Agilent Technologies HP 8719D Service Manual page 343

This assembly provides stable reference frequencies to the rest of the
instrument by dividing down the output of a 40 MHz VCXO (voltage-controlled
crystal oscillator). One of the divided-down signals is the 100 kHz FN REF
for phase locking the synthesizer signal in A13. Another is the 1 MHz main
phase-locked loop reference signal PL REF that goes to the phase comparator in
All. (The 2nd LO signal and the timing signal for
are explained in "Receiver Theory. ") The EXT REF rear panel input provides
the option of using an external reference with a frequency of 1, 2, 5, or 10
MHz, instead of the internal 40 MHz VCXO.
12.16 Theory of Operation
131.1 - 220/6
142.5 - 234
159.7 - 235.4
178.7 - 223.3
148.9 - 238.2
2550 - 4710
36 4710 - 8256
58 8256 - 13562
85 13562 - 20000
112 20000 - 25000
168 25000 - 40000
the