Fm transmitter works in PCB but not in Protoboard

Do you mean the kind where you push wires into holes in plastic, with no solder?

If so there is probably to much capacitance in the protoboard iself. Protoboards like that are best for digital signals at maybe 20 MHz or less. They are not good for radio circuits in the 100 MHz range. At radio frequencies the geometry of the circuit can matter just as much as the connections. Look at the inductor - all it is is a long piece of wire, but at radio frequency it doesn't behave like a wire at all. To radio frequency parts of the circuit that you call connections are actually little inductors and capacitors - inductors and capacitors that aren't supposed to be part of your circuit.

Yes I mean the kind where you push wires into holes in plastic, with no solder.

Strangely the fm transmitter works well in PCB but not in the protoboard.

It is not strange at all if you read my message... what would be strange is if it did work on the proto board - anyone will tell you that's a bad way to build it.

A good way to build prototype RF circuits is to get a piece of plain undrilled, unetched copper coated PC board. Glue the transistors and ICs to it upside down and solder the passives between the leads, up in the air. Anything that goes to ground gets one lead soldered down to the copper foil and the other sticking up in the air to support the circuit. If you need extra support, use the largest value resistors in your junkbox as standoffs.

I'd agree they're not particularly "good" in the 100MHz range, although I have a book where the guy builds all sorts of oscillators up to ~100MHz on solderless breadboards -- his goal being to let people easily play with the circuits.

Personally I'm amazed at how difficult it often is to obtain, e.g., 60dB of isolation between anything on a circuit board by the time you get to a couple GHz... That's "only" 1mV being induced from 1V, which "seems" like it should be easy to obtain... but no....

Thanks for your answers cs_post and Joel.