Part 15 FM...

[radioman148]

Signal strength decreases logarithmically as a function of the distance. So if your transmitter/antenna has a maximum 500 foot range, and you placed the tx/antenna combination on a 1000 foot tall building, you wouldn't hear it on the ground!

FM Doesnt Work That Way Stormy.
Line Of Sight Remember. Putting it up higher would only
increase its range. a Transmitter normally only going 500 FT and put it on
a 1000 ft pole you would get the station very clear for maybe a mile or so.

Its Amazing really.

So in other words if I connect a part 15 transmitter to an FM antenna at 60 ft I'll get out at least several blocks.

[R. Fry]

So in other words if I connect a part 15 transmitter to an FM antenna at 60 ft I'll get out at least several blocks.

The link below leads to a chart showing signal strength vs. distance for an FCC-compliant Part 15 system (the red trace) and several other systems. These are based on a free-space, unobstructed path.

The power radiated by a 1/2-wave dipole to produce the maximum field allowed by Part 15 FM is very small:  0.000 000 01143 watts, or 11.43 nanowatts.  Most "Part 15" FM transmitters produce thousands of times this amount of power.

The signal from a compliant system drops below 10 microvolts/meter at a distance of around 60 meters, or ~ 200 feet.

So legally serving a radius of several blocks is unlikely, regardless of the height of the transmit antenna (unfortunately).

http://i62.photobucket.com/albums/h85/rfry-100/6417f684.gif

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[radioman148]

So in other words if I connect a part 15 transmitter to an FM antenna at 60 ft I'll get out at least several blocks.

The link below leads to a chart showing signal strength vs. distance for an FCC-compliant Part 15 system (the red trace) and several other systems. These are based on a free-space, unobstructed path.

The power radiated by a 1/2-wave dipole to produce the maximum field allowed by Part 15 FM is very small:  0.000 000 01143 watts, or 11.43 nanowatts.  Most "Part 15" FM transmitters produce thousands of times this amount of power.

The signal from a compliant system drops below 10 microvolts/meter at a distance of around 60 meters, or ~ 200 feet.

So legally serving a radius of several blocks is unlikely, regardless of the height of the transmit antenna (unfortunately).

http://i62.photobucket.com/albums/h85/rfry-100/6417f684.gif

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That's kind of what I figured. Thanks for the confirmation.

[stormy01]

Signal strength decreases logarithmically as a function of the distance. So if your transmitter/antenna has a maximum 500 foot range, and you placed the tx/antenna combination on a 1000 foot tall building, you wouldn't hear it on the ground!

FM Doesnt Work That Way Stormy.
Line Of Sight Remember. Putting it up higher would only
increase its range. a Transmitter normally only going 500 FT and put it on
a 1000 ft pole you would get the station very clear for maybe a mile or so.

Its Amazing really.

I believe that almost no one is really reading what I am really saying here! (Many of you have a pipe dream that your neighborhood is gonna discover your little 25mW FM transmitter and listen on in - yeah, if you tell them it's there on the dial).

Again, even if the signal completely disappears at 500 feet and its Light Of Sight at 500', someone like Richard Fry, please explain to us how on earth you're gonna a hear station more than 10 times the distance away at about a mile (5283') also LOS when it was already completely gone [not receivable by the radio tuner] at 500'...something is wrong here...either you have more than the legal power for a Part 15 FM device and/or your antenna has gain which produces a signal whose field strength greater than the legal limit! 

                                      If you can't hear a signal that no longer exists at a lesser distance, then in turn at a greater distance given
                                           that there were no obstructions at either distance,you are not going to be able to hear the signal either!

                                                                 You can't get a signal out of nothing! It has to be there!

[R. Fry]

(Many of you have a pipe dream that your neighborhood is gonna discover your little 25mW FM transmitter and listen on in - yeah, if you tell them it's there on the dial).

However that 25 mW FM transmitter with even a very simple whip antenna can produce fields far in excess of those allowed by Part 15 FM.   Many of the NOUOs (violations) listed on the FCC's website refer to measured fields produced by radiated powers of about this value.

For example, the 25 mW curve in the chart I posted shows about 700 microvolts/meter at 1.61 km (one mile).  That is a fairly strong signal that could be listened to on almost any FM radio, including a Walkman.  But it is also illegal at that distance for a Part 15 FM station.

