I'm not sure what you mean that I'm like a pole that goes with the wind. However I'm not going to be the only one going Ra Ra Ra blah blah blah on a topic of change if the interest doesn't show the same for the rest of the folks here. Getting back to this topic AM at the moment has more legal range than FM does.
DJboutit, I've got to give Thelegacy extra credit for being a sharp and conscientious Part 15 broadcaster. However, the FCC will NEVER have any complaint with a Part 15 broadcaster who happens to be on the same frequency as another station that is receivable due to unusual atmospheric conditions.
Every FCC licensed FM has an "interference-free contour". But if you live in, say, New York... and an FM from Wisconsin happens to be coming in on your radio due to unusual atmospheric conditions, there is no expectation or obligation that any licensed or unlicensed broadcaster must all of a sudden sign off and protect that distant signal. Because it is not part of that distant station's interference-free contour.
With AM? Just be nice and don't interfere with a local station at any time... or a high-powered distant station at night that might reasonably have listenership in your local area.
(My qualifications to give this advice? I'm just an average guy, but I've been an FCC rules freak for 46 years, and have been an FCC-licensed radio station owner for 33 years. I've gotten this information from broadcast lawyers, and have paid those &@$+@^$ enough legal fees over the years to buy another radio station! 🙂
Thelegacy's basic point is well-taken, though. Do not exceed legal power, and do not interfere with radio stations that your neighbors can and might listen to.
That makes sense Marosborne, it's probably the same idea as the low night power levels that most daytime AM stations are allowed to use, with power calculated using Nighttime Interference Free contours (NIF) of higher power stations on the channel. That would seem to be how Traveler Info Stations can operate around the clock even when there's another dominant station on the same frequency that skips in overnight.
In response to legacy's interpretation of broadcast rules in the US...
Only the 60 dBu contour of most FM stations are protected. Any coverage outside of the protected contour is subject to any interference that occurs. And certainly any reception caused by atmospheric conditions is unpredictable and not protected.
"Every FCC licensed FM has an "interference-free contour."
Hi. Not entirely correct. In many cases LPFM's must except interference from other licensed stations.
Thats because LPFMs are considered secondary services. I think even FM Translators get priority over LPFM. LPFM is pretty low on the broadcast totem pole.
All FM classes C B and A get interference free zones. D, FM Translators, and LPFM do not.
The best legal range on part 15 FM would come from using a transmitter that put out 250uv/m equally well in every direction on a sphere 3m away from the antenna. It would be constructed specifically to the channel you want to transmit on, and after being installed it would be verified with a field strength meter to make sure no interactions with surrounding objects, surfaces, mounting hard ware, or anything else caused the field in any direction to exceed 250uv/m@3m. Something that did that would be expensive and not very flexible.
The best legal range on part 15AM would be using an output stage that took the allowed power and wasted as little as possible in the transistors. Then it would be coupled into an antenna with as efficient of a matching network as possible. It would be installed over salt water or highly conductive earth. Super-efficient part 15AM transmitters are available at reasonable prices. Then the trick is getting exactly the legal power without going over, and installing it in such a way that even the most hateful inspector could not find fault with. So a super-efficient transmitter just at the input to the final stage power limit installed directly above the ground so the total height of the antenna above ground is 3m. Just under the ground, put as much copper as you can afford. For example, the FCC’s idea of a full power AM ideal ground would be 120 radials .25 wave lengths long with mesh directly under the transmitter with everything brazed together. It is possible to chemically increase the conductivity of the ground in the radial field if desired, but that has environmental and economic implications. AM will give you more range, but getting the perfect ground would cause your transmitter to be somewhat far from potential listeners.
I totally agree as i was discussing this vary fact in some huge detail last night before my Wife had a low sugar attack. We as part 15 folks are at lower priority than secondary services. So with LPFM at the bottom of licensed services you can bet your bottom dollar for example if my Wife's Dr friend asked me to move my station and I was a dumb A hole and said "Well that station is not protected because the signal only comes in some times while there is an inversion and kept transmitting right along on 96.3 I bet the next thing that Dr friend would have done was to have called the FCC and told them about how The Legacy was refusing to move off 96.3 so he could hear his country station which only came in once in a while. They would come and keep in mind that some of these certified transmitters that we think are 100% within the field strength limits may not be and that gives the FCC more to put down as your list of voilations. But playing nice like I do goes a long way so that if my transmitter unknown to me went over and I was found to have gone over they may tell me "Hey you need to turn down the power or get a legal transmitter!" They could even offer a way to fix mine. We have seen cases where when someone plays nice it goes further than acting like Rika FM did. I'd move to AM if need be anything to make the neighbors happy.
Station 8 is working on antenna designs for AM that I can use indoors. The TASH antenna looks like a good one but he is working on some others.
"Well that station is not protected because the signal only comes in some times while there is an inversion and kept transmitting right along on 96.3 I bet the next thing that Dr friend would have done was to have called the FCC and told them about how The Legacy was refusing to move off 96.3 so he could hear his country station which only came in once in a while. They would come and keep in mind that some of these certified transmitters that we think are 100% within the field strength limits may not be and that gives the FCC more to put down as your list of voilations. "
The FCC wouldn't give him the light of day. That would be a collosal waste of their time.Its good to be on the safe side of things, and I don't disagree with you on finding the cleanest frequency possible. But shutting down or moving just because a station happens to skip in is insane, you would never find a frequency to use. Especially on AM.
There are zero legal reprocussions on operating on a frequency that under most circumstances is clear. Skip is not, and has not ever been protected on the FM broadcast band. In fact, thats why the FM band moved from 49 mhz!
Skip is not, and has not ever been protected on the FM broadcast band. In fact, thats why the FM band moved from 49 mhz!
Note that the eventual assignment of the FCC of the 88-108 MHz spectrum for the FM broadcast band in the US reduced, but did not eliminate all possibilities of interference from other co-channel stations in that 88-108 MHz spectrum -- for which all such stations are dependent on propagation conditions.
Even VHF channel 2 was low enough, I think about 54 MHz, that it tended periodically to be messed up by skips from other channel twos in other cities.
I am only guessing, but was the old FM band also moved to make way for TV channels?
@ Post #20. True, wdcx. LPFM's have a quasi-protected service contour of 60 dbu at the time they are licensed. Subsequent to that, they must accept any interference that happens from "changes to a primary station's facilities" (the FCC's language).
That's kind of drifting away from my core point that we Part 15-ers don't need to worry about protecting distant stations that hop into our towns due to unusual atmospheric conditions.
But wdcx is correct in alerting us to watch the LPFM's, too, even if we guys are operating outside of an LPFM's 60 dbu contour. Good point.
NEC is an excellent program and free.
You can use it to model any type of antenna, CB, ham, television and AM/FM broadcast antennas.
I suggest you all download it and start learning how to use it.
https://en.wikipedia.org/wiki/Numerical_Electromagnetics_Code
Bruce.
@Carl
IIRC the FM broadcast band was moved due to a combination of probablematic skip, TV broadcasts, and pressure from RCA to take out some competition.
You are right Mighty 1650.
RCA was a major player in the early fate of FM.