View Full Version : Antenna help Low Power FM Transmitter

May 7th, 2006, 01:37 PM
I saw in the forums someone was posting question about AM antenna. I am building a low power FM transmitter. The kit comes with a whip antenna which connects by a coaxial line. I am thinking of connecting an amplified FM antenna from Radio Shack to this contraption. Should this boost the signal out just like it boosts the signal into my reciever? I'm a beginner at this stuff so I appreciate any help....




May 7th, 2006, 01:49 PM
Sorry, the answer is no, that amplified antenna is for receivers only. Connecting it to a transmitter will most likely damage the transmitter, amplified antenna, or both.

The best way to get the maximum output of your transmitter is for the antenna to be tuned to the transmitting frequency. If you've ever messed around with CB radio, you've probably heard of SWR (standing wave ratio). Minimizing the swr will tune the antenna for maximum output, also called antenna gain.

What you're wanting is an amplified output stage. Not legal in the US unless you have a broadcast license. I'm not sure, but I think that FM power amps could be pricey.


May 7th, 2006, 05:04 PM
Thanks Kent that's exactly what I needed to know. Didn't want to fry anything in the box in a fool hardy experiment.


May 7th, 2006, 05:58 PM
Just curious, what will be the purpose of your FM transmitter? If it's to be omnidirectional, then precisely tuning your antenna will give you the greatest benefit. If you're transmitting to a specific, fixed point then a directional antenna setup will make your transmitter appear (to the receiver) more powerful than it really is.

Just as an example, we go back to CB radio again :) Have you ever wondered why all the big-rigs have twin antennas? The co-phased antennas radiate power a much greater distance to the front and rear of the truck; however, transmission to the sides is greatly reduced. And as a side note, since the co-phased antennas must be 8 feet apart for CB (27MHz band) this doesn't work for passenger cars and pickup trucks. But it looks cool, don't it? :wink: