Pulsar TCF-10B, System Manual, Page: 121 / 249

On-board voltage regulation is provided by
voltage regulators I8 (+5 V), I12 (+15 V), I13
(-15 V) and associated components. The circuitry
operates at +15 V, +5 V, or -15 V. All bypassing is
to common or PC Board ground. Additional
regulated voltages of +4.3 V and -4.3 V are
generated by I7 to provide an extremely stable
reference for modulating control voltages
(provided by R12, R13, and R14).
11.2.4 Frequency-Shift Operation
(TCF–10B only)
For TCF–10B operation, circuitry is provided to
shift the frequency of the NCO (I4), which
supplies the modulator (I7). Shift-low and shift-
high commands are fed from the Keying Module
to connector pins C/A-24 and C-10, respectively.
The NCO can operate on three different frequen-
cies, depending on the combination of shift-high
and shift-low inputs to the Shift and Control Logic
(I3).
The shift-low command causes I3 to select the
shift frequency voltage from the Frequency Shift
Selector Switch (S5). The NCO (I4) output shifts
to a lower frequency and the Transmitter output
shifts to a lower frequency (f
C
- f
shift
).
The shift-high command causes I3 to select the
shift frequency from the Frequency Shift Selector
(S5). The NCO (I4) output shifts to a higher
frequency and the Transmitter output shifts to a
higher frequency (f
c
+ f
shift
). The operation of this
command is similar to that of the shift-low
command, except that the shift is added to (rather
than subtracted from) the carrier frequency.
When there is no command to shift low or high,
both SL and SH inputs to I3 are logic “1”, and no
shift is added to the carrier frequency.
11.3 TRANSMITTER
TROUBLESHOOTING
Should a fault occur in this module, place the
module on an extender board. Check the RF
output (30 to 535 kHz) on pins A/C-28. If there is
a Voice Key or AM voice input, use an oscillo-
scope to examine the modulation envelope. You
can check the ac and dc voltages provided on the
schematic (Figure 11-2) at the appropriate points,
for the conditions on the schematic (10 W, 1 W,
and Voice).
You can check all diodes, resistors, chokes and
transistors by conventional means.
Page 11–4 April 1997
TCF–10B System Manual
Technologies, Inc.