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FM Range

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New Member
Can this design be improved to increase the range, im only getting 34m out of it, but i did swap the PN2222 for a BC107, which works up to 100MHz.
The Antenna is a half wavelength piece of hook up wire.
I have no idea how to work out the Power in the Antenna, ive seen one website that worked out the power in the transistor and quoted this as the ERP of the antenna, can it be that simple ?




Active Member
try using it on different receivers. the receiver ur using mite be crap. try somethin like a car radio, they're usually perdy good.

remember that you really cant expect much in the way of range out of these tiny little transmitters.

i think that there must be something wrong w/ ur transmitter tho beacuse i made a 3v transmitter that definetly transmits more than 34 meters. probably like 100 meters w/ my receiver.

bad batteries? :lol:


New Member
Fixed it

Okay i worked on the circuit, laid it out on veroboard, and peaked it. I got a 300m range out of it with a £1.99 reciever, in a built up area. I did detune the reciever to increase the range and the operating stability of the transistors. I also found if you replace the buffer transistor with a 2N3563 you can easily get the same range on Airband.


Well-Known Member
As a side issue, be aware that, due to feedback, the input impedance of the mic amp is on the order of 10k ohms (not 1Meg), so the low-frequency cutoff with the 22nF coupling cap is around 600 Hz. I would change that cap to 100nF.


New Member

Thanks for the info, will experiment,

To detune a receiver you can adjust either the coil or capacitor in the tuning circuit, to get it just below or above the FM band. Usually theres a square box for the capacitor with a screw on each corner, gently adjust each one until you hear the radio start to tune (only one screw will do this) then put the whole thing back together. I got mine down to 85Mhz, its amazing the range you get when you're not competing with alot of signals.
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