"If you're running a Part 15 legal AM station and only getting out 200 feet you might want to check and make sure your transmitter is plugged in, or you've connected your antenna."
A possible exception for unlicensed AM operators subject to FCC rules might apply to those operating (strictly) under §15.209 -- depending on the performance of the receiver, and the local r-f noise level on the transmit frequency.
I saw where a FCC Engineer testified under oath that the typical range of a Part 15 FM was a bit over 1,000 feet.
Where the HECK do people keep coming up with this 200 foot range BS?
This 200 foot notion comes from a Public Notice published by the FCC which states that Part 15 AM and FM transmitters produce a typical range of 200 feet. It was not presented as a rule but rather as an example of what to expect. The receiver used was not specified so this is certainly not scientific.
Here's a link to one such document:
http://www.fcc.gov/ftp/Bureaus/Mass_Media/Databases/documents_collection/pn910724.pdf
Neil
Now that you mention it I DO remember that FCC posting about typical range, and while that's probably true for an FM, it's certainly not for an AM. And again "typical".
Just like the agent testifying that that "typical range" is 1000 feet. That's like swearing under oath that you don't really know.
My blatantly legal AM goes over a mile as the crow flies every single day. Not "under good conditions" but every day. I have the advantage of being very rural with practically no AM noise, no real interference being generated, and no big buildings. My onnly interference is at night when KZON comes blasting in on skip. Oddly, with these cold winter nights recently I've been able to listen to my signal at night nearly as good as during the day.
I suppose you'd have limited range on AM under the field strength rule, rather than the power/antenna rule (I get the FCC number rules mixed up) but still you'd be well over 200 feet I'd imagine. Maybe "typically" people put up badly assembled stations? I often wonder how they came up with that AM field strength rule because a properly installed, fully legal 100mw, legal antenna, no ground transmitter does a hell of a lot better than the limit spelled out in 209 at 30 meters.
Tim in Bovey
There are a lot of misperceptions 'out there' about Part 15 radio. I don't know whether it's a misperception of the rules or just general laziness when it comes to finding out what is truly legal.
I can't count the number of times that someone has mis-stated that the legal power limit for Part 15 FM is 100 milliwatts, obviously confusing AM and FM.
And then here in Canada, there's this doozy. The regulators here make a distinction between unlicensed broadcasting, and everything else. The rules that govern the everything else on AM are contained in a document entitled RSS-210, which is pretty much identical to Part 15 (you're allowed either a maximum field strength or a 3 meter antenna/ground combination and 100mw input to the final stage of your transmitter). But the rules for unlicensed AM broadcasting are contained within the BETS circulars - and there is no 100mw output option for AM, just a maximum field strength of 250uv/m at 30 meters. Which, ironically considering this discussion, will likely get you not much more than 200 feet distance.
IF you know a link to that "Testimony under oath" where an FCC person stated "1,000-feet for typical Part 15 FM" it would be worthwhile having a copy of that printed and saved in our Inspection Folder.
In the meantime, we can print your reference to it and use that.
I would think that a well kept "Inspection Folder" kept at our transmitter would make a very strong talking point if an inspector arrived.
"... a properly installed, fully legal 100mw, legal antenna, no ground transmitter does a hell of a lot better than the limit spelled out in 209 at 30 meters"
The reason for such a belief probably is related to this:
Except for the "no ground" phrase quoted above, and, after FCC §15.219 was added to the Rules,
1) some proponents decided/promoted that the "ground lead" defined in FCC §15.219(b) did not include the entire length of the conducting path from the r-f ground terminal of the transmitter to a true r-f ground, and
2) the use of "loading coils" was introduced and used by such proponents to resonate the radiating length of whatever antenna system conductors were used in that system, thus greatly improving the radiated fields they could produce with respect to FCC §15.209.
Prior to FCC §15.219, the unlicensed transmitter power and antenna system used were unimportant as long as that combination met FCC §15.209.
According to highly credible sources within the FCC, the original unlicensed field at 30 meters permitted by FCC §15.209 in the AM broadcast band under the current numbering sequence, and the field expected at 30 meters under the present FCC §15.219 were expected by the FCC to be ~ equal.
I should really write stuff down.
Last fall I took field strength readings from my station at 30 meters. It was considerably more than .209 mentions. If I recall, for my frequency the limit was 14.81 uV. I do believe I wrote it down on a hunk of scratch paper, but didn't keep track of it.
I have a closed gas station at the end of my block and I measured exactly 30 meters from my antenna and wound up just past the island of gas pumps. At this spot I have a straight line view to my transmitter antenna -- no obstructions at all -- perfect to determine exact field strength. Actually, I guess, it's a tad more than 30 meters as I measured from the spot directly under my transmitter to the test spot -- but my transmitter is 3 stories from the ground, so with the angled line from antenna to the test spot it's a tad over 30 meters.
We're supposed to get temps in the 30's this weekend -- maybe I'll stop and take another reading. However, I do notice that no one, near as I can tell, has ever posted their actual field strength readings on this site -- maybe because so few are equipped to take the readings in the first place, but perhaps it's not wise to do so?
Tim in Bovey
"... However, I do notice that no one, near as I can tell, has ever posted their actual field strength readings on this site ... "
Probably true as far as applies to the posts here on Part15.us, and on other "hobby" websites by proponents/operators of unlicensed systems using the AM broadcast band.
But IIRC, the FCC has issued citations (NOUOs) to unlicensed operators when they have found that the fields produced by such systems exceeded those permitted for that frequency under §15.209, and on finding by further inspection that those systems also were non-compliant with §15.219 -- even referring in such NOUOs to the excess length of the "ground" conductor that was used.
Tim, I suspect the reason no one has posted field strength readings is that you have to be compliant with either 209 OR 219 - not both. Most will attempt to be compliant with the latter, which does not require a known field strength (but which has a huge gray component in the area of ground leads, unless, as in your case, you don't have one).