your residence, turn it on and hold it near the panel. Then turn circuits off, and then back on again, one by one. As you turn each one off, listen for the noise to disappear and to reappear when you turn it on. If that occurs, you know that the problem is on that circuit. If that doesn't seem to work, repeat the process, except omit turning each circuit back on until you've turned them all off. This may determine that you have two noise-producers on two separate circuits. After all of this, it's very possible that either the noise remains even with all circuits off, or that it only disappears when the mains are off. If the latter, try to reposition the portable radio so that it's right next to the main power cable coming into the panel. If the noise reappears, or if it never disappeared, then it's probable that it's being transmitted along the power lines from an external source. If you've been able to isolate a spec ific circuit, and you know what rooms are on that line, refer to Chart I at the end of this article for probable noise generators.
If your investigations at the electrical panel don't turn up any leads, take the portable radio with you, leaving the circuits turned off, and locate places where other electricity-based services such as cable TV or telephone, enter the building. Place the portable radio near the wires for these services to see if the noise becomes louder as you do so. If so, try to compare the loudness of the noise here as opposed to at the electrical panel to determine which is the more likely carrier of the noise. Then return to the electrical panel and turn the power back on to all circuits. Next take the portable radio again, and go outside see if you can identify any external sources for the noise. Check at nearby utility poles, if your electricity is furnished above ground. After securing permission to do so, take the portable and walk around any buildings on adjacent properties, trying to compare noise levels there against both each other and at your residence. If you find that one particular neighboring structure seems to have the loudest noise, you'll need to get permission to perform the same checks with the utilities that you did at home. In many cases where the noise is externally generated, it may be coming from a neighboring building.
Once you've located a particular area where the noise is originating, it's time to check for the specific source. This can also be done using the same portable radio, although it's often useful to think about a target list of the types of things that are most likely to cause electrical noises. For a preliminary list, refer to Chart I at the end of this text. Depending on what device is the culprit, you may have some options for correcting or at least reducing the noise problem. Unfortunately, even some sources of problems in your own living quarters may not be so easy to fix, and those which are external may be even harder, assuming that you're able to identify them at all.
Sometimes you can eliminate or reduce noise generated through the power lines by making sure that your receiver is on a separate circuit from any noise-producing devices. Another may be a noise-reducing line filter. In some cases, where the noise isn't generated by something which absolutely must be running while you're DX'ing, you can simply turn the noise source off. If your outdoor antenna is picking up noise radiated through the air, a noise-reducing antenna may be the answer. Perhaps even relocating an outdoor antenna to place it further away from a known noise source will be adequate. If you have strong reason to suspect that the noise source is external, whether you believe that it is being generated by faulty power generating equipment or whether you believe that it is simply being radiated over the power lines, most electric utilities (as well as most telephone and cable TV companies) have people on their staff who specialize in investigating electrical noise complaints or problems, and you should make use of these persons where appropriate. A local amateur radio club may also have a member who has become an expert in tracking down noise problems.
If you have narrowed your focus down to a particular electrical device, you should be aware that although the device itself or the literature supplied with it may state that it is "FCC Type Accepted", this might not mean very much. Any item which may either cause or be susceptible to radio interference must meet FCC requirements. Generally speaking, the FCC requires that any such item not create interference above certain specified parameters, but very often the result is that some level of interference within some close proximity to the device in question is permissible. The intent is that your appliances don't interfere with your neighbor's radios and the reverse, although in some cases that may still be permissible. Remember that we are practitioners of a hobby most people have never heard of, and that government regulations aren't intended to necessarily protect against noise which prevents us from hearing distant stations nor are they intended to always protect against noises generated within our own residence from interfering with radios in that same residence.
In summary, here are a few added observations about noise and noise-reduction. Generally, a loop antenna will pick up less noise than a random wire antenna, a vertical antenna will usually pick up more noise than a horizontal one, and a directional outdoor antenna array will generally exhibit the same reception pattern for externally radiated noises as they do for radio signals. If you have multiple outdoor antennas, it may be possible to use a phasing unit to mix the signals from each to reduce specific noises, and if you do not, it may be worthwhile to investigate adding even a simple one just for that purpose. Also, some power line-transmitted noise can be eliminated or reduced through the use of a battery-powered receiver located as far as possible from any power lines.
|Noise Source||Type of Noise|
|Fluorescent fixtures||Continuous rough sounding buzz|
|Halogen bulbs||Continuous buzz|
|Electronic light dimmer||Continuous often slightly wavering buzz|
|Photoelectric sensor switch||Continuous often slightly wavering buzz (SCR or Triac type)|
|Oven, clothes dryer, etc.||Periodic crackling or short-burst buzz electric pilot|
|Aquarium thermostat||Periodic crackling or short-burst buzz or popping sound|
|Electric garage door opener||Steady low-frequency (usually < 1 kHz.) hum or buzz photocells|
|Television||Continuous but often-variable rough- sounding buzz|
|Computer||Monitor can sound like TVI; computer itself can emit various buzzes at differing frequencies|
|Power tools||Popping noises, sudden noise pulses, or buzzes|
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