R.F. Burns said:
Thanks for the answer. I have a follow-up question. Holding an Extra class amateur license I remember part of the testing had to do with interference concerns. I'll paraphrase; according to the commission, if you are running a "clean" transmitter (harmonic radiation and bandwidth within FCC limits) but your neighbor is complaining about interference to their poorly shielded telephone/TV etc, it is the responsibility of the faulty receiver owner to make the changes needed to prevent the interference, not the operator of the licensed transmitter. Isn't this a similar case, where the transmissions from a broadcaster are clean but the problems reside at the receiver end?
FCC policy on interference remediation is consistently inconsistent:
Example 1: You construct a new 5 kW FM station at the site of a 100 kW FM station that's been in operation for years. The guy who lives across the road claims you're causing interference to his new YORX "entertainment system" purchased the previous week at WalMart -- you investgate and determine it's front end densense of the FM section. Although the 100 kW station is the more likely culprit, the "blanketing rule" says you're stuck fixing the problem because you're the newcomer to the site. But after a year, you're no longer responsible.
Example 2: You want to build a new 10 kW educational FM station on 91.3 MHz in a suburban area served by Channel 6 TV. You show that all other FM stations would be protected against new interfrence. However, the FCC imposes a limit on your ERP such that the total population within the TV 6 interference contour does not exceed 3,000, and you are forced to reduce your proposed power to 2 kW. You might also be required to operate with vertical polarization only - no circular or horizontal. It doesn't matter if the TV sets are actually affected, or if they are connected to cable or satellite, rather than a rooftop antenna or rabbit ears, or if 200 of those people are under age 5 and their parents won't let them watch TV; the rule (47CFR73.525) still applies. However, a commercial broadcaster on 92.1 comes along and proposes to upgrade his 6 kW Class A facility to a Class C1 running 100 kW at a nearby site where the pop density is higher and Channel 6 is weaker, but still provides Grade B service. As long as FM stations are protected, this no problem at all, because the FCC disregards Channel 6 interference caused by any station above 92 MHz.
Example 3: You propose to build a 10 watt FM translator on a rural hilltop within the 54 dBu contour of a Class B commercial FM station 38 miles away, which operates on a third-adjacent channel. The FCC curves predict the Class B has a field strength of 55 dBu at your site, even though the measured signal at 9 meters AGL is 15 dB stronger -- remember this is a hilltop. You must show the FCC that your translator's 95 dBu contour doesn't cover a
single house, even the home of the Amish farmer 400 feet away, who doesn't have electricity or own a radio. Otherwise, the application will be rejected.
Example 4: You propose a new 250 watt translator, rebroadcasting a satellite feed from a primary station 2000 miles away. Your translator will operate on a second-adjacent channel to a local non-comm FM, but you demonstrate on paper (a 1943 USGS topo map) that there are no buildings within the predicted interference contour, hence no affected populationThe FCC says it's A-OK.
Example 5: Same location as above, but you now want to build a 100 watt LPFM (with a local studio) on a different frequency that clears all mileage separations except a third-adjacent station a mile away. The FCC (and Congress) say
absolutely not!
Example 6: You move a high power FM station to an antenna farm overlooking a busy interstate highway and a receiver-generated intermod product begins blocking out another station in the market (which transmits from a site 8 miles away.) Complaints have been filed by commuters, who are upset with this interference to their car radios. However, the FCC says this is not a legal issue because mobile receivers are exempted from the "blanketing" rule.
Example 7: You want to upgrade an FM station and ask for a waiver of prohibited contour overlap based on a Longley-Rice exhibit showing that a mountain is in the path. The FCC says that not allowed.
Example 8: You apply for a DTV station and perform the interference study using a Longley-Rice exhibit. The FCC says that's OK.
And the list goes on and on. Not sure if I've answered your question, though... ???
