A Communicator Reprise: September 2011
At one of our Friday breakfast meetings a conversation came up about how some of us have such a high noise level, a great many signals are lost in that noise. Depending on the frequency or band you listen to, some are experiencing 20db above S9 as their noise floor.... Me? I have to deal with a S7 to S9 noise floor on 80 metres, and a S3-S5 on other bands.
When I started looking into this topic, I was overwhelmed by the books, articles and white papers on the subject. There is a lot of information on both EMI [Electromagnetic Interference] and RFI [Radio Frequency Interference]. A new term has come into popular use which seems to mix the two into EMC [ElectroMagnetic Compatibility] which is the characteristic of any or all electronic devices to either not emit unwanted signals, and/or not be influenced or interfered with by other devices.
In Ham speak, we can simplify these terms by stating that RFI is interference caused by YOUR station equipment getting into other devices, from TVs, to electronic organs, to your touch controlled paper shredder. EMI is interference FROM other electronic devices which cause your receiver noise floor to rise. OK, not entirely technically correct, but it serves my purpose here, we can debate later.
As our lives become filled with technology, the likelihood of electronic interference increases. Every lamp dimmer, garage-door opener or other new technical “toy” contributes to the electrical noise around us. Many of these devices also “listen” to that growing noise and may react unpredictably to their electronic neighbours. Whether it’s called EMI, RFI or TVI [Television Interference], unwanted interaction between intentional and unintentional receivers and transmitters has stimulated vigorous growth in the field of electromagnetic compatibility (EMC).
The scope of EMC includes all the ways in which electronic devices interact with each other and their environment. The primary aspect of EMC that concerns amateurs is interference to or from Amateur Radio communications. Sooner or later, nearly every Amateur Radio operator will have a problem with interference, but temper your dismay. Most cases of interference can be cured!
Since this is a huge subject to deal with, I will cover only the topic of reducing EMI INTO your receiver. In other words, what can you do to reduce [notice I didn’t say “eliminate”] that S9 noise floor so you can hear the QRP or DX stations… or anyone for that matter.
All cases of EMI involve a source of electromagnetic energy, a device that responds to this electromagnetic energy (victim) and a transmission path that allows energy to flow from the source to the victim. Sources include radio transmitters, receiver local oscillators, computing devices, electrical noise, lightning and other natural sources. There are three ways that EMI can travel from the source to the victim: radiation, conduction and induction. Radiated EMI propagates by electromagnetic radiation from the source, through space to the victim. A conducted signal travels over wires connected to the source and the victim. Induction occurs when two circuits are magnetically (and in some cases, electrically) coupled. Most EMI occurs via conduction, or some combination of radiation and conduction. For example, a signal is radiated by the source and picked up by a conductor attached to the victim (or directly by the victim’s circuitry) and is then conducted into the victim. EMI from induction is rare.
Look Around — Aside from the brain, the eyes are a trouble shooter’s best tool. Look around. Installation defects contribute to many EMI problems. Look for loose connections, shield breaks in a cable-TV installation or corroded contacts in a telephone installation. Fix these first.
Problems that occur only on harmonics of the fundamental signal usually indicate the transmitter. Harmonics can also be generated in nearby semiconductors, such as an un-powered VHF receiver left connected to an antenna, or a corroded connection in a tower guy wire. Harmonics can also be generated in the front-end components of the TV or radio experiencing interference. Is the wiring connected to the victim equipment resonant on one or more amateur bands? If so, a common-mode choke placed at the middle of the wiring may be an easy cure.
These are only a few of the questions you might need to ask yourself. As we discover what devices cause EMI, let’s delve into types of EMI ‘noise.’ First, it is worth keeping a log of exactly when the EMI occurs as this can give a clue to the possible source. Tuning across the affected band or bands can also give some clues about the source of the interference which normally falls into one of the following categories:
Narrow band interference affects one or more spot frequencies in a band with little or no detectable interference in between these frequencies. On an SSB receiver, a true narrow band source would be heard as a tone, possibly rather rough but narrow enough to be reduced by means of a notch filter.
