User's Manual

RPE 673
TM 1184 Issue 1 AL1 (May 1997)Page A1 - 22
Setting Analogue Deviation
49. To set the Analogue Deviation carry out the following procedure:
a) Select (A)nalogue from the Transmitter Test Menu.
b) Set the audio generator output to 1.25kHz at a level of -13dBm (approximately
11.5mV peak-to-peak as measured on the oscilloscope). Monitor the deviation on
the modulation meter. Adjust RV1 on the Encoder PCB fully clockwise.
c) Refer to Table 6(a) and adjust the generator output level to give a deviation
corresponding to the channel spacing.
d) Increase the signal generator output level by 20dB and adjust RV4 to give a deviation
corresponding to that given in Table 6(b) (this should be the larger of the Peak ‘+’ or
Peak ‘-’ readings on the modulation meter).
Table 6: Analogue Deviation
CHANNEL DEVIATION DEVIATION DEVIATION DEVIATION
SPACING (a) (b) (c) (d)
kHz kHz kHz kHz kHz
25 ± 3 ± 4.5 ± 5 ± 4.9
20 ± 2.4 ± 3.6 ± 4 ± 3.9
12.5 ± 1.5 ± 2.25 ± 2.5 ± 2.4
10 ± 1.2 ± 1.80 ± 2 ± 1.9
e) Reduce the signal generator level by 20dB and re-adjust its output level to give a
deviation corresponding to that given in Table 6(a).
f) Increase the signal generator level by 20dB and re-adjust RV4 to give a deviation
corresponding to that given in Table 6(b).
g) Vary the signal generator frequency between 300Hz and 2.5kHz and check that the
deviation does not exceed that given in Table 6(c). If it does, tune to the frequency
that gives the maximum deviation and adjust RV4 to give a deviation corresponding
to that given in Table 6(d) (this should be the larger of the Peak + or Peak - readings
on the modulation meter).
h) Adjust RV1 on the Encoder PCB as necessary to compensate for the output level
provided by the external audio source at the customers premises.
j) Remove the signal generator.