I continue to read elsewhere sweeping statements that a legal Part 15 statement will not leave your own property. Of course, there's no accompanying math or physics to prop up those statements at all. That's because there are none possible. Perhaps those who continue to put this msinformation forward believe that if they continue to say it, eventually it will become like fact.
But the truth is that the range of a Part 15 signal is entirely dependent on the receiving equipment and obstructions between the receiving and transmitting antennas.
My recent research on receiver sensitivity revealed that there are any number of car receivers that are capable of receiving signals in the 1-1.5uv range with up to 20db quieting. A Part 15 legal signal with field strength of 250uv/m at 3 meters has a field strength of 5uv at 150 meters (around 500 feet) line of sight, more than strong enough to be heard by those car receivers. And for some, that range could extend out to 800 feet or more, line of sight.
There's also no doubt that the typical portable or handheld FM radio has a much more difficult time hearing a Part 15 legal signal. That same research showed that the typical portable might hear a signal out to about 40-45 meters (around 150 feet) and a typical handheld would be lucky to hear it at 20 meters (maybe 75 feet).
So while it is true that portable and handheld receivers might not hear a Part 15 legal signal 'off your property' (depending on the property size, of course), a good car radio or the best home stereo receivers (other research has showed that they have pretty much the same sensitivity as car receivers) could hear it much, much farther.
QED.
What Artisan says seems obvious on its face and soundly reasoned, and there's potentially yet another variable which might apply in some circumstances that further contradicts the claims being cited.
The boundries of "your own property" might flex, as when purchasing lots on several sides.
Although there might be some kind of an average lot size for a parcel of property, there are so many possible exceptions given apartments, retirement centers, large ranches, etc., that using "your property" as a measure in Part 15 compliance is absurd.
Artisan says "Of course, there's no accompanying math or physics to prop up those statements at all," and that fact serves to nullify the claim "I continue to read elsewhere sweeping statements that a legal Part 15 statement will not leave your own property."
Therefore the source authors of the claims being debunked by Artisan are not only wrong, but foolish.
Just to make sure the maze of logic here posted is not misunderstood, I am 100% agreeing with Artisan and denounceing the false claims and misinformation being referred to.
Thank you, ArtisanRadio, for the clear and reasoned data based presentation.
Over the years I have engineered several communications systems: wired, radio, and optical. Ultimately, it is the signal to noise ratio at the receiver which dictates the quality of the communication. For FM BCB radio the major source of noise is the receiver itself and that is why the sensitivity specs. often refer to "dB of quieting". What is being "quieted" is the receiver noise. (This is not the case for AM BCB.)
Simplistically, the ways to improve the signal to noise ratio are to increase the transmitted power, decrease path loss, improve the signal at the receiver by use of a good antenna, and improve the noise performance of the receiver electronics which amounts to sensitivity.
As Part 15 hobbyists we have no control over the transmitted power since it is limited by the rules. We have some but limited control over path loss by appropriate positioning of the transmit antenna. We only control the receiver antenna and specifications if it is our own equipment but lack such when considering a potential listener.
A serious ham or SWL will give due consideration to the receiving equipment and if I were interested in the programming of a nearby Part 15 station I would do likewise for the band of interest, however the average listener probably won't. This is a limitation we need to acknowledge.
For reasons cited by myself and by ArtisanRadio it is silly to try to define "legal range" based only on distance or property boundaries. It is not silly to do as ArtisanRadio has done which is to give range estimates based on known path and receiver specifications. I have observed that the range of my FM transmitter is in line with what he stated, being short range for portables and long range for car receivers.
i figure if i were to mess with pt.15 FM, i'd play dumb on pretty much like...everything and maybe i would have to ask for forgiveness, which in the USA, is way better than asking for permission.
A while back I posted a link to a page that can do LR modeling of signals, see thread http://www.part15.us/forum/part15-forums/transmitter-talk/modeled-part-15-fm-service-contour-map-generation .
Height does not help for getting a large 60dBu service area, but height does help push out where a car radio will receive the signal. A clear LOS 800’ service radius on a channel without co or adjacent interference is possible into a car radio with the transmitter 30’ to 50’ in the air.
... But the truth is that the range of a Part 15 (FM) signal is entirely dependent on the receiving equipment and obstructions between the receiving and transmitting antennas. ...
