Please provide a schematic for your circuit - it'll be a lot easier to read than transposing from your PCB (which looks good, BTW, at least at first glance...)
Also, please note that this thread is >12 years old. Might be best to start your own thread.
audioguru is still around. Not sure about draco_james
If this discussion is going to develop, one of the moderators could easily split off the new posts into a new thread. (Looks like I could be talking myself into a little job there!)
My comments on the circuit board layout:
1 All the transistors appear to be the wrong way round. ie Collectors to 0v line.
2 The 0v line is isolated from the mass of copper marked ground. It would be better if the ground absorbed the 0v line.
3 interesting use of terminal blocks to represent a coil.
Danlab sent me a "conversation" asking if a line level stereo to mono input modification of my FM transmitter could use a microphone. Since I cannot attach anything in a "conversation" I asked him to make a new thread in the forum.
Here is my FM transmitter with an electret mic and it was made on stripboard. Also here is a pcb of it that I never checked.
I tweaked its parts values to get a very good RF sinewave.
Thank you for answering my questions guys. Starting to build the transmitter.
However, the voltage regulator LM2931 isn't available here. Can i use LM1117 or LM7805 as a substitute? Will it work the same? Thank you very much for your help
The voltage from a 9V alkaline battery is 9V only when it is new and has not been used. Its voltage slowly drops to 4.8V when it is said to be dead.
The LM2931-5 is a low dropout 5V voltage regulator that still regulates when the input from the 9V battery has dropped to about 5.25V.
A 7805 stops regulating when its input has dropped to about 7V which happens soon.
An LM1117 stops regulating when its input has dropped to about 6.1V.
Low dropout regulators need a pretty high value output capacitor for stability as shown on the datasheet.