Broad Band with no peaks
If interference appears right across a band at about the same level with no peaks, it is classed as a broad band source.
Broad band with broad peaks
Some sources such as switch‐mode power supplies and digital electronics produce broad band emissions with regularly spaced broad peaks. The spacing between the peaks indicates the fundamental frequency. The peaks may not be well defined so it is best to note the frequencies of 11 regularly spaced peaks and divide the difference between the highest and lowest by 10.
Broad band with narrow peaks
Some emissions are broad band but also contain narrow band signals as described above. This is characteristic of digital electronic circuitry.
The frequency of a narrow band emission may drift due to temperature changes. The times of these temperature changes can give some clues about the source. If it is crystal controlled, the drift may be very slight but if it uses a ceramic resonator, it may drift up to a few kHz at VHF or a few hundred Hz at HF.
It is worth listening to the interference using FM, SSB and AM modes if possible. You may find one of the following characteristics:
This may be a harmonic from a crystal oscillator.
60 or 120 Cycle [Hertz] buzz.
If the audio signal is viewed on an oscilloscope triggered on 'line', the trace stands perfectly still if the interference is synchronized to Hydro’s 60 Hz.
A steady hiss like the background noise level on the band but at a considerably higher level.
Some sources are modulated with a characteristic sound (see below).
Some residential sources of EMI
The line time base frequency of 625 line television systems is 15.625kHz. Harmonics may be heard as narrow band signals on multiples of this frequency, for example, 3500 kHz, 3515.625kHz, 3531.25kHz, etc. As the line frequency is 1MHz divided by 64, harmonics are found on multiples of 125kHz. If the TV is receiving an off‐air program, the harmonic will usually have a sound which changes with picture content when heard on an SSB or CW receiver. To prove that a TV set is the source, try watching another TV set (with low EMI!) and select different channels until you find one where changes in the picture coincide with changes in the sound heard on the radio.
Some large screen plasma TV sets radiate broadband interference mainly in the lower half of the HF band. Because of the large screen area most of the interference comes directly from the screen. Measures such as a mains filters are unlikely to be effective. Fortunately, so far as TV sets, are concerned “plasma” is an obsolete technique so incidences as interference should reduce as equipment is replaced.
Switch‐mode power supplies
A switch‐mode power supply (SMPS) generates a square wave at a frequency of 30 ‐ 90kHz or more. On the LF, MF and lower HF bands, harmonics from an SMPS can produce broad band EMI with broad peaks and 100Hz modulation. The peaks are spaced at multiples of the switching frequency. On the higher HF bands and at VHF, the peaks may merge together.
TV power supplies
When heard on an AM or SSB receiver, the sound form a TV switch‐mode power supply usually changes with picture content (see also TV line time base harmonics above) but is broad band and may peak at a certain frequency such as 14‐18 MHz. The switch mode power supply also runs when in standby mode and its characteristics may change so that interference is only noticeable in standby mode. Emissions in standby mode are normally continuous but in some sets sold since 1999, the noise is modulated at about 8 ‐ 10Hz in standby mode. This produces a 'chuff‐chuff' noise like a fast steam train. With old Analogue TVs being discarded over the next few years, be prepared for new problems with digital TV.
TV 'set‐top boxes' – the Shaw, Telus, Satellite Boxes & PVR
There are various types of TV 'set‐top box' for satellite TV, cable TV, digital terrestrial TV or video on demand via ADSL (Asymmetric Digital Subscriber Line). These normally have switch‐mode power supplies that run continuously.
If the EMI occurs mainly after dark, does it appear when a certain light or lights are on in a room nearby?
For lighting which uses 12 volt halogen spotlights, the transformers may either be a conventional type or an 'electronic transformer' which is a switch‐mode power supply with AC output.
Compact fluorescent and LED lamps (Low energy lamps)
Most types, are electronic and contain a small switch mode power supply. There are also larger non-electronic types such as the Philips SL range which generate less EMI but have a heavy iron‐cored choke.
