If this has been proposed before, please forgive me; I'm a newcomer to the forum.
There's been a fair amount of talk here and probably other places about petitioning the FCC to allow for higher power (1 watt or more) for Part 15 AM stations.
Here's a thought: Instead of that, why couldn't we go after the Commission to keep the 100mw limit, but allow for, say, 50 feet combined antenna/ground lead length? The very legitimate justifiable argument would be that many Part 15 AM's need to be mounted on roofs, second story balconies, etc., and that current regulations do not allow for a *safe* ground in those common circumstances. It is truly a safety issue.
The new 50 foot maximum would provide us operators with a proper ground, while additionally extending our coverages.
And for those whose antennas are indoors only, they would win, too, as they could use a 50 foot antenna, even if they had no ground.
And... as an added bonus... we wouldn't have to replace our existing transmitters.
Seems to me that this type of proposal would get less pushback from the Commission, existing licensed broadcasters, and next-door neighbors... as it doesn't involve a power increase per se.
Has this already been hashed out and chewed over here? And if not, anyone have any thoughts on something like this?
Mark
I would support such a rule change. It would solve many mechanical problems related to equipment placement and would result in increased range.
As you may know the original FCC intent was to limit the range of the signals from Part 15 intentional radiators for reasons usually thought to be to limit or prevent interference to other radio services. Some also have posted that the intent is to limit "stealing" of audience from licensed broadcasters. For whichever reason the range is intentionally limited.
Though changing the range limiting rules is not likely it is worth discussing. If one doesn't ask then one knows the answer.
Neil
Jeffery Gill had a petition for 1 Watt on AM and something about the size of the antenna and ground lead was mentioned. Since the noise floor has increased in many areas for AM I think we stand a better chance of simply increasing the size of the antenna and ground leads. A 100 mW transmitter could have a 5 mile coverage easily with a decent antenna and ground lead. As far as the present transmitters being able to tune to a 50 Ft piece of wire many transmitters will not tune to it. A modified ATU would be necessary to get the transmitter to tune to a 50 Ft piece of wire. I'd love to be able to legally do that with my Talking house as I'm stuck with an indoor antenna due to the Land Lord.
I've thought of something similar, 100 mw, no antenna/ground restrictions, whatever you could do to have it scale within your budget and needs would be okay. What I think is that most new and unschooled broadcasters wouldn't have the wherewithall to put up the most effective antenna and ground, and would be limited to shorter range.
Rich has shown that the local signal from 100 mw can reach a kilometer, or .62 miles from a full quarterwave broadcast tower and ground, simplifying his calculations, though most stations wouldn't achieve this range. Most people who would find the signal would be within about a mile, give or take, whether city or country. That power is unlikely to skip to other areas or shock someone working on the transmitter.
The hobbyist nature of the service would stay intact with the low power, but would be more useful for small neighborhood stations, and make AM the place to go for real localism in the future, with TIS and neighborhood part 15.
Maybe we should work to expand Jeffery Gill's petition for this.
50-foot antenna would match the rule for long-wave Part 15, which allows 50-foot antennas. One tower for several uses.
If we keep the 100 mW number I'd like it to apply to the output power instead of the power to the input of the final RF amplifier.
It's ackward to explain to people:
PEOPLE: How much power do you have?
PART 15 PERSON: 100 mW, kind of.
PEOPLE: Kind of?
PART 15 PERSON: Well, it's 100 mW to the last RF amplifier but by the time it passes through the loading coil only 4 mW gets to the antenna.
PEOPLE: I had a pet rock once, well, gotta go!
Damn Carl I didn't realize that only 4mW actually got past the loding coil. That is twice what the Whole House FM Transmitter puts out to a rubber duck which is 2mW. That is really sad. Yes they need 100mW out to the antenna.
Thelegacy brought up what I was going to say.....the current transmitters were designed to tune with a 10 ft antenna. To take advantage of the longer length you would need a new transmitter when the manufacturers redesign the current ones. If it were just increasing the power to the final the same thing would be...you'd need a new transmitter made to the new regulations to take advantage.
Always a catch to everything but I support any relaxing of the current rules.
