Taken from the FCC website this evening
Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice Opens a New Window.(still in effect). On the AM broadcast band, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR Sections 15.207, 15.209, 15.219, and 15.221. These devices must accept any interference caused by any other operation, which may further limit the effective service range.
I must be reading old websites i was thinking AM was regulated in the MW band by wattage and antenna restrictions not by physical distance ...???
https://www.fcc.gov/media/radio/low-power-radio-general-information
JOE..
The FCC website has always had that in it, just a generalization for people that aren't as familiar with the rules. Part 15.219 only limits antenna height and power input.
If you have 100mW unmodulated into the final amp and a total of 3 meters max for the antenna and ground wires you wouldn't go more than around 200 ft. give or take depending on the radio.
But....it wasn't considered that loading coils and ground radials would come into the picture as a loophole in the rule that doesn't change the antenna length or ground wire length so this was a way of getting more distance.
Mark
That 200 feet range for AM comes from an FCC Service Bulletin. It has nothing to do with the actual rules.
I alway read people's comments about how using range masters etc they get out much further legally so this has peaked my interest, and I am up to the challenge.
I am seriously thinking about simultaneously am station and a shortwave station on 13.560 MHz here in Iowa... Right now I am looking for fcc approved devices for transmitters and looking for a console and software very excited etc
Joe
Joe,
Your question about the 200 foot range has been covered and I just wanted to add some information based on my experience which pertains to getting the best range possible.
There are two operating modes available under Part 15 considered here excluding carrier current, one has no physical limits on the transmitting system but limits field strength at a distance and is regulated by Part 15.209. The other regulates the physical properties of the system and is covered in Part 15.219. Significantly more range is possible when operating under the second cited rule than under the first.
The best range will result if ground radials are used (my system has 12 ten foot long radials buried slightly below the sod), a resonant antenna is used (I use a base coil loaded antenna carefully tuned to resonance but some transmitters include the coil inside the transmitter), and a transmitter with high efficiency is used (mine is a home designed and built unit which delivers 85 milliwatts into the base coil of the antenna system.) With this my station can be heard comfortably on a car radio 1 mile away and is noisy but recognizable at 1.3 miles away.
The transmitter is mounted at the base of the antenna at ground level and the system complies with the power input, out of band emission limits, and dimensional limits of 15.219.
This should give you some idea of what to pay attention to when putting together a system and what to expect in the way of range.
Neil
Recently changed, BETS-1 allows either a field strength with no physical restrictions or the 100mW and 3 meter antenna /ground length. You have a choice.
Mark
There are several reasons why the Rangemaster is one of the premier Part 15 AM transmitters, and gets the most range.
Perhaps the biggest factor is that with the Rangemaster, you can tune the input power to the final stage of the transmitter to be EXACTLY 100 milliwatts - most other production transmitters can't and don't do that, as they don't want to go over that limit due to production vagarities.
The second reason is that the final stage of the Rangemaster is relatively efficient, so it takes full advantage of that input power. The only transmitter I'm aware of that may have a final stage that is more efficient is the AMT5000, and it is more difficult to tune to take full advantage of that efficiency.
The end result is that the Rangemaster produces a field strength that is significantly greater than most production transmitters, and field strength = range, all other things being equal. As an example, in the AM transmitter shootout performed over at Hobbybroadcaster.net, a tuned up Rangemaster had a field strength that was twice that of the Talking House. And that was with no radials - the necessary ground provided was a copper stake pounded into the earth.
Mark, I can't find any reference to BETS-1 changing for AM here in Canada. Can you provide a link or reference?
lt was RSS-210 that had an amendment, posted this a while back. http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01320.html
RSS-210 has both, the 3 meter, 100mW rule and the 250uV/M@30 meters and BETS-1 has just the 250uV/M@30 meters where before RSS-210 had one and BETS-1 had the other.
Mark