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Low Power FM Report Rejects Interference Concerns
akb writes "Back in 2000, Slashdot covered the Low Power Radio setback by Congress, detailing a law which gutted an FCC initiative that would have created thousands of Low Power FM radio stations (LPFMs). Congress overruled the FCC, ostensibly because of interference concerns, and cut the number of stations from thousands to a few hundred, with hardly any in urban areas. A concession was made to allow a study of the interference caused by LPFMs, and that report has been released. The verdict: 'Based on the measurements and analysis reported herein, existing third-adjacent channel distance restrictions should be waived to allow LPFM operation at locations that meet all other FCC requirements, [with the exception of several minor technical requirements]'. There's more coverage at DIYmedia.net"
Seattle area has that - 104.3, 104.5, 104.7, 104.9 . Just noticed that last night.
7/11/03 - Long-Overdue LPFM Interference Report Complete: No Third-Adjacent Channel Protections Necessary [link to this story]
.pdf format:
When Congress gutted the low power FM service enacted by the FCC in 2000, it reduced the number of available LPFM frequencies around the country by more than two-thirds by implementing "third-adjacent channel spacing protections." This forced LPFM stations to find a clear frequency with at least three channels separating it from existing local stations, which in urban areas is all but impossible. This single fact alone cut the number of potential LPFM stations from thousands to a few hundred at best, with most of those located in rural or suburban areas.
The passage of the "Radio Broadcasting Preservation Act," however, did contain one caveat: the FCC was mandated to conduct an interference study to make sure the third-adjacent channel protections were necessary. The study was to be completed by February 21, 2001. It was actually finished in March, 2003, by the MITRE Corporation, who subcontracted the field testing of temporary LPFM stations in seven communities around the country.
The Amherst Alliance, upon discovering the report was finished but the FCC was sitting on it, filed a Freedom of Information Act request in May to make it public. The FCC blew it off, and correspondence escalated to a point where members of Congress might have gotten involved and/or a lawsuit to force the disclosure might have been filed.
This week, mysteriously, the 700+ page report was published in the FCC's Electronic Comment Filing System. No fanfare whatsoever, not even a note to those of us behind the FOIA effort to let us know it was available. The reason may be due to the following conclusions:
"Based on the measurements and analysis reported herein, existing third-adjacent channel distance restrictions should be waived to allow LPFM operation at locations that meet all other FCC requirements [after four small revisions]...
The FCC should not undertake the additional expense of a formal listener test program or a Phase II economic analysis of the potential radio interference impact to LPFM on incumbent FPFM [full-power FM] stations...Perceptible interference caused during the tests by temporary LPFM stations operating on third-adjacent channels occurred too seldom, especially outside the immediate vicinity of the sites where the stations were operating, to warrant the additional expense that those follow-on activities would entail."
And the National Association of Broadcasters and National Public Radio, who played Congress like a fiddle by claiming that LPFM stations would wreak havoc with their signals, may want to chew on this tidbit especially thoughtfully:
"In terms of the impact of an LPFM station due to interference on the audience of an FPFM station, in the worst case measured, the fraction of the protected coverage area of an existing station that could be subjected to harmful interference is 0.13%. In most other cases, this fraction is orders of magnitude smaller."
Download the four main documents from the LPFM interference report here, in
Section 1 (MITRE Final Report, 4.4 MB)
Section 2 (Comsearch Field Test Plan, 2.4 MB)
Section 3 (Comsearch Test Procedures Plan, 664K)
Section 4 (Comsearch Field Measurement Data, 5.1 MB)
A cursory glance through the field data collected for the report brings up some additional interesting tidbits.
Comsearch (the subcontractor who conducted the field tests) placed public notices in the each test location's major newspaper and had announcements of the LPFM interference test played on the full-power FM station in the area closest to the frequency on which the test would take place. In each instance, no public complaints of LPFM interference were received, although interference complaints were received at some test locations that involved sources other than the test LPFM transmitter.
