July 2002   

Dumbing Down the Dial
Why Your Radio Doesn’t Work Anymore, and Why You Should Care

by PAUL D. LEHRMAN

It isn’t often that I can, in the space of a few days, learn about a new application of digital technology in audio, connect with a part of the audio industry I left long ago, find out more ways our so-called government has been screwing up, find out why consumer electronics manufacturers are not necessarily our friends, and fall in love with a piece of retro gear. And, I didn’t even do all of this in my studio; I did it in my kitchen.

I live in Boston, which, besides being one of the great university towns of the world, is a great radio town. That’s not a coincidence. Almost every college around here, large and small, has an FM radio station. Most of them are down in the noncommercial part of the band, from 88.1 to 91.9 MHz. Some are big boomers, like Boston University’s WBUR, which has a large paid staff and is a major outlet for NPR programming, but it has little to do with the college itself. Others are relative pipsqueaks, run by students or volunteers, like Tufts University’s WMFO or Boston College’s WZBC. Harvard’s station, WHRB, is actually a commercial operation; it’s run by undergraduates, but it sells advertising to augment its budget and broadcasts in the commercial part of the band. The biggest gun in the noncommercial band is WGBH-FM (where, full disclosure dictates, I have helped produce a few shows and Webcasts), which is part of a nonprofit conglomerate that also contains two television stations, several production companies, and a bunch of other divisions that make it one of the most successful entities in American public broadcasting.

The variety that these stations provide to listeners is, as far as I can tell, unparalleled in the country. While commercial FM stations have devolved, under the feudal leadership of the two remaining corporations that own the bulk of them, into the habitats of bottom-feeding shock-jocks and cookie-cutter "alternative" rock and rap, the independent nonprofits at the low end of Boston’s FM band deliver a well-rounded diet of classical, jazz (and I don’t mean Kenny G), electronic, ethnic, punk, ambient and real alternative rock–not to mention news from places other than Washington and Hollywood, and public affairs programs that actually connect with and educate their audiences, and aren’t on the air at 5 a.m. on Sunday.

Am I laying it on too thick? Maybe. But as readers of this column know, I’ve always been a big fan of radio. Even in the age of high-speed Web access, I still believe radio is the best way to get people to listen to music that they haven’t heard yet. And, exposing audiences to new music sells records, which means that someone is booking studio time and buying gear, and that’s why we should all be concerned about what’s been happening to radio.

But that’s a big issue, and I’m going to focus on a smaller one–or at least attempt to. (I may run off a couple of times, try to forgive and stay with me...)

One of my favorite stations around here is WUMB, which is licensed to the University of Massachusetts Boston. 'UMB is the only 24-hour folk-music station in the entire country. It went on the air about 20 years ago, originally using volunteers, and in 1986, hired a professional staff. Its transmitter puts out a middling 660 watts ERP (Effective Radiated Power), and it’s at the top end of the noncommercial spectrum, at 91.9, which means it’s jammed right up against where the much more powerful stations live. The university is on a peninsula jutting out into the Boston Harbor (a beautiful spot that is shared with the John F. Kennedy Library), but the station’s antenna is several miles south of there, on a hill in the city of Quincy, atop a water tower.

In recent years, UMB has been trying to increase its coverage. But upping its power has never been an option: According to chief engineer Grady Moates, FCC rules won’t allow that because it might cause interference to stations, both commercial and noncommercial, on nearby channels. So instead, UMB has been snapping up other available licenses and re-broadcasting the signal from other sites. They now have transmitters in Falmouth and Orleans on Cape Cod to the southeast, in Worcester to the West and in Newburyport up north near the New Hampshire border. The Orleans station is on the AM band, but Falmouth and Worcester are on the same channel as the Quincy transmitter, and Newburyport is right next door at 91.7.

As I’ve watched this process, I’ve been doing more than a little head-scratching. I knew from my radio engineering days that one of the worst enemies of FM reception is multipath interference–the same signal coming to your receiving antenna from several different directions, just enough out of phase to cancel each other out. Multipath is especially a problem in urban areas, where the short RF waves play pinball among the steel skyscrapers. So not long ago, I got in touch with Moates and asked him, "How do you keep the transmitters from clobbering each other?" His reply was, "We don’t. They do."

If WUMB hadn’t grabbed those licenses, however, someone else would have, sooner or later, snatched them up. Moates explained, "While commercial FMs are assigned on a ‘spacing’-only basis, noncommercials are assigned on a ‘contour’ basis." Determining where a transmitter can be located involves plotting signal-strength contours on every channel within 600 kHz of the desired one, as well as plus or minus 10.6 and 10.8 MHz–the value of the Intermediate Frequency in superheterodyne FM receiver designs. (You see, I retained something from those days!) "A new station can then be dropped in, as long as its contours don't touch similar contours of any other station in a way that’s prohibited by FCC rules," he says.

"The Falmouth and Worcester signals were 'holes' on our frequency near Boston that somebody was eventually going to file for, and then their signals and our signal would interfere badly in the overlap areas. So we filed for and got these two stations as a pre-emptive strike."

WUMB’s three 91.9 MHz transmitters, it turns out, are not exactly on the same frequency. "The FCC allows you to be up to 2,000 Hz off-channel," explained Moates. "One is at 91.900088 and another is at 91.899986. If you drive through the overlap area, your radio is receiving both signals, but they're almost never at the same level. So your radio constantly jumps, and every time it jumps, you hear a little ‘phht’ of noise. It sounds like multipath, and it is, but instead of multiple reflections, it’s caused by multiple transmitters. It’s the ‘cellular’ approach to broadcasting."

Even more interesting is how they get the audio on the different transmitters to line up, so that when your radio goes from one "cell" to another, the music doesn’t skip a beat. "We send the program audio to the transmitters as MPEG-2 on a pair of 56k dedicated phone lines," he told me. "The phone company doesn’t offer anything between 56k and T1 service, which would cost us $2,000 a month, and we can’t afford that. They may give lines to some noncommercial stations for free in exchange for promotional announcements, but we’re not big enough for them to do that. So the processing delay through the MPEG encoders and down those lines is about a quarter-second.

"Eventide Clockworks developed a special stereo delay for us, which was based on their profanity delay. It doesn’t use bit rate reduction, like most profanity delays, because we didn’t want to do that twice. They modified it [from a typical five or ten seconds] so that it could go down in increments of half a cycle at 8 kHz. We can set it up to match the line delay, so that the audio to all of the transmitters is phased within 25 or 30 degrees of each other at 5 kHz."

Despite its low power, UMB has loyal listeners, like me, all over eastern Massachusetts. I live on a hill about 12 miles northeast of the transmitter: With a good telescope, I could probably see it. And, up until about a year ago, I could listen to it on an old Sony cassette boom-box while I made breakfast. Upstairs in my studio, it’s always been nothing but hum and noise, but I’ve attributed that to the enormous amount of RF junk my computers and audio gear generates. (Instead, when I’m working, I listen to it on the Web. It isn’t pretty, but it’s better than the beer and junk food commercials on the stations that do make it through the noise.)

Last year, however, the cassette mechanism in the Sony bit the dust. I replaced the boom-box with one of those snazzy, feature-filled Cambridge Soundworks CD/FM two-tweeters-and-a-sub systems. It sounded great on the commercial band and on the big educational stations, but UMB nearly disappeared altogether. When I tried to listen, I’d get occasional little wisps of guitar or hammer dulcimer, which were quickly buried by distortion and hash. Vowing to reclaim my family’s right to listen to Arlo Guthrie and John Gorka over our morning coffee, I put up a rooftop antenna, and with a map and compass, pointed it right at the Quincy transmitter. The noise just got louder. My wife demanded that we bring back the Sony, broken tape player or no.

It wasn’t the three transmitters that were conspiring against me–I’m far enough from Worcester and Falmouth so that they aren’t a factor. And there’s nothing particularly powerful that’s close to 91.9 on the dial that might be blowing it away, so I couldn’t blame it on the new radio’s presumably better sensitivity.

Moates straightened it out for me. In between me and UMB’s tower, directly in the line of sight, are the two biggest transmitter sites in town: the Prudential Center and the John Hancock building. They are pumping out so much FM, TV (including one almost-unwatched station with a million watts ERP), microwave, taxicab calls and God knows what other kind of electromagnetic energy that the tuner in this fancy radio literally can’t pick out that tiny little 660-watt signal from the others–no matter how far away in the spectrum they are.

"All that RF energy is causing intermodulation products," Moates explained. "When two or more stations have transmitter sites near each other, they can mix together and create additional signals on other frequencies that shouldn't exist. By FCC rules, those products are supposed to be at least 80 dB below the main signal, about .01% of the power of the station or less, but when you've got ERPs like 50,000 watts, even 80 dB down is still a considerable amount of energy, when you compare it to our 660-watt signal after it's traveled 10 miles or more. (You can read the actual wording of the rule, if you’re really interested, below.)

"Intermodulation can also happen in receivers," Moates continues. "Digital tuners, especially the cheap ones that they use in these mini-systems, have varactor diodes in the front-end circuitry, which tune the radio when a DC reverse-bias voltage is varied by a microprocessor. When you tune the radio, you're just changing this DC voltage.

"But these diodes are easily overloaded, and when they are, they start conducting forward on the high-RF energy, causing the radio to create its own ‘intermodulation’ products. And that's why you get all that interference.

"It’s a kind of ‘dumbing-down’ of consumer electronics. The manufacturers don’t want to let you adjust anything. They’ve even taken out the ‘Mono’ switch, which you used to be able to use to help receive difficult stations. They’ve replaced it with an automatic circuit that blends the highs progressively as the signal weakens. What you end up with is a mono signal, but you don’t know that because the ‘stereo’ light is still on!"

That’s also why the old Sony boom-box’s tuner worked: It was analog. It's why the $600 over-powered, over-featured digital receiver in my studio can't pick up the station. And, it’s also why the ancient Onkyo receiver in my bedroom can get UMB most of the time: It’s analog, too. And, it has a really helpful "Mono" button.

The manager of the Cambridge Soundworks store that sold me the radio admitted that people don’t buy it for the tuner: "They just buy it for the CD." Another company that produces a high-end tabletop radio has, said Moates, "this beautiful $300 box, which they put a $9.95 tuner in." Moates wouldn’t let me quote him saying the name of the company because of their propensity for taking legal action against their critics. (Another source I talked to said he was once quoted in an article referring to the company as "litigious," and immediately got a call from their lawyer demanding a retraction.)

So where, besides at an antique store, do you get an analog FM radio that can pull in these valuable and underpowered stations in this digital age? Therein lies another tale, which is going to have to wait until next month.

Paul Lehrman–like a vintage tube–is just getting warmed up.


TITLE 47--TELECOMMUNICATION
CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (Continued)
PART 73--RADIO BROADCAST SERVICES--Table of Contents
Subpart B--FM Broadcast Stations
Sec. 73.317 -- FM transmission system requirements.

  (a) FM broadcast stations employing transmitters authorized after January 1, 1960, must maintain the bandwidth occupied by their emissions in accordance with the specification detailed below. FM broadcast stations employing transmitters installed or type accepted before January 1, 1960, must achieve the highest degree of compliance with these specifications practicable with their existing equipment. In either case, should harmful interference to other authorized stations occur, the licensee shall correct the problem promptly or cease operation.
  (b) Any emission appearing on a frequency removed from the carrier by between 120 kHz and 240 kHz inclusive must be attenuated at least 25 dB below the level of the unmodulated carrier. Compliance with this requirement will be deemed to show the occupied bandwidth to be 240 kHz or less.
  (c) Any emission appearing on a frequency removed from the carrier by more than 240 kHz and up to and including 600 kHz must be attenuated at least 35 dB below the level of the unmodulated carrier.
  (d) Any emission appearing on a frequency removed from the carrier by more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.
  (e) Preemphasis shall not be greater than the impedance-frequency characteristics of a series inductance resistance network having a time constant of 75 microseconds. (See upper curve of Figure 2 of Sec. 73.333.)

(Grady Moates adds: This is a change from earlier years. ...notice that there is no "minimum" pre-emphasis. This means that a station could, if it so desired, operate flat. Hmmmmm.... )


These materials copyright ©2002 by Paul D. Lehrman and Primedia Business Publications