HP-8504A Vector Voltmeter
Front Panel Features

1. Probe A. Input to channel A. The Voltmeter and Phase meter tune to probe A input frequency.
2. Probe B. Input to channel B. A signal at probe A is required for phase measurement and for channel B amplitude measurement.
3. LINE. Depress to turn on 8405A; lamp lights. Push button retainer unscrews for lamp replacement.
4. AMPLITUDE Meter. Reads amplitude of fundamental component of signal applied to probe A or probe B.
5. AMPLITUDE CHANNEL. Selects channel to be measured on voltmeter.
6. AMPLITUDE RANGE. Sets AMPLITUDE meter scale.
7. PHASE Meter. Reads phase angle between the fundamental components of signals applied to probes.
8. PHASE RANGE. Set phase meter scale. Red ZERO control has at least ±10' range.
9. PHASE FINDER. Overrides PHASE RANGE and PHASE METEROFFSET to select the ±180 phase range and zero offset. Used to find phase angle without changing settings of controls.
10. PHASE METER OFFSET. Used to reduce input phase angle and allow use of expanded PHASE RANGE scales. Not usable unless a definite input angle exists.
11. APC UNLOCKED. Lamp lights to indicate 8405A not tuned. Amplitude is too low and/or FREQ RANGE - MH Z selector is not set to the range which includes fundamental frequency of probe A input.
12. FREQ RANGE - MHz. Coarse tuning control to put input signals within capture range of automatic fine tuning. Selected range must include fundamental frequency of signal applied to probe A.
13. Probe Holder.