Did anybody notice that most of the FM transmitters have the same problems:
1) The antenna is connected directly to the tuned LC of the oscillator so anything that moves toward or away from the antenna changes its capacitance and changes the capacitance of the tuned circuit so the frequency changes all over the place.
2) Most circuits do not have a voltage regulator so the frequency also changes as the battery voltage runs down.
3) Most circuits do not have pre-emphasis (treble frequencies boost) so the de-emphasis in every FM radio will play them with a muffled sound like your stereo with its treble tone control turned all the way down.
4) Most circuits are mono, not stereo. The BA1404 IC is stereo but it is obsolete and its RF frequency drifts all over the place.
The BH1417 circuit is modern, has a quartz crystal controlled frequency synthesizer for a rock solid RF frequency, has pre-emphasis and is stereo with fairly low distortion. Throw away 99 of those old poor performance circuits.