Low powered FM transmitter

[ljones]

Hello all (new here!),

I understand this is off-site (and hopefully not in the wrong place in the forums) but a few years back I decided to construct a simple FM radio transmitter. Long distance didn't really matter to me then, so I decided to choose the most basic design I could possibly find, which I found here;

http://www.uoguelph.ca/~antoon/circ/fmt2.htm

However, for the life of me I could never get this to work; the coil I made seemed to do nothing, the sound was distorted and the whole thing seemed to "transmit" even when the 3V power was removed (leaving only the audio input!).

I understand that there are FM transmitters with PCB designs here, though PCB design and construction is *well* beyond my abilities x.x .

Does anyone know of anything simpler - or prehaps even maybe a low-powered AM transmitter would be easier?

Thanks,

ljones

[audioguru]

Hi,
The antenna length for an FM transmitter is reasonable because it operates at the very high frequency of about 100MHz. AM radios operate at a frequency 100 times lower so a transmitting antenna should be 100 times longer.

A very high frequency transmitter needs to be made with very short wires because long wires are inductors and side-by-side wires have capacitance at very high frequencies.
Somebody made an FM transmitter on perf board but with long wires and it didn't work. I made mine on perf board (actually it is stripboard) with very short wires and it works perfectly. Here iare pics with the comparison: