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November 01, 2006


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"43 percent of satellite radio subscribers would cancel their service, or not have signed up in the first place, if the satcasters did not have music."

Shocking. I would have placed it closer to 99%.

Reilly Liebhard

NPR's complaints are pure crap. I recently purchased a Belkin TuneCastII (FCC type-approved, and able to tune all frequencies on the USA FM band, in 0.1 MHz increments.) I was visiting family in a suburban area where the signals from the city broadcast farm have a theoretical strength of 72 dBu (four times the 60 dBu "city grade" signal strength, which defines the territorial extent of FM stations' legal protection from interference.) Long story short, I got bored and attempted to see how far the Belkin could "take them over." I had to get within EIGHT INCHES of the car's receiving antenna to overtake these signals reliably.

This tells me the Belkin's signal had a strength of 74 dBu at 0.7 feet (to account for the fact that the FM "capture effect" requires a slight buffer in order to choose the stronger signal.) In turn, this means a signal strength of 54 dBu at seven feet (54 dBu = 1/10 of the field strength of 74 dBu on the logarithmic decibel scale, and field strength varies linearly with distance since the inverse-square law applies only to dissipated *power.*) This would be enough to overtake only a 52 dBu signal -- which is only 45% of the signal strength of an FM station's legally protected 60 dBu boundary. (Not to mention, it suggests that the 48 dBu signal -- half the strength -- goes out for 14 feet. Given the mathematical difficulties in working with such small distances, as well as the fact that the licensed stations I was using as reference signals might not have lived up to their full theoretical signal strength in reality, this looks like substantial compliance with the Part 15 standard of 48 dBu -- or 250 microvolts per meter field strength -- at ten feet from the antenna.)

Owing to the "city grade" rule, a 52 dBu signal has no legal recourse against, say, atmospheric interference from other licensed stations -- or even regular interference from a licensed station sited close enough that the two stations' fringe signals clash with one another. (This happens all the time on the low end of the band in Chicago -- THREE licensed educational signals on 88.1 clash with one another on the fringes of the downtown Loop, at signal strengths in the high 40s and low 50s dBu. And even here in Minneapolis, with a much less crowded band, community station KFAI doesn't get out very far past its 50 dBu before hitting interference from an upstart Christian satellite-fed station on the same frequency, located around 40 miles to the northeast.) I would argue that a Part 15 type-certified device (i.e., one that's been field-tested and approved by the FCC's own engineers) is equivalent to a licensed station for purposes of interference protection, since it meets the legal requirements of its authorizing rule section the same way a licensed station meets ITS requirements... meaning that no station has a leg to stand on about modulator complaints outside its 60 dBu contour.

And all of the above assumes the conditions most favorable to signal takeover! My override test took place in open air, with an obstacle-free line of sight to the antenna, and the unit held vertically so that its internal antenna wire would directly parallel my vertical car antenna (i.e., the polarization patterns would match.) In reality, these units would be operating inside a car (the frame of which would cut several dB off any escaping signal), with no guarantee of vertical alignment, and well more than ten feet from the next car except in the rare case of "convoying" on a freeway. Not to mention -- for the sake of the user's OWN enjoyment, s/he would most likely not use any kind of occupied frequency, even a 50 dBu fringe one! Two FM signals at almost exactly the same strength on the same channel generate a very characteristic (and very annoying!) "signal-mixing squeak" behind the audio. (And if you climbed a hill that favored the line-of-sight to the broadcaster, they might well override you completely.)

I could only see a couple of ways that these broadcast stations are really being interrupted. One would be that these incidents are occurring at a very deep fringe of their signal coverages (either due to a sudden obstacle -- in which case banning the modulators would effectively be making national policy based on a rare confluence of circumstances; or due to distance from the transmitter -- in which case the FCC, through its definition of city-grade protection, has made it pretty clear that "crap happens" in the realm of secondary signal strengths.) The only other possibility is that someone really is using an over-powered unit. However, since the tentative science above has at least *suggested* Belkins (one of the most common units) are compliant, a proper response will require a much more targeted effort than the knee-jerk ban and recall (or Part 15 amendment) that NPR et al. seem to be pushing. Maybe they could call for investigation of specific brands to see if they really do comply with type-acceptance requirements, or undertake a public education campaign of some kind in local radio markets, urging people to be courteous in their frequency selection just as they would in any other aspect of life.

BUT -- for a number of other reasons, I don't see this kind of measured response on the horizon. Several commentators have expressed the opinion that NPR really isn't as "public" in its mission and spirit as it would like us to think. I can say this is definitely the case with our *state* public radio organization -- they wanted to use one of the few possible LPFM frequencies in this town for a downtown Minneapolis translator (i.e. relay) station of their full-power classical signal, which they claimed suffered from "multipath" (i.e. self-cancellation) interference due to bouncing off the downtown buildings. (This translator would have destroyed fringe reception of a local college broadcaster on the next channel down, at least as far as the station's 50 dBu contour or so. How ironic.)

For reference, the 100,000-watt main station they wanted to relay transmits off the Shoreview antenna farm, 1015 feet in the air and a scant twelve miles from downtown Minneapolis -- putting close to a 90 dBu signal into the area. This is the kind of signal that will be rendered cleanly by a $5 Wal-Mart ear-bud radio encased in a lead box. I live a few miles closer, near the 100 dBu contour, and there it's strong enough to "overload" both of my component tuners, so that they hear the classical station [and other Shoreview signals] at random spots all over the dial unless the antenna is aligned just so. If this 90 dBu signal were somehow cancelling three-quarters of itself by reflection, it would still come out at 78 dBu, and it's been my experience that even the cheapest Walkman can pick up signals above the mid-60s. If it were cancelling nine-tenths of itself, it would still come out at 70 dBu. If it were cancelling *ninety-five percent* of itself, it would still come out as 64 dBu, i.e. above the protected city-grade strength. Somehow I have difficulty seeing why this translator was really needed, except as a kind of unfortunate leg-lifting on a spectrum tree of limited height.

This sort of translator behavior -- as well as alleged improprieties in seeking public funds to acquire WCAL-FM from a local private college; MPR's ownership of (and in some cases station license registration under) a for-profit arm known as Greenspan Media; the well-documented attempts of MPR since the 1970s to get its hands on the Minneapolis Board of Education's jazz station and other truly independent local public broadcasters; the extremely high fees NPR charges its member stations for even small amounts of programming; and NPR's successful push to destroy the "Class D" 10-watt FM school station license in 1978 -- suggests that we as a public might benefit from a healthy skepticism as to what our LARGE state and local "public radio" organizations are really aiming to accomplish... whether it's with regard to modulator complaints or anything else. To me, it seems as if NPR & Co. are making common cause with the folks above 92 MHz. Perhaps, like many commercial broadcasters, they fear that their conservative "don't rock the boat" programming philosophies, and sometimes lack of live DJs, is about to bite them in the butt by rendering them obsolete in the face of emerging satellite technology. Perhaps they fear losing dominance over the airwaves, and are responding with a tactic lifted right from the rest of our litigious society, appealing to the legal system as a tool to serve their personal interests.

phil fraulino

I see you agree with the New York Times. See Business Section, Thurs. Nov 4., 2006
I'm sorry I disagree with you in part. We should unite with our NPR friends since they are closer to us than the commercial stations above 90 mhz. There are also few college radio stations also at the 105 mhz plus side for your information

Phil Fraulino


can we put a character limit on these blogs? that was annoying.

how about using a link next time smarty-pants?

Reilly Liebhard

My apologies, SueB. It was awfully silly of me to think that a "comments" section was the right place to put a comment. Forgive me for contributing.

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