HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

The M/N voltage-controlled oscillator (VCO) consists of a resonator 

 and 

 with

its associated circuitry. The oscillation frequency is determined by the bias on the varactors

CR1 and CR2 which tunes the cavity resonator. Coarse tuning is provided by Cl, while
C5 is used to vary the output coupling to the cavity thereby varying the output power.
The impedance looking into the emitter of Q2 has a negative real part which provides the
conditions necessary for oscillation to occur.

 is a common-emitter buffer amplifier which provides at least 0 

 output over the 355 to

395 MHz range of the VCO.

 and Q7 form a buffer amplifier to assure that there is approximately 0 

 to drive the

ECL divide-by-2 IC 

 in block 

 R24 and R25 set the proper dc level to drive U2.

Q3 and Q4 provide buffering between the ECL divider 

 and the output.

The VCO tune voltage from the 

 M/N Phase Detector is amplified and applied to the

Voltage-Controlled Oscillator (VCO) by the loop amplifier. The VCO output is amplified,
divided by two, and applied to the 

 Sampler for phase locking the 

 YIG-Tuned

Oscillator (YTO) in 10 MHz increments. A portion of the VCO output provides feedback to
the 

 Phase Detector for phase locking of the M/N Loop.

Spectrum analyzer control settings for 

 troubleshooting:

(KSR)

(SHIFT) 

 (KSF)

                                                                           

3.77

                                                                                   

0 Hz

The tune voltage from the Loop Amplifier can be measured at 

 located on the cover of

the 

 The dc voltage at 

 with the front panel settings indicated above, shoud be

-14.2 V. If an unlocked condition exists, the voltage is approximately -0.5 V or -37.5 V.

If the level is -0.5 V, the probable cause is no VCO output to the 

 Phase Detector.

A level of -37.5 V indicates that the 20 MHz reference to the 

 Phase Detector is not

present.

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