Racal Instruments RA-117 User Manual page 38

for an output of 200 V approximately for 100 A on front panel meter. Check that
the bandwidths agree (approximately) with the folowing figures:-
-6dB
3.0 kc/s
100 c/s
300 c/s
1.0 kc/s
7.0 kc/s
13.0 kc/s
Crystal Filter
18. Remove the 1 7 Mc/s crystal XL300 and set the controls as in 14. above. Set the
BANDWIDTH switch to 300 c/s. Connect the signal generator to socket SKT303.
Tune the signal generator slowly through the passband and observe the crystal re-
sponses ( and
1
the signal generator to the mean of
mum output. Reset the signal generator frequency to 100 kc/s and adjust the output
to produce a reading of 100 A. Set the generator frequency to 101,025 c/s, increase
the output by 66dB and adjust the phasing control C199 to obtain minimum out-
put (i.e. the point of recection occurs). Increase the generator frequency slowly and
ascertain that the meter reading does not exceed 100 A. Slowly decrease the signal
frequency until 100 A reading is obtained and check that the frequency is not greater
than 100,900 c/s. Tune through the passband, adjusting the signal generator output
as necessary to avoid meter damage. Note the highest frequency at which a signal
generator output equal to that used at 101,025 c/s gives an output an output of a
100 A. This frequency should not be less than 99,100 c/s.
19. Slowly decrease the signal frequency and ensure that the output does not rise above
100 A. Decrease the generator output by 66dB and re- check the frequency response
within the passband, re-adjusting C110 and C148 if necessary. Set the signal generator
frequency to 100 kc/s and adjust the output for 100 A level. Increase the signal
generator output by 6dB and check the bandwidth for 100 A output. The bandwidth
should be between 270 and 330 c/s and the mid-position should not deviate from 100
kc/s by more than 25 c/s. The sensitivity should be approximately 200 V for 100 A
deflection.
20. Switch the BANDWIDTH control to 100 c/s. Repeat the procedure with signal gener-
ator frequency settings of 100,925 c/s, 100,800 c/s and 99,200 c/s. Adjust the phasing
capacitor C118 only. The 6dB bandwidth should be between 80 and 120 c/s and the
deviation from the mean less than 25 c/s. For 100 A output, the input should be
approximately 150 A.
21. Disconnect the signal generator and refit the 1 7 Mc/s crystal.
Use of Digital Frequency Meter
22. The alignment of the I.F. amplifier and in particular the crystal filter involves the
measurement of frequencies to far greater accuracies than those normally obtainable
Alignment Procedures
-66dB
15 kc/s
Less than 1.5 kc/s
Less than 2.0 kc/s
8 kc/s
22 kc/s
35 kc/s
). Care must be taken as the tuning of these is very sharp. Retune
2
1
Sensitivity for 100 A
Less than 200 V (Measured in-
put becomes reference level)
)
) To be within 10dB of
) reference level
) measured on 3
) position
and and adjust C110 and C148 for maxi-
2
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