More number of dipole in one FM tower, why?

[Willen]

All the FM stations has more dipole antenna as an output. For why? Are thy use more RF amplifier of same friquency for more power? And according to number of amplifier, are they use more dipole?

 

[davenn]

more dipoles increases the overall antenna gain. they are usually done in what is called a phased array.

a bunch of antennas gives good gain and is much much cheaper than an equilivent amplifier of the same gain!!

as a fellow ham radio friend of mine likes to say "gotta love aluminium amplifiers"

also to improving the gain of the system cheaply, when using a bunch of antennas like that it is easy to adjust the radiation patten of the antenna system so that it can be directed to cover certain areas more efficiently

cheers
Dave

 

[audioguru]

Two yagi antennas stacked one above the other cut the signal that goes very high and into the ground and concentrate the signal parallel to the ground to go far.

Two yagi antennas stacked side by side cut signals from the sides and concentrate the signal in one direction to go far.

 

[Willen]

more dipoles increases the overall antenna gain. they are usually done in what is called a phased array.

a bunch of antennas gives good gain and is much much cheaper than an equilivent amplifier of the same gain!!

as a fellow ham radio friend of mine likes to say "gotta love aluminium amplifiers"

also to improving the gain of the system cheaply, when using a bunch of antennas like that it is easy to adjust the radiation patten of the antenna system so that it can be directed to cover certain areas more efficiently

cheers
Dave

Wow! Then, at the same rf output connection, can I add one or more dipole in my 1.5 watt FM Tx without modifying circuit? (for high gain and great range) Does it increase directionlity or works as omnidirectional?

 

[audioguru]

The gain of a phased array antenna is increased because it is more directional and it concentrates its power in a single direction (it is not omni-directional).
If you want omni then some of your signal goes straight up into space and some goes into the ground under your antenna.
A dipole is directional in 2 directions and has poor response in 2 other directions.

 

[davenn]

Wow! Then, at the same rf output connection, can I add one or more dipole in my 1.5 watt FM Tx without modifying circuit? (for high gain and great range) Does it increase directionlity or works as omnidirectional?

if you are using dipoles vertically polarised then that phased array will have an omni directional radiation pattern
this system is also used for VHF/UHF mobile radio repeater stations.
It will only be directional if the dipoles are horizontally polarised

Dave

 

[Willen]

Dave forgot to write ''cheers'' in last of his sentence ha ha

> If so, I think- it is not bad to connect more dipole at single rf output connection to get great performance!!!!!
For two parallel dipole, should i've to connect using differnt coax from Tx or using same single coax and connect parralel dipole at top?

 

[RCinFLA]

The dipoles' impedance will change due to their proximity to each other. They also have to be phased properly. For a broadside vertical array this is usually same phase feed. The matching must be correct to get full yield of directivity from array. For the vertical FM station the directivity is a narrower omni directional azimuth beam toward the horizon.

UHF television antennas from tall towers often phase the array to have a slight downtilt from the horizion. Their beam may point at ground about 15 to 25 miles from the tower. They can also create a cardioid pattern by the radiator proximity to the the mast to reduce radiation in a given direction and accentuate it in other direction.