How Much Power 'Til the FCC Busts Ya?

[henry]

Anyone have any experience with their Part 15 signal? I know i'm using a really weak transmitter on 99.9 ... and I only get about 30 feet and it's extremely line of sight.

I'd love to boost it up but I don't know how much I can do (and what the penalties are) if I get busted.

Is 25mW too much? 250mw?

If so, do they send me a warning so I can shut it off if it causes problems, or would they raid my stuff?

If it's the latter, I won't do it - but I'd happily comply if someone simply complains and tells me to shut down.

Anyone have any experience?

[CAwasinNJ]

I don't have experience with such matters, but wattage isn't the determining factor. It's actually calculated in volts per meter (essentially signal strength), because you have to consider the efficiency of the antenna. In the FM broadcast band, I think the limit is 150 microvolts/meter at 3 meters, and it can't interfere with a licensed station. If you want some gory details, here's a PDF from the FCC.

www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Ok, that's the legal stuff. As for how far you can push it before anyone notices, that's a whole different ballgame. I'm actually quite surprised at how far unmodified commercial part15 transmitters can get out. What are you looking to do with it? That will probably point the help in the right direction.

Rather than upping the power, you could also look at a series of low power stations over a given area and setting them up translator style. You can start at 99.9 in a central location, then rebroadcast that on another frequency (say 93.7 in the Salt Lake area) near the fringe of the coverage of the "primary" then further out rebroadcast the rebroadcaster back on 99.9 etc. Making sure you don't end up with feedback is a little tricky though. Another idea would be to use a high power transmitter in one of the free bands (unlicensed with virtually unlimited power) and then rebroadcast that on various low power transmitters in the target areas. There are definitely possibilities.

[henry]

I'm trying to cover a small apartment complex. Right now I can get it well all over my unit ... in some rooms of adjoining units ... and of course, in a car in the parking lot right in front of the window.

But I tried to promote the station to other friends in the complex and they all say "I can't get it." I'd like to get it powerful enough they could set alarm clocks to it.

My worry is enforcement. Let's say I used a 1W transmitter (probably wouldn't). Do they usually send a warning first, or do they fine/raid fairly quickly?

[CAwasinNJ]

Anecdotally, it depends on who complains.

If you were looking to be that powerful, I'd probably drop below the bottom of the FM dial down to ch 6 territory (87.5-87.7 or so). You have to watch out for spurs though. My car transmitter on 99.9 interferes with 103.9 somewhat in the car. With higher power it could start messing with someone trying to listen nearby. And if you start messing with public safety or air frequencies at any sort of power, the Feds will drop the proverbial anvil on your head. They have no tolerance for that, and I don't blame them at all. the whole thing is a little dicey.

There's another possibility though. Since a building is probably all fed from a main power line, what about carrier current AM? You're talking about a clock radio, so the fidelity is probably already going to be lousy. It just might work, and I think the power levels can be higher since it's a closed system.

[friendlee]

I do part 15 AM and with the 'Cadillac' of rigs (Hamilton Rangemaster) I get about a mile; certified under 15.219 - three meter antenna and ground lead. Part 15 FM is usually certified under 15.209 which limits the field strength giving about 90-150 foot range. Carrier current AM is getting pretty difficult with so many consumer devices these days using switching power supplies (read noise!)

[henry]

Thanks for the info. I really would like to keep it on FM. I'm using a software audio processor that sounds really good, and I love how it comes booming inside the house ... but it likes to drift to 99.8 or 100.0 - which is totally useless on most digital radios.

I'm thinking of buying a Ramsey FM100 kit, or maybe the FM30 ... it's PLL, but I don't know if the power output is gonna be any better, or worse than my ol' Canakit rig. But I don't want it to get too powerful that I find a bunch of agents raiding my place.

[CAwasinNJ]

Friend, do you happen to know if there's a power limit on carrier current?

[friendlee]

I'm not sure about the power limit but the injection point has to be below the step down or service transformer so it stays "contained" to the building you intend to broadcast to. Example: the college radio kids want to transmit to the dorms. They have to keep their signal confined to campus proper and for that matter, only portions of campus. To do this, each dorm would have a transmitter tied to the secondary side of the building transformer. It would not be in good form to inject above the transformer and service all the dorms from one unit as this could over radiate into adjacent buildings or neighborhoods off campus and result in a spanking by the commission.

I'm sure there are limits/boundaries in place somewhere in Part 15 probably in the low .200's (since most all broadcast applications are covered in the .200 to .225 range). I'd be willing to bet that if you can hear a carrier current station in your toaster coils it is probably running a little hot (the station, not the toaster). ;D