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How to convert FM broadcast watts to distances?

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emission

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Hello

Most of FM broadcast device come with watts units

My question is how to convert this to distance ?

Example :

If I have 5W FM transmitter what will be the area or distances covered by this transmitter ?
Thank you
 
You'll find that the answer to this varies with terrain, obstacles such as buildings, mountains, forests,etc.. The old rule of thumb I was taught ,was 1 mile per watt on average, your milage may vary.. Another determining factor is operating frequency...
 
lets say i want to cover 700km sq area (belive it or not my country total surface .... its small island)

with normal houses and building not more than 3 floor to 10 of buildings and we have no mountains or forests !

and all of these houses and buildings are on 1/4 of the total surface .
 
It also depends a lot on the sensitivity of the radios.A good FM tuner is much more sensitive than a cheap crappy radio.
 
You also need to think about the antenna design. You could use an omnidirectional antenna which spreads the power out (mostly) equally in a circular shape around the antenna, or a directional antenna which sends more radiation in some directions more than others. That way you can get more distance from the same power, but only in one direction. (Actually it can be more than one direction but the idea is the same.)

So if you're near the centre of the island you might want an omni antenna, say, but if you're near one end of the island (what island? what country?) then you might use a different antenna design so you can direct the signal over the land and not send half of it out over the water.

Audioguru or RadioRon will probably be along to correct me if I'm leading you too far astray--they understand this better than I do. :)


Torben
 
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i am on this island and i am in the capital and its as you see in the top of the island

https://maps.google.com/maps?hl=en&ie=UTF8&ll=26.066652,50.531616&spn=1.63325,3.433228&t=h&z=9



Torben said:
You also need to think about the antenna design. You could use an omnidirectional antenna which spreads the power out (mostly) equally in a circular shape around the antenna, or a directional antenna which sends more radiation in some directions more than others. That way you can get more distance from the same power, but only in one direction. (Actually it can be more than one direction but the idea is the same.)

So if you're near the centre of the island you might want an omni antenna, say, but if you're near one end of the island (what island? what country?) then you might use a different antenna design so you can direct the signal over the land and not send half of it out over the water.

Audioguru or RadioRon will probably be along to correct me if I'm leading you too far astray--they understand this better than I do. :)


Torben
 
The FM band is somewhat “line of sight”. The waves will not go through mountains or around corners. The antenna height will be very important.

I had a 10 watt transmitter with a antenna height of 70 feet on a small hill. The antenna had a gain of 2x and there was some loss in the transmission line so my effective radiated power was about 18 watts. The station reached about 15 miles over flat land. When I climbed the tower I could see 15 miles. There was a neighboring town that had a number of people with “TV” antennas 20 feet in the air. They could receive the signal. From a 70 foot antenna to a 20 foot antenna 25 miles was possible.

There is no good formula. Antenna grounding is a factor. Type of soil. How much water. Small hills will cause a shadow. As I think back before the 10 watt transmitter we had a 5 watt transmitter with a 0.8x antenna and 50 feet of height. We struggled to get 5 miles.

For commercial applications a week signal will not do. If people want to tune you in they will put up with a week signal.

Go to http://www.ramseyelectronics.com/ They have a 50 watt radio station kit.
 
I am somewhat certain that this issue is addressed in amateur radio handbooks and other publications. As already mentioned, the entire system needs to be included in the analysis - the results are approximations but provides a good place to start.
 
As people have already said. There are too many variables and factors to consider before giving a good answer.
I always say where every you can see from the aerial you can get (aslong as the rig has the power)
5watts of power at the aerial id safely say 3 miles with well matched aerial/good swr.
What aerial are you using?

Let me know if you want any help or parts/amps/circuits
 
Hello emission,

for a rough check use a model globe. Place a ruler perpendicular on the transmitter's position and measure the vertical distance between the ruler and the surface at the most distant point of the island. Convert the measured distance into height und you'll have an almost perfect solution for your transmitter's mast height.

For the transmitting power you must experiment a bit since you can't take all local influences into consideration.

Bosco

P.S. I guess you'll come up with a 300ft high mast.
 
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The most practical way for you is to listen to the VoiceFM (200W in Manama) station, and go around the country to see how well they perform. Be sure to test with both a good receiver and a crappy one. Learn what you can from their antenna tower and site.

The rest of the FM stations in your country are from 1kW to 100kW, probably for good reason.

Probably a good idea to check the regulations, too, before buying a transmitter. Many Arab countries don't allow privately owned broadcasters.
 
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