Exciter Assembly A1A2

TM 11-5825-271-34

nects the external battery to the unregulated supply line

is reduced to zero when the TONE switch S3 is switched

through isolation diode CR10.

off. When the voltage at the cathodes of CR28 is zero

e. AC Remote Monitor. A secondary winding of T1l

(S3 off), the oscillator ceases to produce an output

Transistor Q9 Is an emitter follower, providing a low

on the transformer chassis provides 20 Vac across P1-1

impedance tone output to the keyer gate Q10

and P1-2 (fig. FO-3). The output between P1-1 and P1-

f. Keyer Gate. Field-effect transistor Q10 provides

3 can be used for monitoring at a remote site. This

transient-free gating of the 1020 Hz tone signal from Q9

output can be adjusted by R4 from 0.5 to 5.0 Vac, when

When the keyer control signal at the gate of Q10 is high,

terminated by a 600 ohm load.

Q10 is off and the tone is not fed to Q11. When the

keyer control signal is low, Q10 is switched on and the

2-15. Exciter Assembly A1A2

tone signal is connected to amplifier Q11. The keyed

(fig FO-5 (1))

tone signal from Q11, routed through R67 and C30, is

a. 12Vregulator. The +24 Vdc at P1-14 is scaled

used as the modulation signal for the mark/space

down to +12V by R13/R14. Transistor Q1 is a voltage

modulator

follower, providing a low Impedance + 12V supply for

g. Voice Compressor. The external voice input at

circuitry within the exciter assembly A1A2.

P1-17 is applied to the base of Q22 through R72 and

b. RF Oscillator. The switched 24 Vdc for the rf

C35 Field-effect transistor Q20 acts as a variable

oscillator is received at P1-5 from contacts 4-7 of

resistor, controlled by the feedback from Q37 of the low

shutdown relay K1 (fig. FO-1). When 24 Vdc supply at

pass filter. If the signal at output of the low pass filter,

P1-5 is present (normal operation), the rf oscillator circuit

exceeds the dc bias at the base of Q21 (set by

operates at 10 times the carrier frequency. Crystal Y1,

COMPRESSION LEVEL potentiometer R13), Q23

operated at series resonance, introduces positive

conducts and reduces the bias at the gate of Q20 This

feedback from the collector of Q3 to the base of Q2.

reduces the drain-source resistance of Q20 and

The signal level at the emitter of Q3, approximately 12V

therefore the signal level applied to Q22 At the same

p-p, is applied to the frequency divider U9 Note that in

time, Q23 switches on Q19 which lights the

the event of a malfunction, shutdown relay K1

COMPRESSION LIMIT lamp connected to P1-16 Diode

deenergizes, and the 24 Vdc at P1-5 is switched off.

CR34 and resistor R77 provide a fast attack/slow decay

Thus, the rf oscillator ceases to operate and the NDB

characteristic to the compressor circuit

transmitter is effectively turned off.

h. Voice Amplifier. Transistor Q22 provides high

c. Frequency Divider. Integrated circuit U9 divides

gain amplification of the voice signal The output from

the rf output from the oscillator circuit by 10 to produce

Q22 is buffered by emitter follower Q24 and applied to

the transmitter carrier frequency. The output at U9-12,

the high pass filter circuit

12V p-p, is buffered by Q4. Transistors Q5 and Q6 form

i. Voice Filter. The voice filter consists of a high

a complementary output stage which produces a square

pass filter formed by Q25 through Q30 and a low pass

wave output at the carrier frequency.

filter comprising Q31 through Q37 Together they form a

d. RF Filter and Detector The square wave carrier

six-pole, Chebyshev filter which is flat to within 3 dB from

signal from Q5/Q6 is passed through a low-pass filter to

300 to 3000 Hz, falling off sharply below and above these

remove unwanted harmonics. The filter covers the

frequencies. The output from the voice filter is buffered

frequency band of 320 to 535 kHz when links 3 and 4 are

by Q37 and fed to the mark/space modulator through

removed, or a frequency band of 190 to 320 kHz when

R113 and C52.

links 3 and 4 are in place. Transformer T1 converts the

j. Sawtooth Oscillator. Transistors Q12, Q13, and

output impedance of the filter to 50 ohms for proper

Q14 form a sawtooth oscillator operating at a frequency

matching with the pa module A1A4. Diode CR24 and

of approximately 65 kHz The output at the emitter of Q14

capacitor C14 form a peak detector and its output at P1-

is a linear ramp, rising from 3 4V to 10 4V.

7 is routed to TEST switch S2 and TEST meter M1 (fig.

k. Mark/Space Modulator. Transistors Q15 and

FO-2) to provide an indication of the drive level.

Q16 form an emitter-coupled slicer circuit The sawtooth

e. Tone Oscillator. Transistors Q7, Q8; and Q9

signal from Q14 is applied, through L4, to the base of

and associated components form a phase-shift oscillator

Q15. The potential at the base of Q16 is proportional to

operating at 1020 Hz The symmetrical clipping of the

the instantaneous audio level and the preset carrier level.

feedback signal by CR27 and CR28, and the variable dc

When the base of Q16 is at a constant potential, a 1 4V

bias at the cathode of CR28, allows adjustment of the

square wave signal with a constant pulse width is

output level (tone modulation depth) from the tone

developed at the collector of Q15 However, if the

oscillator.

The dc bias at the cathode of CR28,

potential at the base of Q16 rises, the conduction period

developed by R115 and ONE LEVEL potentiometer R12,

2-6