Amplitude-Modulated Calibration Generator

A calibration generator is used for quickly checking receiver operation. The design shown here generates RF signals (markers) at 1 MHz intervals over a frequency extending up to about 2 GHz. These signals can be amplitude- modulated by driving T4 with a sine wave generator. A stable 2 MHz oscillator is set up around Xi and Ti. MOSFET T2 functions as a digital buffer for clocking bistable/divider FFi. Pulses at the out- put of FF2 have a frequency of 1 MHz and a width of only 12 ns, which is ob- tained by FF2 clearing itself after output Q has gone low. The pulses drive T3 into saturation. This SHF transistor consequently produces a wide spec- trum of harmonics, and its class C set- ting causes it to function as a frequency multiplier. The collector current can be modulated via series transistor T4. Since the two sidebands generated in the pro- cess of amplitude modulation are offset from the carrier by the modulation fre- quency, AM can be used to generate signals at frequencies i...