Abstract: A portable RF transmitter having an audio plug extending therefrom which mates with the earphone or output jack of an audio source such as a portable battery operated CD or tape player 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 worn by a user. 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 together at audio frequencies by the low impedance of the choke at audio. The choke's leakage inductance also reduces the capacitive reactance of the dipole antenna for better power dissipation. A transformer coupling the RF output to the dipole transforms the impedance of the dipole to a value closer to the output impedance of the RF transmitter.

Abstract: A low noise discriminator circuit having particular utility for use in determining the spectral purity characteristics of an rf signal source and comprising, in addition to standard discriminator components, a down-locked reference signal source including a voltage-controlled signal generator for developing a reference signal and a corresponding train of signal pulses, a stabilizing voltage-controlled oscillator which responds to the discriminator error signal and generates a stabilizing signal having a frequency at least an order of magnitude greater than the frequency of the reference signal, and a sampling phase detector which samples the stabilizing signal at the signal pulse frequency and develops a control signal which is fed through a feed-back loop to stabilize the reference signal generator.

Abstract: A threshold extension device for use in a frequency modulation demodulator circuit to minimize effects of impulse noise, usually referred to as "clicks", which normaly appear in the demodulated output signal, and including a delay line for delaying the demodulated signal, a follow and hold circuit for selectively omitting the click impulses from the delayed signal, a detector for detecting the occurrence of an event which will give rise to a click impulse in the demodulated signal, and a detector driven control signal generator for controlling operation of the follow and hold circuit.

Abstract: An improved squelch circuit for FM demodulators including a low pass filter for filtering out-of-band noise from the demodulator output signals, a delay line for time delaying the filtered signals, a gate for selectively passing the filtered demodulated output signals to an output terminal, and a control circuit for controlling the gate. The control circuit includes a high pass filter for passing the out-of-band noise in the demodulated signals, a detector for detecting the noise level of the noise passed by the high pass filter, and a comparator for comparing the detected out-of-band noise level to a reference to develop a gate control signal which causes the gate to be opened when the out-of-band noise level is relatively low and to be closed when the out-of-band noise level is relatively high.