CLIPPER AND LOW-PASS FILTER (U7A)

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

variable resistor A10A1R2 are connected to give fine

removed and strap E13 to E10 is added. This removes

control for high percentages of modulation and course

keyer driver transistor Q4 from the remote ptt keyer

control for low percentages of modulation. Resistor

circuit and adds a voltage divider composed of resistor

A10A1R6 in parallel with A10A1R7 provides a nearly

R109 (P1-C) or R110 (P1-D) in series with zener diode

constant load to the audio signal from the audio module.

VR7 and resistors R40 and R41. For this strapping

The variable audio output from the modulation control is

option, ptt keyer transistor Q5 turns on whenever the

applied to the clipper and low-pass filter circuits (A4P1-

keying voltage applied to pin C or pin D of P1 exceeds

14/A10J13-14) of audio module A4.

about 4.6 volts.

4-155. CLIPPER AND LOW-PASS FILTER (U7A). To

4-159. Optional 26-Volt Remote Keying. For 26-volt

prevent overmodulation of the transmitter, the clipper

keying, straps E4 to E5. E6 to E7, and E8 to E9 are

(CR3 and CR4 of figure FO-21) removes excessive

removed and strap E13 to E11 is added. This removes

voltage peaks that may be present on the transmit audio

keyer driver transistor Q4 from the remote ptt keyer

signal. The output of the clipper is applied through

circuit and adds a voltage divider composed of resistor

voltage divider R31-R32 to the low-pass filter (U7A). The

R109 or R110 in series with zener diode VR5 and

voltage divider attenuates the audio signal by a factor of

resistors R40 and R41. For this strapping option, ptt

about 0.24 before applying the signal to the low-pass

keyer transistor Q5 turns on whenever the keying voltage

filter.

applied to pin C or pin D of P1 exceeds about 22 volts.

4-156. The low-pass filter (U7A of figure FO-21) shapes

4-160. Optional 48-Volt Remote Keying. For 48-volt

the high-frequency response of the wide bandwidth data

keying, straps E4 to E5, E6 to E7, and E8 to E9 are

to be transmitted. The filter is a 2-pole, active filter with

removed and strap E13 to E 12 is added. This removes

unity gain and cutoff frequency of 25 kHz. The two poles

keyer driver transistor Q4 from the remote ptt keyer

are determined by resistor-capacitor networks R33-C64

driver and adds a voltage divider composed of resistor

and R35-C65. In the passband, the filter response

R109 or R110 in series with zener diode VR6 and

varies less than +1 or -3 dB when referenced to the

resistors R40 and R41. For this strapping option, ptt

output at 1000 Hz. Because of the high cutoff frequency,

keyer transistor Q5 turns on whenever the keying voltage

high-pass filter U7A does not affect the frequency

applied to pin C or pin D of P1 exceeds about 35 volts.

response of the voice audio signal to be transmitted.

4-161. The remote ptt keyer output (P1-A) is connected

4-157. REMOTE PTT KEYER. The remote ptt keyer

to the REMOTE/LOCAL switch (A10A1S3 of figure FO-

(Q4 and Q5 of figure FO-21) converts external keying

16) located on the front panel of chassis A10. When in

information applied to the center tap of the main audio

the remote position, the remote ptt keying signal is

input (P1-C or P1-D) into remote ptt keying (P1-A).

applied to the ptt input (P1-K) of the keyer control circuit.

When operating in the remote mode, the remote ptt

output is applied to the keying control circuit input (P1-K).

4-162. KEYING CONTROL CIRCUIT. The keying con-

Figure FO-16 shows the interconnection between the

trol circuit (Q6, Q7, Q8, Q9, and Q10 of figure FO-21)

remote ptt keyer and the keying control circuit. Strapping

converts ptt keying into two key-line circuits (key 1 and

options on audio module A4 provide for selection of the

key 2) and one ready lamp circuit. Key 1 key line

following types of external keying: normal ground keying

provides fast attack-slow release keying to the 30-MHz

or optional 6-, 26-, or 48-volt keying. Strapping as shown

frequency shift circuit of frequency synthesizer module

on figure FO-21 provides for ground keying. When a

A2, the receiver mute circuit of receiver rf module A3,

ground is applied (keyed) to pin C or D of P1, keyer

and transmit/receive switch in rf filter module A7. Key 2

driver transistor Q4 turns on to forward bias ptt keyer

key line provides slow attack- fast release keying to the

transistor Q5 turning it on. When on, Q5 applies a

transmit/receive switch of frequency synthesizer module

ground to the ptt input (P1-K) of the keying control circuit

A2 and to the ALC circuit of power amplifier module A8.

to key the radio set (remote operation). When the

In addition, when a fault is detected in the phase locked

ground is removed (unkeyed) from pin C or D of P1, +22

loop (p11 fault), or in the rf filter (rf filter fault), or in the

V dc applied through resistors R111, R36, and R37

d/a servo amplifier circuit (rf filter fault), the keying

reverse bias diodes CR1 and CR2. This prevents key-

control circuit inhibits grounding of the key 2 key line and

line noise from turning on keyer driver transistor Q4

turns off the ready lamp.

which is reverse biased by +5 V dc applied through

resistors R38 and R39. When Q4 turns off, ptt keyer

4-163. When the ptt fault (P1-L) and rf filter fault (P1-10)

transistor Q5 turns off to unkey the radio set.

inputs are both logic 1 (no fault), fault switch Q8 is on

and key 2 inhibit transistor Q9 is off. When on, fault

4-158. Optional 6-Volt Remote Keying. For 6-volt

switch Q8 provides a ground to the ready lamp circuit to

keying, straps E4 to E5, E6 to E7, and E8 to E9 are

turn

the

radio

control

4-30