Most interesting quote from the field data sec
Seattle area has that - 104.3, 104.5, 104.7, 104.9 . Just noticed that last night.
.5 MHz signal bleed, combined with the fact that you'd be quite a disatance from any of the three other stations.
.5 MHz bleed and the .2 MHz seperation co-exists. The FCC never puts stations that close to each other right next to each other, there's always a noticiable distance between the stations. There plenty of spots where stations .2 MHz overlap, and most radios are good enough to follow the carrier of the station they're tuned to in that situation because there will be a dramatic difference in signal strengths between the two.
What you're actually hearing as far as I can tell is:
104.3 KAFE Bellingham
104.5 KMIH Mercer Island
104.7 KEEH Spokane
104.9 KFNK Eatonvile
And the distance between those four cities is kinda the point. You as a listener can hear all four stations pretty well in your car in Seattle, but none of the four actually have their transmitters there. If you were standing next to any of the four stations towers, you'd likely hear just that station and the other three would be wiped out by the
That's how the
RDBS is the name of the technology, and it's been around for a long time. Back in the 80s, some people had pocket devices that gave them stock market quote streams. Don't know what other applications there are, but lots of FM radio stations generate a little extra income by providing RDBS services on their sideband. And you can buy RDBS radios that provide program information and such, though they've never been popular. Here's an expensive toy that lets you say "Tune to an oldies station".
Trust me, you don't want to use hacked Mr. Microphones or real estate promotional transmitters to get on the air. If you're interested in broadcasting, affordably, with an FM transmitter, and you are halfway handy with a soldering iron, check out the kits this British outfit sells (they ship internationally):
http://www.broadcastwarehouse.com/ (click Kits, Modules & Parts)
Pretty easy to put together and they work very well. Or you could buy one of their pre-assembled jobbies.
Another company specializing in FM kits is Veronica:
http://www.veronica.co.uk/
I built one of their 1 watt PLL kits, and also purchased a 25 watt amp. Great stuff, cheap, well designed. Buy a Cushcraft vertical antenna and you're on the air in style.
I wrote in favor of the report, in favor of returning to the 1,000 watt power level that was in the proposal before congress got a hold of it, and elimination of the congress mandated 3rd channel guardbands.
In short, the way the FCC had it in the first place before NPR and the NAB got to it. You can do it online following the instructions at DIYMEDIA. It may not make a difference in the final outcome of at least I got my two cents in, and as a commenter, I get copies of all other comments made on the issue from the FCC!
The problem isn't the LPFM station, it isn't the FPFM station, it's the poor selectivity of FM receivers. 50-60dB is entirely practicable for low cost portables, and at least 80dB should be the norm for higher priced home audio equipment. But the honest truth is that manufacturers aren't going to give you any better performance unless customers ask for it (ie, complain). They can use every channel in sub-$100 "cable ready" TV sets, so they can certainly build affordable "high signal density" FM radios--if there's a market for them.
Yes. If you mean stations that play the music you like, then yes, you will.
You will trot your geeky li'l butt over to here (if you're a digital geek) or to here (if you're a radio geek) and get yourself a transmitter. (You have to build and tweak the North Country Radio kit, but I think it has slightly better specs. I like my MPX96 just fine, and by buddy likes his PCS card, too.)Then you can play the MP3s you like and everyone else be damned!
BTW, these are legal with or without the LPFM regulations because they're under 100mw. The range is about 100-200 feet, or up to a quarter mile with a longer antenna (but you might be pushing it, legal-wise, at that range.)You were 80% angel, 10% demon. The rest was hard to explain. - Over The Rhine
"Math in a song is good."-Linford
Where are you getting that 500 kHz "bleed" value from?
I've looked at more FM radio spectra than I care to count, and they've all been well bounded to 200 kHz - in fact, show me an FM broadcast station that has more than -60 dBc more than 200 kHz away and I'll show you an FCC engineer writing a Notice of Violation.
