Service Manual

5-8 Model 340 Telemetry System Revision A
2006920-001
Calibration: Receiver Calibration
Mode Controls
1. Confirm the low-pass filter –3 dB cutoff point of 90 ± 6Hz with an
input of 1.0 Vp-p at TP45 and the output at TP21. Set R61 for a gain
of 2.3.
2. Adjust R177 for a frequency of 8020 ± 20Hz at TP32.
3. Confirm a 10 ± 0.1 Vp-p, 4010 ± 20 Hz square wave at TP33.
4. Confirm the center frequency and the –3 dB points of the switched
capacitor bandpass filters for each IC listed in Table 5-2.
5. With no signal applied, adjust the tone decoders for the correct center
frequency indicated in Table 5-3.
dB
UNITS
AC
VOLTS
DC
VOLTS
888 888 888
Hz Generator
888 888 888
Hz Counter
Table 5-2. Band-Pass Filter Center Frequencies and –3 dB Points
IC Reference Center Frequency –3 dB Point
U17-6 80 Hz 75 Hz, 85 Hz
U18-6 40 Hz 35 Hz, 45 Hz
U23-6 20 Hz 15 Hz, 25 Hz
U27-6 10 Hz 5 Hz, 15 Hz
Table 5-3. Center Frequencies of Tone Decoders
Test Point Center Frequency Adjustment
TP6 10 Hz R95
TP8 20 Hz R99
TP9 40 Hz R110
RP11 80 Hz R149