SMALL RF TRANSMITTER WITH NO EXTERNAL ANTENNA

摘要

A portable RF transmitter (16) having an audio plug (18) which mates with the earphone or output jack of an audio source (10) and having no external antenna. The portable RF transmitter modulates audio signals from the audio source onto an FM carrier and transmits them to an FM receiver mounted on a headset. The RF transmitter uses its own ground circuit and the ground circuit of the audio source as two elements of a short dipole. The two ground circuits are electrically isolated at RF by an RF choke but connected at audio frequencies by the low impedance of the choke at audio. The choke's leakage inductance also reduces the capacitive resistance of the dipole antenna for better power dissipation.