Computer power supplies
In a desktop computer, the SMPS is normally in a screened box with a mains filter and may therefore produce much less EMI than a computer monitor where the SMPS may be unscreened. Laptop computers have an external AC power supply unit/charger which is normally an SMPS without screening.
The power supply runs 24 hours a day and it almost always a switch‐mode type.
EMI from an AC or DC electric motor with brushes and a commutator is broad band without peaks. Its pitch varies as the motor speed varies. The variations in speed and the pattern of use can give clues about the source. For example, this might be a washing machine or drier, sewing machine, electric lawn mower, food mixer, electric drill, hair dryer or even a model railway. It is not likely to be a refrigerator as these normally use induction motors which do not produce EMI.
Faulty thermostats can arc for 1 ‐ 30 seconds or more producing broad band EMI with no peaks and 100Hz modulation. This may be heard on a number of HF and/or VHF bands. The most common source is a faulty gas central heating boiler thermostat and it is likely to be worse in winter. The arcing may occur at every 5 ‐ 20 minutes although in some cases it could be as often as two or three times per minute.
Conventional fluorescent lights
EMI from fluorescent lights is broad band with no peaks and is modulated with a 120Hz buzz, mainly on the LF, MF and lower HF bands. Fluorescent lights have been required to include EMI suppression since 1978 although most met the relevant standard long before this date. If the tube is worn out and flickering at 60Hz, this can increase the level of EMI.
EMI from dimmer switches is similar to that produced by fluorescent lights and is stronger when the lamp is dimmed than when on full brightness. Dimmer switches sold in the Canada have been required to include EMI suppression since 1978 although most met the relevant standard long before this date. They seldom cause problems to amateur reception unless they are faulty or are a type not designed for the Canadian market – hint hint eBay buyers of Chinese products.
Various oscillators in a computer and its associated components such as the keyboard and mouse can produce narrow band radiated emissions. Some are crystal controlled and generally have no drift or modulation while others use a ceramic resonator which drifts and may have slight frequency modulation which can be heard as a 'warbling' noise on an SSB or CW receiver. Such modulation may sound like someone typing on a keyboard or playing a game. Almost all PCs have a crystal oscillator at or near 14.318MHz although this signal may not be particularly strong. Nevertheless, if it is present at the same time as other signals, this shows that the other signals are likely to come from a computer. In many cases, a computer monitor radiates more EMI than the computer itself. In addition to broad band emissions from the SMPS in a computer monitor, there may be line time base harmonics which are similar to TV line time base harmonics except that the spacing is larger (31 kHz or more). There are numerous different line frequencies depending on the screen resolution and refresh rate. Computer line time base harmonics normally give a very pure crystal‐controlled note and are likely to be strongest on the 1.8 and 3.5MHz bands.
Intruder alarm systems
Intruder alarm systems normally contain a microprocessor and can radiate signals from the wiring to the sensors on the HF and/or VHF bands. As they normally use a ceramic resonator, the harmonics drift slightly and may have slight modulation which can be heard on an SSB receiver. This modulation may change if the alarm ever goes off and may also change when the user presses keys on the control panel.
Other digital electronic devices
Digital electronic circuitry can radiate narrow band signals on certain frequencies such as harmonics of the clock frequency and may also produce broad band signals. Such sources include NICAM decoders and other digital electronics in TV sets, video recorders and satellite receivers/decoders. Many of these devices are connected to long cables which can radiate EMI on HF bands as well as VHF.
Many modern cable television systems use vision carriers from 128MHz upwards on multiples of 8MHz up through the 2 metre Ham band. The street cabinets normally contain a switch‐mode power supply which may produce detectable emissions on the HF bands due to common‐mode signals conducted along the coaxial cables.
