legal distance for a big fm station to transmit

[james campbell]

I was driving home and was looking for something to listen to on the radio,nothing good until I found one on my last preset. Then I realized that it was my fm station for my show:shock:. I did some looking and it is a station 260 miles away. By the time I get home its gone. So is it legal to transmit that far?

[DougP]

you can not transmit that far but a legal station can.

[Steven]

The rules say explicitly that if you interfere with anyone's reception of the licensed FM station, then you are required to stop transmitting.

If you can't hear that station when you get home, then the chances are good that you won't interfere with it.

[Guest wbottomley]

james campbell wrote:

I was driving home and was looking for something to listen to on the radio,nothing good until I found one on my last preset. Then I realized that it was my fm station for my show:shock:. I did some looking and it is a station 260 miles away. By the time I get home its gone. So is it legal to transmit that far?

The distance an FM station can transmit depends on the type of license they have. Class A - B - C - Low Power, etc.

Here in the South, we have 100KW stations but I know of a couple of grandfathered 250KW stations.

[PMC]

ya knew I was going to say something

it's called Tropospheric Propagation or Tropospheric Ducting

On frequencies above 30 MHz, it is found that the troposphere has an increasing effect on radio signals. The radio signals are able to travel over greater distances than would be suggested by line of sight calculations. At times conditions change and radio signals may be detected over distances of 500 or even 1000 miles and more. This is normally by a form of tropospheric enhancement, often called "tropo" for short. At times signals may even be trapped in an elevated duct in a form of radio signal propagation known as tropospheric ducting. This can disrupt many radio stations on the FM dial because interference may be encountered that is not normally there.

I was working for WDVE in Pittsburgh many decades ago and as I was driving home when I got to the 70 dBu range of my station I heard my station slowly fade away then this "beautiful Music" station was getting louder and louder it was the WAVE on 102.5 in Tampa Florida and it was tropospheric ducting that made it happen, the best time to catch these "waves" is when its really hot and humid over a large part of the USA.

[james campbell]

Steven wrote:

The rules say explicitly that if you interfere with anyone's reception of the licensed FM station, then you are required to stop transmitting.

If you can't hear that station when you get home, then the chances are good that you won't interfere with it.

Thanks for all the good info. Yes by the time I get home it is a bunch of other stations overlapping.I get farther south away from the signal. I just hope it don't strengthen when the leaves fall off this winter

[Guest guest]

Okay the million dollar questions are {Since James brought this up}:

I Hope our FCC knowledgable folks can answer these, as I'm sure others may be thinking/asking the same thing. Max-Paul?


Q1. If there is a LICENSED STATION that can be picked up from time to time "CLEARLY" in your area that is over 75-100+ miles away, and that happens to be the same Frequency you use to transmit your show on, does that by the FCC's rules and regulations constitute interference with a/that licensed station?

Q2. So is there any defined area {mileage} away from an licensed station that the FCC would not view this as interference from YOUR low power FM transmitter that may happen to be on that same Frequency?

Q3. Also, if you can pick up a station on the Frequency you use, but that station is always overly static, distorted and broken up, never has a clear signal, but still within hearing, but badly, can you transmit on that Frequency? {I ask this because there is a station like this on the frequency I use, never heard any call letters to date, so could be a distant transmitter or an unlicensed station, but if it's a licensed distant station and it is never clear, can that frequency be used?}

Thanks for any relevant answers to these questions in advance from our FCC knowledgable folks here.

Just want to keep myself within all legal limits whenever possible and as much as possible!

[Torqumada286]

PMC wrote:

ya knew I was going to say something

it's called Tropospheric Propagation or Tropospheric Ducting

On frequencies above 30 MHz, it is found that the troposphere has an increasing effect on radio signals. The radio signals are able to travel over greater distances than would be suggested by line of sight calculations. At times conditions change and radio signals may be detected over distances of 500 or even 1000 miles and more. This is normally by a form of tropospheric enhancement, often called "tropo" for short. At times signals may even be trapped in an elevated duct in a form of radio signal propagation known as tropospheric ducting. This can disrupt many radio stations on the FM dial because interference may be encountered that is not normally there.

I was working for WDVE in Pittsburgh many decades ago and as I was driving home when I got to the 70 dBu range of my station I heard my station slowly fade away then this "beautiful Music" station was getting louder and louder it was the WAVE on 102.5 in Tampa Florida and it was tropospheric ducting that made it happen, the best time to catch these "waves" is when its really hot and humid over a large part of the USA.

As a kid, my father would occasionally tune into a station from Boston MA when we were living in Georgia, but it was in the middle of December the last time I saw him do it.

Torqumada

[PMC]

Wave Propagation
When your Father was listening to an AM station, he was receiving the sky wave signal.
The ground wave travels along the ground for often hundreds of miles from the transmitter location. The low frequencies, such as those in the AM broadcast band and lower, produce large ground-wave patterns that produce solid, virtually fade-free reception. This is why he was able to pick up these stations in winter.

Sky Waves
You could also receive sky waves. Sky waves travel toward the sky, rather than hang out on the ground. You would not be able to hear the sky-wave signals, except for the ionosphere. The ionosphere is many miles above the earth, where the air is "thin"--containing few molecules. Here, the ionosphere is bombarded by x-rays, ultraviolet rays, and other forms of high-frequency radiation. The energy from the sun ionizes this layer by stripping electrons from the atoms.
When a sky-wave signal reaches the ionosphere, it will either pass through it or the layer will refract the signal, bending it back to earth. The signal can be heard in that area where the signal reaches the earth, but depending on a number of variables, there might be an area where no signal from that particular transmitter is audible between the ground wave and where the sky wave landed. This area is the skip zone. After the sky-wave signal bounces on the earth, it will return toward the sky again.

Skipping Around the World.
Again, the signal will be refracted by the ionosphere and return to the earth. If the HF signals all bent and bounced off the ionosphere with no loss in signal strength, HF stations around the world would be heard across the earth with perfect signals (something like if a "super ball" was sent bouncing in a frictionless room). Whenever radio signals are refracted by the ionosphere or bounce from the earth, some of the energy is changed into heat, causing absorption of the signal. As a result, the signal at the first skip is stronger than the signal at the second skip, and so on. After several skips, typical HF signals will dissipate.
The skip and ground waves can be remarkably close together. It is not unusual for one station to receive a booming signal while a nearby station cannot hear a trace of the sending station even though using a better receiver with a better antenna. The first station was receiving either the ground wave or the first skip and the other station was located somewhere between these two

[Guest wbottomley]

Paul... in our weather world with doppler radars... we have two things called reflection and refraction. It's amazing how the ionosphere can impact radio waves.

[Guest guest]

Talking Skip, remember that term all too well from my CB heydays. LOL