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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.
.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
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.
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