Fax machines contain a microprocessor which runs continuously. If a computer is connected to a modem, this can allow EMI from the computer to be radiated via the telephone line. If the modem can receive fax or voice calls, the owner may leave the computer running all the time. If a telephone subscriber has an ISDN (Integrated Services Digital Network) line, the line carries 90V DC which powers a switch‐mode power supply in the customer's premises. Some types of ISDN equipment at the customer's premises can produce EMI when a call is in progress. Businesses and even some homes may have their own internal telephone exchange or PABX. Some types can produce EMI on the HF and VHF bands.
Emissions from overhead telephone lines
If the EMI is strongest under telephone lines or close to a telephone pole, the source could be one of the items mentioned above but in many cases, it is something completely unrelated to the telephone system. If anything feeds EMI onto the AC in a house, this can be coupled onto telephone wires via the AC transformer of any Hydro powered telephone equipment such as an answering machine or a cordless phone.
Vehicles - Ignition systems
Although there have been regulations controlling ignition interference since 1952, this can be a problem for weak signal reception near a busy road. Many transceivers contain a noise blanker which is effective against the short impulses from vehicle ignition systems.
Remote keyless entry receivers
Some cars made since mid 1994 use radio keys operating on 433.92MHz. Radio key receivers in some cars contain a local oscillator which runs continuously somewhere in the range 433.275 ‐ 433.475MHz. Other types use a super‐regenerative receiver and some aftermarket alarms sold in 1994 and 1995 can emit broad band noise across the 430‐440MHz band
These are table lamps with a touch‐operated switch which turns the lamp on and off and selects several levels of brightness. They contain a sawtooth oscillator which operates continuously and produce emissions which are similar to an SMPS but with a fundamental frequency of around 190kHz. Some models sold before 1996 contain no EMI suppression.
Garage door openers
The super‐regenerative receivers for some 173MHz remote‐controlled garage door openers manufactured in the late 1980s radiate broad band noise on 430‐440MHz. They can also receive VHF radio paging and rebroadcast it at a number of frequencies on the 430‐440 MHz band!
Electronic water conditioners are claimed to reduce deposition of lime scale. Some types such as the "Water King" and "Water Imp" use a sequence of audio frequency tones which have harmonics up to 28MHz in some cases. The radiated emissions have a very unusual characteristic as the a tone changes about once a second in a sequence which repeats every few minutes.
EMI from an electric fence is a regular clicking noise. The source is likely to be a sparking at a faulty insulator rather than the electric fence unit itself. Try looking for flashovers in the dark (with the landowner's permission).
Overhead power cables
Overhead power cables can radiate broad band noise with 120Hz modulation. High voltage cables always produce a certain amount of EMI due to corona discharge from the cable itself but EMI can be greatly increased due to arcing at a faulty insulator, in which case, the level of EMI may reduce in dry weather.
This sounds rather like packet radio but usually starts with a tone. Strong signals from nearby radio paging transmitters may be heard on the 2 metre band or other bands but in most cases, such breakthrough is caused by shortcomings in the amateur receiver. Transceivers with extended receive coverage are more likely to be affected than those which only cover amateur bands. Hand‐held transceivers connected to an outdoor aerial can be particularly susceptible.
Power line Adaptors (PLAs)
In recent years these have become a serious source of interference. They are sometimes used for networking computers but the most common use is for video distribution. Generally they minimize emissions in the amateur bands (known as notching) so that interference is most likely to be noticed on the HF broadcast bands.
Your Cell Phone
My phone’s Bluetooth makes a strange rhythmic buzz in one pair of my computer speakers when it communicates with its companion Bluetooth device. Took me days to figure that out, but just one pair, not any other in my ham shack? Cheapest solution was to turn the cell phone off!
Searching for the Source
Basically, the first step is to determine if the noise is household noise or neighbourhood noise or atmospheric noise; the latter we can't do much about except put up high-gain, highly directional arrays to increase your signal to noise ratio.
- Start out by recording the noise floor on 80 & 20 meters, either via the S-meter or panadaptor.
- Put a 12 volt car battery across the terminals of your power supply, fully charged of course.
- Then turn on everything in the house and I mean everything. Best to do this test with the family away for 2-3 hours. Record the result.
