directional antenna for fm broadcast

[xrayzebra]

I'm thinking of using an FM25 for an "unofficial college station" at a small art school. I want broadcasts to mainly reach people in a building across the street from a building I own, across a broad boulevard, maybe half a block away with no obstructions... perfect line of sight for the department where the signal is intended to be received, so students can share broadcasts of their favorite tunes. I'd let everybody have a chance to make mp3 playlists that would be broadcast from a computer on a daily schedule.

My building is in a densely populated area, and I don't want to risk bothering people on the other side of my building. I'd like to just beam the signal at the school building with a little gain, and have the signal not very strong in the other direction.

Beyond the building I am trying to "hit," there is a freeway and a railroad yard, so I don't think that I will cause any trouble in that direction.

Anybody got a simple, cheap solution? I'm real new at this, so don't be afraid of "talking to me like I'm stupid." I'll take no offense at very elementary instruction. [img]smile.gif[/img]

The building has a mostly glass front, and only one or two solid frame walls to penetrate. I think the FM25 has enough juice if I get some directional gain. If not, I can probably place it inside the building I am trying to serve. I was only thinking of putting the gear in another building so nobody knows where to go to steal it! [img]smile.gif[/img]

Thanks.

[finley]

Why don't you try the FM25B with the built-in antenna and see? Your signal should carry just fine across one boulevard, and it shouldn't "bother" anyone in your building at that power. Locate your transmitter by a window that faces the target building.

If it's not quite enough signal, there are MANY good suggestions for external antennas in earlier posts on this forum. But, you may not need one at all. Try it.

[Antonio]

You can use a simple dipole antenna installed in a metal post, separated by a distance equivalent to 1/4 of wavelenght of your transmitting frequency. To determine the lenght of 1/4 of wave just use this simple formula: x=(11811/f) x 0.25 where x=lenght in inches and f=frequency in MHz. Example: for 100MHz x=(11811/100) x 0.25 =29.53 inches. That's the total lenght between your dipole to your post. This will give you a front gain of 3db (3db = double of the power) with some power decrease in the back of the metal post...

[ March 23, 2004, 06:41 AM: Message edited by: Tony2004 ]

[ac5dk]

Get a standard receiving twinlead type "folded dipole" and a balun at any radio shack... hang it in a window facing the building. It will provide a better match than the built in whip, and the window frame will make it bi-directional... the building behind it will sort of change that to ONE direction.

Good Luck!!!

Kevin