Just for kicks I attached a diploe TV/ FM antenna to my Ramsey FM10C and it is getting out quite a ways. Rough estimate is in excess of 1000 ft on a car radio (2012 Ford Fiesta)that is not that great on reception.
The antenna and transmitter are indoors running sound from Itunes on a PC. The co-ax cable from the transmitter to the antenna is less than 1 meter and each pole of the antennna is fully extended to 84 cm. each with no ground. Nothing else is connected.
Thanks,
Chance
Probably, but at 1000 feet who cares? Make sure you are stepping on a licensed station and not splattering on the co-channels. Be a good neighbor.
I find your setup to be reasonably close to compliance and approve of it.
Moderately sure I am not stepping on a licensed station 102.7 is clear here. Pretty sure I'm not stepping on adjacent channels, but I hve nothing but portable radios and automobile to monitor. I really do not want a visit from THE MAN.
Thanks,
Chance
Your antenna being indoors probably helps keep the distance down (I suspect that if it was outdoors mounted high you'd get more range).
That being said, I use the standard of 600-800 feet for car radios (using U.S. rules). You're getting out a bit more than that (25-30% more, so your field strength is probably around 325uv/m @ 3 meters). Would that be enough for an FCC inspector to be concerned? Only the particular inspector would know, but most violations are for field strengths a lot more than that.
To be safe, you should probably take it down to a maximum range of 800 feet. Adding some length to the coax (so that you get signal losses) might do the trick.
I'm sorry, I'm a newbie. Would you be so kind as to explain what 325uv/m@3 meter means and why I should be concerned?
Chance
Part 15 FM is governed by field strength. The maximum allowed by the rules is 250uv/m @ 3 meters (that's 250 micro-volts as measured by a one meter antenna at a distance of 3 meters from your transmitting antenna). That generally translates into 150-200 feet range to an ordinary consumer table top type radio up to 600-800 feet to a good car radio. That's how I approximated your field strength - it's likely over the limit, but not by much and whether an FCC inspector would consider it a violation is unknown.
That's why I suggested one way to bring down the field strength a bit. Another would be to play around with the dipole antenna (bending it, etc.) so that you can reduce your range to about 800 feet to that car radio maximum. Or move the dipole to another location in your house, one that might have to go through a few more obstructions to get the signal outside (the FCC will measure your field strength, if they do it at all, from outside your house).
The FCC rules Part 15.239 limit the signal from such a transmitter and antenna to less than 250uV/meter at 3 meters. The field strength of a signal is a measure of how strong the signal is and thus how far it can be heard.
Since almost all of us using the FM band are not able to measure the field strength the best we can do is go by the FCC's estimate that a compliant transmitter and antenna will produce a range of about 200 feet. The problem is that they do not specify what kind of receiver is used fir this check. Common experience is that car radios give better range than table top or portables and a range greater than 200 feet may be legal with a car radio. Such a range doesn't mean you are operating illegally but doesn't guarantee that you are not.
The only way to be sure is to purchase and use a FCC certified transmitter but this doesn't mean that a non-certified transmitter is not legal to use.
From the numbers you gave your system is operating near or slightly above the legal strength limit.
Often transmitters are sold with a stated power rating which is not regulated by the FCC so this can cause confusion. There is no power limit which will guarantee the legal field strength will not be exceeded.
With all that being said, I operate on FM with a transmitter where I have adjusted the antenna length to give a range of about 200 feet on a portable and this is the best I can do in terms of being compliant. There are many of us doing the same thing without being visited by the FCC.
Most of the published citations report transmitters operating grossly over the field strength limit but I recall a few which were above the limit by a factor of 5 or so. If you keep your range as it is you should be at low risk but this is not guaranteed.
Neil
You guys are the best.
To be sure I was blown away by the reception, but then began to think about the rules. Make no mistake I want to be in full compliance.
Thanks for all the advice, etc.
Part 15 is awesome. Long live part 15.
Chance