Turn off all the circuit breakers so there is no AC coming into the house… the only thing on in your house should be your transceiver, powered by the battery. If the noise goes away, it must be household generated (duh). Turn the volume up [if you don't have help] and turn on one circuit breaker at a time until the noise returns, then on the breaker that causes the highest return of the noise floor. The next step is to turn off all the others you've turned on so far, then locate what is still on in the house and one-by-one turn it off [or unplug it], until the noise goes away, and hopefully you have located the RF noisy device or devices, before the fridge defrosts. You may need to repeat this to find multiple sources of noise.
Again, look for noise sources in Ryobi battery chargers, Plasma TV's, switching power supplies, electric blankets, electronic bug zappers, electric fences, cell phone chargers, cordless phone chargers, electronic exercise equipment, air ionizers or conditioners, electronic light dimmers, timers, readouts that are multiplexed [scanned], computers made between 2000 and 2007 as the CPU oscillated at some direct or harmonic frequency on various ham bands. One of my main computers generates birdies all up and down the 75/80 meter band – about 3 ‘S’ units of buzzes, clicks and tweeting birdies! Any computer that doesn't run in the GHz. range is a potential source of HF noise.
Don’t rule out your hot tub motors, timers and heaters too… pumps for the pool and especially as the starter capacitor ages, fridges and freezer with induction motors shouldn’t be an issue, but don’t rule them out. Run the microwave oven too… they leak no matter how good it is… and the older the unit, the more it leaks RF. We know some florescent fixtures can be noisy, even some of the new energy efficient ones.. they can be the worst offenders and, don't forget the toxic mercury-filled "eco-bulb” we are almost forced to use.
Check the house ground rod connection, and any device that has a ground connection. Don't just tighten, take it off, burnish it, add some anti corrosion compound and re-attach.
Sodium & Mercury Street lights, their ballast noise, Shaw cable boxes not properly grounded (they use the 2 metre ham band as a signal carrier) If it's not grounded properly or the box is left open, your RF signal interferes with cable and vice versa (in VHF).
Including electric fences, electronic pet barriers, solar panel inverters are very RF dirty. Only one or two of the more expensive ones are RF suppressed, all others radiate like an unprotected spark-gap transmitter!
Bad Pole Insulators
And old pole transformers (or loose connections as Fred VE7IO was telling us about at breakfast that morning.) Just about any motor with brushes and spark plugs.
On the HF bands, interference can enter your home via the AC [Hydro] supply whether underground or overhead and can be radiated by your wiring. In such cases, switching off a double pole main switch at the fuse box will probably reduce it, although this depends on the exact layout of your Hydro wiring. Pickup of AC‐borne interference on the HF bands can often be reduced by moving your aerial further from the AC wiring [if possible], or by using a balanced aerial such as a dipole instead of an end‐fed aerial. Aerial and Antenna – the same thing.
If it is not in your own home, the next step is to go out and search for it using a portable transceiver or receiver, or get someone to help you if you are unable to do this yourself.
In the case of HF Hydro borne interference, the source is likely to be on the same phase as your own main supply. In a street of houses, every third house is normally on the same phase. On VHF, if you have an aerial on a rotator then it should be possible to get some indication of the direction of the source. EMI which occurs continuously or frequently can often be located without a directional aerial, simply by going around searching for the strongest signal.
For EMI which only occurs intermittently such as an arcing thermostat, a portable directional aerial is very useful. In either case, the receiver should have an 'S' meter, preferably a moving coil type. It is also useful to have an attenuator to reduce the sensitivity when you get closer to the source.
One possible problem is that EMI which is quite strong when using your main station aerial cannot be heard at ground level on a portable receiver. For a narrow band source, the maximum sensitivity is achieved by using CW mode with the narrowest possible bandwidth such as 500 Hz. For broad band sources such as arcing, greater sensitivity is achieved by using a receiver with the widest possible bandwidth. The first thing to establish is whether the source of the EMI source is nearby (within about one hundred metres for example) or further afield such as the next street or even the next town. Getting someone to drive you around the local roads in a car with a portable receiver connected to the car aerial may show a clear peak at a certain point which is not apparent when walking. If interference is being conducted along telephone wiring or Hydro wiring, there may be a number of peaks which coincide with telephone poles, overhead power lines or lamp posts.
