Make sure to encase the oscillator stage in a metallic shield to prevent parasite frequencies destabilizing the oscillating stage.
T2 and T3 works as a buffer stage, T2 as a voltage amplifier and T3 as a current amp. This buffer stage is very important for freq stabilization because is a tampon circuit between the oscillator and the preamp and final amplifier. It is well known that poor transmitter designs tend to modify freq. as you adjust the final stage. With this T2, T3 stage this won’t happen anymore!
T4 is a preamplifier for the fm transmitter and is used as a voltage power rf amplifier and will deliver enough power to the final T5 transistor. As you can see T4 has a capacitor trimmer in its collector, this is used to make a resonance circuit that will force T4 to amplify better and get rid of those unwanted harmonics. L2 and L3 coils must be at 90 degrees angle one to another, this is to avoid frequency and parasite coupling.
The final stage of the long range rf transmitter is equiped with any rf power transistor that has at least 1 watt output power. Use transistors like 2N3866, 2N4427, 2N3553, BLX65, KT920A, 2N3375, BLY81, 2SC1970 or 2SC1971 if you want to have a pro fm transmitter with enough power to cover a long range area. If you use 2N2219 you will get no more than 400mW. Use a good heatsink for the T5 transistor as it gets a little hot. Use a good 12V/1Amp minimum stabilized power supply.
Long range fm transmitter circuit diagram
T1 = T2 = T3 = T4 = BF199
T5 = 2N3866, 2N4427 or 2SC1970 for 1Watt / 2SC1971, BLX65, BLY81, KT920A or 2N3553 for 1.5 to 2W power.
L1 = 5 turns / 0.6mm / 4mm silvered copper
L2 = 6 turns / 0.8mm / 6mm enamelled copper
L3 = 3 turns / 1mm / 7mm silvered copper
L4 = 6 turns / 1mm / 6mm enamelled copper
L5 = 4 turns / 1mm / 7mm silvered copper
Use silvered copper for L3 and L5 if you want to obtain better characteristics.
[h=3]Adjustments of the long range transmitter[/h]Start by construction the oscillator stage, solder a small wire to T1 10pF capacitor out and listening to a fm receiver, trim the 10k pot untill you can “hear
