HP 8901B

Adjustments Model 8901B
VERTICAL
INPUT
-
A23TPl
‘SAW AWL’
OSCILLOSCOPE
Adjustment 4
0 0
SIGNAL SOURCE
INPUT
:::;: 000000 O 0000 0
,” BBBB 0 OUTPUT
0 0 0 000000 0 0000 0
SAMPLER EFFICIENCY AND OFFSET
Service Sheet 18
Description
Using the track-tune mode, the two signals into the sampler are configured so that the low-frequency
VCXO
is at a set frequency and the high-frequency VCO tracks the RF input signal. The output of the
sampler is observed on an oscilloscope. The
FtF input is tuned to locate a zero-beat frequency at the
sampler output then tuned for a
1 MHz beat. The sampler offset and efficiency (or frequency response)
are then adjusted
so that the dc offset is 50 mV and the amplitude of the 1 MHz waveform is the same
as the zero beat.
NOTE
Improper adjustment of efficiency may result in the loop easily breaking or
not attaining phase lock.
Equipment
Oscilloscope ...................................................................... HP 1740A
Signal Source..
...................................................... HP 8640B or HP 3336C
Figure 5-2. Sampler Efficiency and Offset Adjustment Test Setup
Procedure
1. Set the signal source to 18 MHz CW at 0 am.
2. Connect the equipment as shown in Figure 5-2. (The oscilloscope input should be ac coupled.
The signal source can be connected either to
a sensor module or directly the the Modulation
Analyzer’s INPUT.)
3. Set the oscilloscope’s vertical sensitivity to 0.2 Vldivision and horizontal scale for 10 ps/division.
4. On the Modulation Analyzer, press the blue key then press INSTR PRESET (the AUTOMATIC
OPERATION key) to preset the instrument. Press TRACK MODE.
If the instrument fails to
tune to the 18 MHz signal, key in 18 MHz then press TRACK MODE.
5-8 Adjustment 4