This site will plot you out a google map showing the coverage area of your FM broadcast... lrcov.crc.ca/main/
You have to register first, but it's free and I had no issues. The parameters are fairly simple. Most of them are already filled in for you.
The important ones you need is latitude and longitude which can be found by using google earth and placing a placemark on your antenna location. It says the coords in there. There are other ways to find your coordinates also. You need the height above ground which I believe should be 0.5 unless you live on a hill. Power and antenna gain over isotropic. For a dipole this would be 2.14. J-Pole you could probably figure the same, or possibly 2.4 for gain. Antenna height above ground is obviously important.
You then set your TX location on the map. You have to zoom out and zoom back in to where you live and click to select where your antenna is. The receive location is set via a rectangle box area for how much coverage area you want to survey.
It's a neat little tool. Includes terrain like hills and valleys. I made a few coverage maps for my listeners and they seem to be very close to accurate for the average radio. I have however reminded my listeners that this is just a guide to reception and not a tell all.
Should also mention that it was kind of disappointing to me that I am on the skirts of my town and use an omnidirectional J-Pole antenna only to find that the map shows that more of my signal is going out towards the corn fields than towards my town. Sometimes the truth hurts, but the reality is that being on the skirt of my town I am at a lower above average terrain than the rest of the town, so naturally I am working against that. This showed me that a directional antenna couldn't hurt for future thought, but really what I am currently running seems to be providing plenty of coverage for my whole town.
So the moral of the story, don't let the map discourage you if it doesn't look pretty on paper so to speak.
I would just be careful as that neat little tool may serve two purposes...one of which obviously won't be advertised, but quite helpful to enemies of spectrum freedom to aid in locating.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1