If the above quote is true, wouldn't it mean that the field intensity arriving at an FM receive antenna has NO dependence on the ERP of the transmit system toward that receive antenna?
Nit picking. I probably should have said that the range of a Part 15 (FM) signal with a given field strength is entirely dependent ...
But that was certainly the point of the rest of the post, and I don't think that anyone reading that post would have missed it.
By saying "the range of a Part 15 (FM) signal" you automatically refer to a given signal strength, namely, a Part 15 (FM) signal strength.
Artisan fell for a classic red herring.
I knew I was right that on certain Radios you can legally get 1/4 Mile on FM. I think missinfo was given on purpose mostly by anti FM trolls. Though the DainSonic AX-05B might be heard 1/4 mile in a car does not automatically mean your illegal. FM part 15 operators have been persecuted for too long. Let the light finally shine.
1/4 mile is over 1300 feet, or 400 meters. At 300 meters (or about 1000 feet), the field strength of a Part 15 legal FM signal is 2.5uv, just about at the limits for reception of a car or home stereo receiver that has a sensitivity of 1uv.
I suppose it's possible that with an exceptional receiver (some of the car receivers in that study out of the Netherlands did have measured sensitivity of well under 1uv), and an exceptional antenna, you might be able to pick up something of that signal at 400 meters. But I don't think that it will be listenable.
This discussion about Part 15 FM is being noticed. I just read a repeat of my analysis over at another website (you can probably guess what it is), including looking at receiver sensitivity (well, well). The conclusions were slightly different, but at least they've backed away from arm waving and general statements, and admit that it is possible for a Part 15 FM legal signal to travel up to 300 meters. Quite a bit different than the 200 feet (or 60 meters) that was being bandied about earlier. That, I at least welcome, but I have to wonder if they'll ever acknowledge the work done here (and elsewhere).
All that just strengthens my position that depending on your application, the target receivers, the location of your transmitting antenna and a whole host of other factors, Part 15 FM can be a lot more useable than they have previously indicated.
I didn't take a tape measure and the house was pure wood. Now too FM can Bounce too off of buildings like a rubber ball. That sometimes can boost a signal. The harder you throw a rubber ball the harder it bounces back. There was a house not too far from me and there is an open area between the houses. Multipath can happen and if done just right you can make an FM signal go further by bouncing it off of something else. That is how a satellite dish works.
I'm glad maybe we could have the anti FM trolls to stop their trolling and trying to rat off all FM Micro broadcasters. Unless they are really raising cain don't troll on them. Just like that AM station that was talked about earlier that had a 40 foot antenna Hey it may be Over but We are not the FCC and as they say in church don't complain about a speck in your neighbors eye when you have a board in your own eye. Lets just worry about getting the range legally on AM AND FM to be 1 Mile at least. You really don't need more than 1 mile on FM to have a good time.
There is nothing bad about using an FM transmitter that does not excede the limits listed in 15.239. There are some issues to watch out for:
1. the listeners recieve equipment and acceptable noise dictates the recieve range.
2. licensed services can take your channel and even if it is the only good channel there is nothing you can do about it.
3. some of the better radios to listen to your part 15 signal are car radios but car radios will not be in range for long.
So part 15 FM is largely "build it and hope they come".
If you are near town houses, restaurants, places people travel and they happen to stumble upon your station and like it they'll listen and see what you play. If you also stream on the Internet its a great way to promote your world wide Internet stream. I do this with my station.
Ever thought about why we want attention?
Sure, we want to broadcast on the radio and have people pay attention to what we say and do.
What about them? What do they think? What do they like? Maybe they should broadcast to us? Would we listen to them? I wouldn't.
Just do what I do... eliminate the middle man... broadcast to yourself! You might like your station and sit there like I do holding a portable radio and admiring the crisp, clear sound of (insert your call letters here).
You will never be disappointed if you like what you do on the air and actually get to hear it!
LOL. Carl, that's probably why a lot of people start with Part 15 in the first place. Listeners come as an after thought, or just good fortune.
My Part 15 station on Bowen Island in Canada was initially conceived to broadcast to cars in and around the area of my bookstore. But because we were located at the top of a hill, the ferry car lineup at the bottom was also within range, and it eventually became the primary target listening audience.
I also had people come into the store and tell me that they would drive over from where they lived and park just to listen to the station.
You don't always have to be concerned about how long a car will be within range.
Radio is not dead!