Mark
Or in the case with the iAM or talking house AM Transmitter you could build a modified ATU with the new coils and a linear amp to boot. If the rules were say 1 Watt you could have a linear amp that takes the 92.5 mW that the Talking House (iAM) transmitter puts out and raise it to the new level. If they simply allow more length the new ATU you build will have the new coils that allow the tuning of a 50 foot antenna. This would probably triple your range even at the 92.5 mW that the transmitter puts out. Personally I'd like that AM Stereo transmitter and at that point I'd try and raise the power of that once 1 Watt AM was allowed. But its been months since Jeff started the petition and so far nothing has came of it. I'm still waiting to see what the NAB has to say on that one.
i say we go back to the original part 15 am it was 100mW no ground restricitons. extremely few people are going to be able to install a full 1/4 wave vertical over 120 quarter wave ground radials. generally they get up 100ft max, typically it's 50ft or less and in most cases a less than ideal ground radial set.
so just eliminating the ground restricitons won't really change anything except the nit picking over elevated installs.
rich's own calculations support that. he calculated a full 1/4 wave ground lead ove a full 1/4 wave ground system in an ideal ground condictivity would produce a usable signal of about 150uV out to about 4 miles in a low RF noise environment. this is for an ideal setup and i have yet to see a part 15 am broadcaster with an ideal setup so that 150uV is likely to occur at maybe 2 miles but likely not much more than 1 mile.
most of th extreme ranges that are seen are to a very good car radio setup in a low noise environment.
take TIS for example
it takes 10 Watts at least into a 50ft radiator over a less than ideal ground system to produce a usable signal at 3 miles.
It goes without saying that allowing 30 or 40 extra feet to a Part 15's antenna/ground lead won't increase your coverage by too many multiples. Because let's face it: there's zero chance that the FCC will allow any form of unlicensed operation that could pooch out a usable AM signal to 5 or 10 miles.
I've seen (online) a number of Rangemaster installations with longer-than-legal ground leads. Their signals get out much farther than those who keep it dead legal. And... the Rangemasters *reportedly* tune to that extra length.
It would be interesting to see what kind of distances other Part 15 transmitters would get with longer antenna/ground lead combinations, even if the transmitters would not tune perfectly to the new lengths.
Well, I have a Talkin House, and there you get to choose the wire or 75 ohm out with a switch. The 75 out could connect to a tuner for any kind of antenna then.
It seems to me that keeping the power at .1 watt, but getting rid antenna and ground system restrictions makes the most sense. There's a clear limit on range technically, easy to measure 100 mw input power, and already a power level that's pretty much been proven to cause few problems, as 100 mw has been in place for years.
The Leg acy, Most AM .1 watt systems put out less than 1 milliwatt, according to what I read on an antenna web page some years ago. The guy designed his own cooper pipe and PVC antennas, really an ingenius design how he did it from hardware parts.
He was working to get even over 1 milliwatt to the radiating section of the antenna, and the idea was that the loading coil was acting as a choke on the antenna lead, but was required to be there anyway, because matching was something like 1000 times more effective with the 'choke" in place.
... I didn't realize that only 4mW actually got past the loading coil. ...
Below is an analysis of a Part 15 AM system using ~ typical values for the resistance of the loading coil and r-f ground connection, and 50 mW of output power from the transmitter.
The power flowing from the loading coil into the base of the 3-m radiator is about 0.08 mW.
Rich's analysis illustrates why the radiated power is so low. The model usually used to describe and analyze a short base coil loaded antenna system is a series circuit consisting of the coil inductance, the coil RF resistance, the radiator capacitance, the ground resistance, and the radiation resistance. At resonance, the inductance and capacitance cancel leaving the coil RF resistance, the ground resistance, and the radiation resistance in series. It is the relatively very small value of the radiation resistance which results in the very low efficiency of the system.
The radiation resistance is set by the physical parameters of the antenna, primarily the radiator length. Since this is regulated by Part 15.219 we have no effective control over this and can only do things to reduce as much as possible the coil RF resistance and the ground resistance. Rich's analysis uses typical values for these resistances and further improvement is not going to increase the efficiency much.
Allowing longer antenna length which will increase the radiation resistance can greatly improve this efficiency and would be the simplest way to get more range.
Neil