Now, crappy old FM radio receivers may have had poor IF responses that wouldn't block an ajacent channel 500 kHz away, but that is poor design on the receiver, not a flaw of the format or of the transmitter. A modern system with a synthesized LO and crystal filters has no problem filtering signals at that spacing.
www.eFax.com are spammers
IANAL, but my wife IS, and is currently studying for her BAR exam. Why is that of interest? The Constitutional law part.
It seems that literally ANY point can be argued as a breach of the commerce clause.
As proof I give you Katzenbach v. McClung. (ollie's BBQ)
A tiny, tiny local BBQ joint didn't want to serve blacks (only allowed take-out). Title II of the Civil Rights act claim is made against BBQ joint.
from THis website: Katzenbach v. McClung,44 (Ollie BBQ), held that since 70% of meat served at a restaurant located only 11 blocks from a major interstate highway is subject to interstate commerce, noting a "rational basis" for finding discrimination in restaurants had a direct and adverse effect on free-flow of interstate commerce."
Your paper plates could come from out of state. POWER and Electricity can come from out of state. Telephone service, etc.
Every BAR prep course recommends you trot out the commerce clause to question the constitutionality of anything- because its so damn broad.
P.S.- when I showed her your post, she giggled.
In the future, I would want to not be isolated from my friends in the Space Station.
the big deal about LPFM is not what music gets played on the air. free speech doesn't mean some dj picking out the music s/he likes--it means somebody going on the air and actually having something to say. it's about letting communities getting together and deciding who gets airtime before an election instead of corporations selling it off to the highest bidder. it's about underground news media having somewhat equal footing with the mainstream.
music is nice. but it can be incredibly trivial. people are getting their panties all up in a bunch over clear channel playing shitty music when the reality is that before clear channel bought up all the big radio stations around the country, those stations were still just playing music and promoting concerts and tipping you off to the morning commute.
The Court in recent years has clamped down on the Commerce Clause a bit. They've thrown out a few criminal laws that based their jurisdiction on nebulous commercial effects like those you mention. The Court has shown a new interest in these cases in protecting traditional state powers by requiring more direct connections commerce.
The idea is that modern commerce is virtually all of interstate nature due to technology, trade and other advances since the Constitution was written. These new cases are pushing back on the requirement that something is actually commercial. For example, national regulation of crime and illegal drugs in our country has been based on their indirect effects on the economy. It's not clear exactly how commercial something will have to be, but it is clear that the Court is starting to take the words Interstate Commerce as an actual restriction again.
Two cases to look up are Lopez and Morrison if you want to understand the modern contours of the Commerce Clause. You can find both at Findlaw.
There's also an excellent article by Lawrence Lessig called Translating Federalism that discusses the impact of these cases. You'll have to go to your nearest law library to fin dit.
In many big cities the (NY, LA and Chi for 3), there's a full power (50 or 100 Kw) station every four channels (800 Khz) starting at 92.3 and ending at 107.5. In the '60's, the FCC realized that this channel allotment scheme meant that there were no frequencies (FM channels; the FM band is channelized, where 87.9 is channel 200 and 107.9 is 300) for local stations in suburbs. The FCC's answer was to allow class A (local) FM stations IN BETWEEN the bigger stations. This means that in these cities, there's stations ALREADY located 400 khz (2 channels) apart. Look at LA for example: The class B (50 Kw) stations are on 92.3, 93.1, 93.9, 94.7, etc. But in between there are suburban (3 and 6 Kw) FM stations on 92.7, 93.5, 94.3...all the way up to 107.1! If these 50 and 3/6 Kw stations can co-exist (and they have - for decades!) two channels apart I can't understand why a 100 watt LPFM can't either. Oh WAIT... we're talking Clear Channel, The NAB, and Congress here aren't we? The laws of physics don't APPLY to them! Never mind!