Lower HF bands
If interference affects the 1.8MHz amateur band, it may also be audible on an MW broadcast receiver. Alternatively, a ferrite rod aerial with an MW coil can be tuned to the 1.8 MHz amateur band and connected to a portable HF receiver using a 2 turn coupling winding to match into a 50Ω receiver input. For 3.5MHz, the main winding on the ferrite rod should be about 20 turns tuned with a 200 pF variable capacitor. A 1 or 2 turn coupling winding should be used. A ferrite rod aerial is recommended for D/F-ing EMI on the 1.8 and 3.5MHz bands because it can be held right down on the ground to detect the magnetic field from EMI propagating along underground cables as a common mode signal (that is, on all conductors together relative to earth). If properly balanced, a ferrite rod aerial gives a minimum signal when the rod is pointing towards or away from the source but this direction finding property can give misleading results in built‐up areas or near overhead cables because MF/HF interference can travel for hundreds or thousands of metres along Hydro wiring or telephone wiring (particularly if overhead).
Standing waves can cause the signal strength to rise and fall at intervals along the line. With any EMI from overhead cables, it is best to search for it on the highest frequency possible, moving higher as you get closer. If you want to follow overhead power cables across land without a public right of way, permission should be obtained from the landowner before entering. If you can identify which pole is responsible, make a note of its number and report it to BC Hydro. Do it well or contact the right person and they won’t laugh at you. After all they use the word “Authority” in their advertising.
Higher HF bands
The tendency for interference to travel along wiring decreases as frequency increases so it is better to search for interference on the highest frequency on which it can be heard. In practice, it will probably be necessary to listen on a frequency above the MUF where the HF bands are quiet. The 28MHz band is a good band to use and a direction finding loop can be made for the task. Such a loop may not be sensitive enough without a pre‐amplifier however. When you get closer to the source, try to find it on a VHF band but check that the VHF signals have the same characteristics as the HF signals and are not coming from a completely different source!
On 144MHz, it is possible to use a horizontal half wavelength dipole with a balun for direction finding. This gives a minimum signal when pointing towards or away from the source although it can give misleading results if the source happens to be vertically polarized. It is also possible to use a yagi aerial which gives an unambiguous direction bearing. If the source appears to be vertically polarized, the yagi can be used vertically, otherwise horizontal polarization is preferable because the aerial has a narrower beamwidth when used horizontally. A 4 or 5 element yagi is about the largest which is reasonably portable at 144MHz. An HB9CV is of some use but the main lobe is very wide and the directional bearings can 'squint' due to the unbalanced feed. To correct for 'squint', turn the aerial over, take another bearing then average the two.
It is important to remember that at 144MHz, direction finding in a built up area can give misleading results due to reflected signals from buildings, lamp posts, cars, etc. It is therefore necessary to take a number of bearings from different locations as no single direction bearing can be regarded as reliable. If D/F‐ing from a car, remove any 144MHz mobile aerial before taking a directional bearing as this can reflect signals. It should be noted that Time Difference Of Arrival (TDOA) and ring Doppler direction finding techniques are only suitable for D/F‐ing a coherent carrier and cannot be used on random noise from motors or thermostats.
The 50MHz band is less prone to reflections than 144MHz but the only reasonably portable direction finding aerial is likely to be a loop. Another possibility is to use an 88‐108MHz FM broadcast receiver tuned between stations with a 3 element FM aerial.
If EMI can be heard up to the 70cm band, a 10 element 70cm band yagi makes a good direction finding aerial but at UHF, more care is required to avoid misleading results due to reflected signals.
