DESCRIPTION. 1-2. The Hewlett-Packard Models 618C/620B SHF Signal Generators (Figure 1-1) provide RF signal output in the frequency ranges of 3800 to 7600 MHz, and 7000 to 11,000 MHz respectively. At least 1-mW power output is available over the entire frequency range. The output frequency is indicated on a direct-reading dial. The RF output power is adjustable by an attenuator that is calibrated in µV and dB. 1-3. Five types of modulation are available: internal pulse modulation, external pulse modulation, internal frequency modulation, external frequency modulation, and internal square-wave modulation. 1-4. The internal pulse modulation has a variable repetition rate of 40 to 4, 000 Hz. Pulse width is variable from 0. 5 to 10 us as measured at the pulse 50% amplitude points. Internal square wave modulation is variable from 40 to 4,000 Hz. 1-5. The Signal Generator can be modulated by external pulses of positive or negative polarity. The amplitude of the modulating pulses may be 20 to 70V, and the pulse width between 0.5 and 2500 µs. 1-6. Internal frequency modulation comprises a sawtooth sweep rate of 40 to 4,000 Hz. Frequency deviation is variable from 0 to 5 MHz over most of the band. External frequency modulation from an external sine wave is provided. Frequency deviation is approximately 5 MHz. 1-7. Synchronization outputs of the Signal Generator comprise two types: delayed, and undelayed. The delayed synchronization output is a positive pulse that occurs simultaneous with the RF pulse. The pulse has an amplitude of 25 V minimum and a rise time less than 1 µs when terminated in a load of 1000 ohms or more. The undelayed synchronization pulse has the same characteristics as the delayed pulse, except the pulse occurs between 3 to 300 µs (as adjusted by front-panel control) before the RF pulse. 1-8. Both the pulse- and frequency-modulated RF output may be synchronized with the following externally generated signals: sine waves of 40 to 4, 000 Hz, and 5 to 50V amplitude; pulses of 40 to 4,000 Hz, a peak amplitude of 5 to 50V, a rise time of 0.1 to 1 µs, and a width of 0.5 to 5 µs.