100MHz IC based FM Transmitter

New final design. Another LC filter added for better signal purity range. A few inches of wire antenna should cover your living space with good signal strength.

The two 1pf capacitors in parallel can be replaced by a single 2.2pf. The low pas filter has been modified for high input impedance (200ohm) to low output 50ohm impedance of an antenna. I deliberately mistuned it so the final HEX gate delivering 10mW is lightly loaded and it will not overload the previous buffer stages or the LC tuned band pass filters. Sound quality is better than expected! Even music sounds good quality.

Update: The coupling capacitors between N4 and N5  have been lowered to 1p and 1p, from 2p and 6p. In case there is no 100MHz output on pin 8, the two capacitors can be increased to 2p for sufficient drive level to inverter gate N6.

Add 2 x 1pf capacitors in parallel across the 27p
Tuning capacitors in BPF. It gives more leeway when performing the tuning. The two coils have to be stretched a little for 100MHz resonance. BPF and LPF modifications are highly recommend. Here are other possible mods

Del