Patent ID: 6011962
Filing Date: 2000-01-04
Classification: H04B

Abstract:
A circuit for testing the working function of a mobile receiving installation (20) having at least one receiving antenna (5) in a high frequency connection with a superheterodyne receiver (1), the superheterodyne receiver (1) having an image frequency filter (4), an oscillator (9), an IF-signal (11) and a measuring system (10) coupled to the IF-signal for detecting the level of the received signal, the circuit comprising:a circuit arrangement (2) disposed within the receiving installation (20) and coupled to the superheterodyne receiver (1) and the at least one antenna (5), said circuit arrangement comprising:a frequency mixer (3) having a first input coupled to an output of oscillator (9) in superheterodyne receiver (1), a second input and an output, oscillator (9) generating an oscillator signal (8);a feedback loop connecting the IF-signal (11) to said second input of said frequency mixer (3) to provide a self excitation condition, thereby generating an IF-carrier frequency (22), of limited amplitude from the IF-amplifier part of the superheterodyne receiver (1);said frequency mixer (3) producing an HF-output signal (12) having a constant amplitude with respect to time at its output, said HF-output signal (12) having a frequency conforming to a receiving frequency to which the superheterodyne receiver (1) is tuned, said receiving frequency being dependent on said oscillator frequency (8) and said IF-carrier frequency (22);a coupling system (33) having at least one input and coupled to said circuit arrangement to receive said HF-output signal (12), said coupling system coupling said HF-output signal (12) to the at least one receiving antenna (5) or a receiver input,so that the level of the receiving signal of the receiving installation (20) can be determined by said measuring system (10).