A thermostat which arcs for perhaps 20 seconds every 10 minutes can be most annoying but difficult to find. If it is very close (less than about 30 metres), it may be possible to detect it using a UHF portable TV set with a 10 element UHF TV aerial. The wide TV IF bandwidth is an advantage when searching for a broad band source. The TV set should be tuned to a channel where there is no signal. It is important to make sure that the channel is free of any digital television signals as these look like noise on the screen but with a coarser 'snow' than true white noise. As arcing thermostats are modulated at 100Hz, they produce two darker bands of noise on the TV screen which are darkest when the aerial is pointing at the source. If your portable TV receiver has a video output via a SCART or phono connector, it can be used for locating broad band UHF sources of EMI by tuning it to a channel where there is no signal and listening to the video output via an audio amplifier or crystal earphone. An arcing thermostat produces a distinctive rasping sound which is clearly distinguishable from the background noise. If a suspect gas furnace has a flue which is near the street or near your property, it should be possible to hear when it lights up and switches off, particularly with a fan‐assisted [forced-air] system. If you listen on a portable receiver at the same time, an arcing thermostat will produce a burst of EMI lasting for a few seconds or more each time the furnace turns off and possibly when it turns on. Going from an old mercury switch to a solid state thermostat “may” fix the problem, or create an new one!
If you decide to approach the occupier of a house or flat where you think the source of the interference is, bear in mind that the occupier will probably want to be sure of your identity and your motive before letting you in. It is a good idea to write or telephone first to gain their confidence and arrange a convenient time for a visit. Remember that the source may not actually be where you think it is so you should say that there may be something in the house or flat which is causing interference. In most cases, the only way to prove what is causing the EMI is to ask the owner to switch off various electrical equipment until the source is found. In most cases, there is no fault in the equipment in question and only amateur bands are affected.
A diplomatic approach is therefore essential as the owner of the equipment is under no obligation to do anything about the EMI so it can only be reduced with their cooperation. Any EMI reduction should be restricted to measures which can be fitted by the owner without the need for you to touch or dismantle the equipment in question. In some cases, for example a faulty thermostat, the EMI is likely to interfere with the owner's broadcast radio or TV reception and may affect neighbours.
Commercial or industrial premises
If EMI appears to be coming from an office, shop, factory or other commercial premises, some effort may be required to make contact with the right person. In the case of a large company, there is probably an office services manager, building services manager or technical manager whom you could contact. If you are lucky, there may be a licensed radio amateur working on the site somewhere and he or she could be a very useful contact.
In any case, it is best to write or telephone first and ask to make an appointment to see the appropriate person. With luck and a diplomatic approach, they may be prepared to take you around the site to look for the source. You will need to take a portable receiver as it probably won't be possible for equipment to be turned off.
Reducing the EMI
If you prove conclusively that a certain piece of equipment is producing EMI, it is worth trying to find out full details of the make, model number and date of purchase so that a complaint can be made directly to the manufacturer or importer. A polite and technically well‐informed approach is recommended when dealing with manufacturers. The equipment probably met all necessary standards at the date of manufacture so the only way forward is on a good will basis. The best approach when dealing with manufacturers is usually to phone first and find out the name of the person responsible for EMC then follow up the phone call with a letter, fax or e‐mail. It is also worth finding out whether a newer model is available with reduced EMI. In some cases, the manufacturer may be prepared to provide a filter or exchange the equipment in question for a newer model at a reduced price.
Of course, if none of this works, and you still have an S9 noise floor, you can always move to the country. A good friend has an “impressive” radio shack out beyond 200th among the cow paddies and he has a S-0 [that’s zero] noise floor, yeah… no noise, none, nada, zilch! And there are so many more stations on his radio than mine. He hears the world – I hear Californian and Texan Kilowatts and OH8X with the world’s largest Amateur Radio antenna!
The original article was written by Gary Skett and appeared in The SARC Communicator in September 2011.
Read the entire newsletter at: https://goo.gl/Y2CmJb
Read the entire newsletter at: https://goo.gl/Y2CmJb