Important: All test points have DC bias on them.
Use the “output” AC terminals and scales on your me-
ter, which places a DC blocking capacitor in series with
the meter.
1. Line Drive Adjustment
Unsquelch the receiver so that continuous noise is
present. Connect the meter to TB1-5 and TB1-6 (line
should also be connected) and adjust R94 (line output
level) for the desired line level (usually 0 dBm or 0.8
V
rms).
2. Transmit Level Adjustment
Disable transmitter PTT circuit. Adjust R92 (line in-
put level) to full clockwise. Have the remote control
console send a continuous PTT command (no voice or
loud room noise). The panel should respond by ener-
gizing the PTT relay and lighting the PTT LED. Adjust
R92 (line input level) for a 1 to 1.1 V
rms reading at
TP11 If the reading is lower, set R92 to maximum. Key
the remote control panel several times to insure reliable
operation of the PTT relay.
Enable the transmitter PTT circuit and monitor its
deviation.
Have the remote control console send a PTT com-
mand plus voice. The PTT relay and the PTT LED
should remain energized. With voice (or a 1-kHz test
tone) coming from the remote control console, adjust
R93 (modulation output level control) for proper devia-
tion.
3. Monitor Adjustments
Momentarily jumper TP2 to TP10 (GND). The moni-
tor relay and monitor LED should light for a timed peri-
od. Adjust R46 (monitor time) for the desired monitor
period. Repeat as required. IF latched monitor opera-
tion is desired, move JP1 to B. If refreshed monitor op-
eration is desired, change JP1 to A, JP2 to B, and JP3
to B.
Have the remote control console send a monitor
command and check for proper operation.
Theory of Operation
Voice Circuits
In the “PTT ON” condition, the voice-signal audio
path is from the line through TB1-5 and TB1-6, T1 and
JP6-A (two-wire), or through TB1-4 and TB1-5, T2 and
JP6-B
(four-wire),
U14A-3,-1,
U11D-8,-9,
R70,
U15A-2,-1, R93, U15B-5, U10B-3,-4, C30, and R79 to
the TX audio output terminal TB1-3. At the PTT tone
frequency (2175 Hz), audio from U11D-9 also passes
through the U14B,C,D bandpass filter and is applied to
U15A-2 180° out of phase, and at equal amplitude to
the signal path through R70. This results in a deep
notch at 2175 Hz and effectively eliminates the PTT
tone signal.
In the receive condition, the receiver audio path is
from TB1-1 through the line-output-level control R94,
U15C-10,8-, U11C-11,10-, R70, U15A-2,1-, U11A-2,1-,
U13, and T1 to the line at TB1-5 and TB1-6. In the
full-duplex mode (JP4 to B), the path is from U15C-8
through U11B-4,3 to U13.
2175-Hz Decoder Circuits
The tone sequence generated at the remote-control
console upon PTT switch operation typically is 2175 Hz
at +10 dBm for 130 ms (guard tone), followed by a
function-tone frequency at 0 dBm for 40 ms, followed
by 2175 Hz at –20 dBm (PTT holding tone) for the du-
ration of PTT-switch operation.
The guard-tone and PTT-tone signal path is from
the line through T1 and JP6-A (two-wire) or T2 and
JP6-B (four-wire), input level control R92, prefilter
stage U5D-12,14-, first bandpass filter U5C,A,B, and
second bandpass filter U4C,B,A to the 2175-Hz de-
tector U1B.
Logic Circuits
CMOS logic is used in these circuits. When the term
“low” is used, the DC voltage is near ground potential.
When the term “high” is used, the voltage is near +9
V
dc.
When the first 2175-Hz tone (guard tone) is de-
tected, TP1 goes low, disabling the receive analog
gates and enabling the transmit analog gates through
U6A-1,2,3 and U7B-2,9. The PTT circuit, however, is
not energized due to the high at U6B-6.
The high-to-low transition at TP1 also triggers the
240-ms timer at U2A-5, causing U2A-6 and U10A-13 to
go high. This enables the audio path from JP6 through
U14A-3,1-, U4D-12,14, and U10A-2,1 to the monitor
decoder U3B,C,D and all other function-tone decoders
which may be connected to P1-3.
In all models except 223C/PCB, RC-223C, and RP-
223C, a frequency-select function tone is always de-
coded during a PTT command toneburst. A low from
this function-tone decode at P1-5 triggers a 50-ms
timer at U8A-5. Upon timeout of the 50-ms timer, a
62-ms timer is triggered at U8B-12. U8B-9 goes low
and, if TP1 has again gone low due to the presence of
PTT tone, the PTT relay K2 is energized from U6B-4
through U9C-3,14. The U8B-9 and the TP1 lows also
hold U8B-14 low through U6C and U12A. This U8B-14
low disables timeout of the 62-ms timer by holding ca-
pacitor C18 in a discharged condition.
When TP1 goes high from the absence of PTT tone
(the console operator has released the PTT switch),
the timing capacitor C18 charges to the timeout voltage
in 62 ms and the PTT relay is deenergized. When the
62-ms timer times out, a new PTT command toneburst
is required to energize the PTT relay; however, if a
PTT tone returns before timeout of the 62-ms timer, the
PTT relay reenergizes. This minimizes PTT losss from
high-level noise transients or from microwave-link flut-
ter. The analog gates are maintained in the transmit
condition during operation of the 50-ms and 62-ms tim-
ers by highs at U7B-1,8 from U8B-10 and U8A-6.
In Models 223C/PCB, RC-223C, and RP-223C no
frequency-select decoders are included, and there is
no decode pulse to trigger the 50-ms timer U8A. The
auto-select-223 P1-8 pin which is shorted to ground by
a 224B frequency-select decoder is high through R54
on models without frequency-select decoders. This
high enables U10D, which causes U2A to time out in
150 ms and allows U9B-15 to go high upon timeout of
the 150-ms timer. This low-to-high transition triggers
the 50-ms timer at U8A-5 through U9G-7,10.
4
223C Series
