Wednesday, August 7, 2013

AM Radio: No Longer Practical?

Noise from modern electronic devices are killing the media

This is a popular article among my pieces of writing at

(Photo by Patrick Fitzgerald/Barelyfitz)

History tells the pollution has been the repeating problem which the civilization must solve. The radio airwaves are getting polluted too. I fear that AM radio broadcast will no longer be practical if modern electronic devices with the switching power supplies and computers become ubiquitous and necessary to maintain our lifestyle. Conversion or migration from AM to the FM radio will be an easiest way to solve this problem, at least for the dense population areas.

I’ve been struggling to listen to the AM radio inside my house for many years. I think the listening condition in my house might be still better than that of the other people. If I tolerate the buzzing tones,I will still be able to enjoy the programs. I have to keep the small radio receiver away from the cell phone units or anything running computers or other wireless devices, though.

I can no longer listen to the radio near my LCD displays, the laptop computers, and the tablet devices, without proper shielding of the radio and the external antenna outside the house in the open space. I can’t listen to the radio when I’m in the restroom equipped with a Washlet; the water spraying unit is driven with a switching power supply, which generates the noise effectively blocking the radio station signals.

AM radio, or the medium wave frequency broadcasting on 540-1710kHz in the Americas (531-1611kHz in the rest of the world including Japan), has been popular for more than a hundred years. The transmitter often requires nearly a few hundred kilowatts to cover the entire nation, but it works very well, especially during the nighttime when the ionospheric propagation enables the airwaves to reach much further than that in the daytime. For example, in Japan, NHK Radio Two Tokyo at 693kHz transmits 500kW from the antenna site in Kawaguchi City, Saitama, covers nearly twenty million households even during the daylight hours, and is heard very well regularly in Osaka and the other regions nationwide.

The AM in the AM radio stands for Amplitude Modulation. AM radio listeners only needs a simple equipment to convert the radio signals into the sounds. Crystal radio receivers, which have been widely used since the beginning of the 20th Century, are the simplest form of radio. They still work well when the transmission site is near enough. Most of the modern radio receivers convert the frequency of the received signals to the audio frequency range signals, however; superheterodyne receivers is the de facto standard since the transistors got commoditized in 1960s. You can even listen to the AM radio through the digital signal processing technology, on the software-defined radio receivers. So the technology is still alive and thriving very well.

The problem is, however, that more and more electronic devices emit various type of noises on the same frequency spectrum which is used for the AM radio, from the power suppies. It’s not just Washlet; it’s everywhere from the laptop computers to the LED ceiling lamps.

Modern power supplies use the technology called switching voltage regulation; the power supply acts as a high-frequency automatic switch to control the energy flowing into itself,and sends the energy to the devices. The output voltage is controlled by the ratio of the periods of turning the switch on and off. The switch is rapidly controlled to maintain the stable output voltage in the frequency of many hundred thousands times per second. This rapid-switching technology is essential to maintain high power conversion efficiency and low power loss, which cannot be achieved by the legacy power regulation technology called series voltage regulation, which does not use the rapid and abrupt switching, but generates considerably more heat and is much less efficient energy-wise for continuous voltage regulation.

Unfortunately, power switching causes generation of strong electromagnetic noise of the very wide spectrum, and the switching frequency itself is close to the one for the AM radio. The first switching power supply I saw was that built into Apple II computer in 1979. It was large, but still much smaller than the equivalent legacy series-regulated one. I immediately noticed that the sound coming out from the radio near the Apple II suggested how the CPU was working; computers then were not shielded well. I could also hear the power switching sound, emitted from the small voltage transformer inside.

The switching voltage regulation technology is so pervasive that now I see virtually all digital device around me are attached to the switching power supplies; the USB wall warts, laptop PC AC adapters, and the units built into various appliances from computers and even to the commercial and amateur radio transceivers, for more efficiency with less energy consumption. Reverting back to the age of series voltage regulation is simply impractical; no one will want to carry around a power supply which weighs many kilograms for a small laptop or a smartphone.


Modern radio modulation schemes are robust against various sources of noise. AM radio uses the voltage level, or the amplitude, of the airwaves to carry the information, and there’s no effective way to prevent the noise coming into the received signal. On the other hand, FM radio, whose FM stands for the Frequency Modulation, uses the pitch or frequency of the airwaves to carry the information, and the level of the signal is irrelevant unless it is very weak. So FM radio is more robust against the airwave noise than the AM radio and far less affected by the digital devices such as computers.

Then why don’t we convert or migrate from AM radio to FM radio? FM radio consumes much wider frequency spectrum to broadcast, and much higher frequency to broadcast about a hundred times of the AM radio (88~108MHz in most parts of the world; in Japan it’s 76~90MHz). Airwaves of that frequency range cannot use the ionospheric propagation, so FM radio stations do not reach as farther as AM radio stations do, and require considerably higher cost for the simultaneous nationwide coverage.

Let us get back to the original question: can we stick to the AM radio for direct broadcasting to indoor radio receivers, even under the condition that the number of devices emitting noise will be continuously increasing? My answer is no. AM radio will still be useful for serving outdoor and rural area listeners, and in case of disasters and emergencies, because the receiver cost is relatively low. For the urban areas, however, people will no longer be able to listen to the AM radio in adequate quality without erecting the external antennas; conversion or migration to the FM radio will be a practical and feasible plan.

Note that the AM-to-FM conversion is nothing new, especially for people in North America; many stations there have AM and FM simulcasting stations. And in Japan, especially on a coverage of important events, simulcasting between AM, FM and TV stations is frequently conducted. I am talking about the conversion, however, simply from the listening quality perspective, under the noise-bombarded radio spectrum environment in modern houses and buildings.

I’d like to propose providing simulcast in at least one FM radio channel for each AM radio stations in the urban areas. I think this is one of the most practical way to raise the listening quality of radio programs.


Note 1: some may claim internet radio stations will completely substitute the radio services over airwaves. I do not buy that idea because internet radio stations usually suffer a lot of delay of tens of seconds, which renders them useless for emergency or disaster warnings, unless another dedicated side channel is provided.

Note 2: some other people will also claim FM radio is very hard to listen to without an external antenna, which is unfortunately true. I think listening to the FM radio of quality sound is still much easier than to the AM radio based on my experience; FM radio antenna is smaller and less prone to electromagnetic noise inside the house, and is easier to erect.

Exported from Medium on August 7, 2013.

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