General - HP 8970B Service Manual

Theory of Operation

General

General
The input range of the instrument is 10 MHz to 2047 MHz.
The input signal is first low pass filtered, using the 2050 MHz filter, to avoid images.
The YIG tuned oscillator tunes over the range 3910 MHz to 5947 MHz to mix the
incoming signal to a first IF of 3900 MHz.
The isolator ensures that any rejected signals are absorbed in the isolator and do not
interfere with the front end detector circuitry.
The second convertor mixes 3900 MHz down to 300 MHz. There is a cavity tuned
bandpass filter which is tuned for 3900 MHz. This is set at the factory and should not be
adjusted. The LO input is 600 MHz, but this is multiplied up to 3600 MHz by a X6 circuit.
The 3600 MHz can be monitored at the LO Monitor port.
The 600 MHz supplied to the second convertor comes from a 600 MHz SAW Oscillator.
The frequency is adjusted for 600 MHz 50 KHz. The power should be > -3 dBm.
2-2 HP 8970B Option 020 Service Manual Supplement