Again, even if the signal completely disappears at 500 feet and its Light Of Sight at 500', someone like Richard Fry, please explain to us how on earth you're gonna a hear station more than 10 times the distance away at about a mile (5283') also LOS when it was already completely gone [not receivable by the radio tuner] at 500'

When LOS propagation loss causes the signal to fall below the acceptable noise threshold of a given receiving system then moving it further from the transmitter does not improve the signal - it is reduced even further.

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[stormy01]

However that 25 mW FM transmitter with even a very simple whip antenna can produce fields far in excess of those allowed by Part 15 FM.   Many of the NOUOs (violations) listed on the FCC's website refer to measured fields produced by radiated powers of about this value.

For example, the 25 mW curve in the chart I posted shows about 700 microvolts/meter at 1.61 km (one mile).  That is a fairly strong signal that could be listened to on almost any FM radio, including a Walkman.  But it is also illegal at that distance for a Part 15 FM station.

Mr. Fry just wants to protect you guys from a NAL...unless you don't mind parting with $10,000.00 of your ca$h should you get caught by the FCC... If all of you really want to do over the air radio right, get your investors together and buy an existing station or build a new one. Part 15 is meant to be "yardcasting" - it's a convenience so that you can listen to your music on your property without moving your component stereo system outdoors... Instead you can listen out on the patio with a boombox or on a "walkman" while you mow the lawn... Have a nice weekend....

[LibertyNT]

Signal strength decreases logarithmically as a function of the distance. So if your transmitter/antenna has a maximum 500 foot range, and you placed the tx/antenna combination on a 1000 foot tall building, you wouldn't hear it on the ground!

FM Doesnt Work That Way Stormy.
Line Of Sight Remember. Putting it up higher would only
increase its range. a Transmitter normally only going 500 FT and put it on
a 1000 ft pole you would get the station very clear for maybe a mile or so.

Its Amazing really.

So in other words if I connect a part 15 transmitter to an FM antenna at 60 ft I'll get out at least several blocks.

Yup. Although i Doubt it would be legal. Your Best bet would be going AM.

[Nostalgia]

I was discussing quality (FM) vs distance (AM) with someone wanting to put up a part 15 distributed system covering several miles of a local community.  He asked me about my system.  Allow me to quote myself in my reply to him:

"Most, like you, opt for AM to get the distance.  I wanted quality so mine is FM.  FM has even more antenna restrictions than AM so unfortunately it has less commercial appeal for ventures like yours even though it is in stereo and sounds better.  I am happy with the extended neighborhood coverage I have.  It is only meant to allow me to hear my own website through FM radios throughout the house and yard, all beyond that is ego!"  (emphasis added)

It is fun to hear my station as I turn onto my street but I'm sure I am the only one listening!  Stormy01, as well as others, have made some good points but as part 15 goes, it is what it is, and that is hobby radio.  True, some are making a commercial venture out of it, and some appear to actually be making a go of it but those are rare.   I had an offer in on a small AM last year but the seller backed out at the last minute.  The whole market has been turned upside down since then so perhaps it was a blessing he got sellers remorse but I will continue to be on the lookout for a "real" radio station.  Meanwhile my little FM100B is playing oldies in the background as I type this.

[R. Fry]

Mr. Fry just wants to protect you guys from a NAL...unless you don't mind parting with $10,000.00 of your ca$h should you get caught by the FCC...

Thanks, but a review of this subject on the FCC website shows that normally they first issue a Notice Of Unlicensed Operation (NOUO) to the operator of an unlicensed "station" that is non-compliant with Part 15.

That FCC NOUO by itself does not require a monetary fine.

Further FCC actions/sanctions depend on the response(s) of the person(s) receiving the original NOUO.

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[stormy01]

Mr. Fry just wants to protect you guys from a NAL...unless you don't mind parting with $10,000.00 of your ca$h should you get caught by the FCC...

Thanks, but a review of this subject on the FCC website shows that normally they first issue a Notice Of Unlicensed Operation (NOUO) to the operator of an unlicensed "station" that is non-compliant with Part 15.

That FCC NOUO by itself does not require a monetary fine.

Further FCC actions/sanctions depend on the response(s) of the person(s) receiving the original NOUO.

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Thanks for the clarification. There are some individuals out there that need to be aware and do the right thing from the get-go, instead of seeing what they can get away with, pushing the envelope (and I don't mean the modulation envelope, either...