4011 POWER SUPPLY

TM 11-5820-918-13

4-51. 4011 POWER SUPPLY (figures FO-27 and FO-29). The power supply, along with

components of the filter decode assembly, provides the 4011 unit with +5, +6, +26, -240,

and -270 volts DC . In addition, the power supply provides power line switching for

the 5018. Power to the 5018 unit is routed via a contactor (K1), having normally open

contacts. The contactor coil is operated from the 4011 26 VDC line so the 4011 must

be on before the 5018 can be turned on. This arrangement ensures that the 5018 will

not delivery RF power to an inactive filter set.

4-52. As with all units in the transmitter, the 4011 has its own 230/115-volt selector

switch. This is located after the line filter and power switch, and prior to the primary

of T1. Some variations of input voltage can be compensated for by using different

taps on T1. On the secondary side of T1, the -240 VEC bias voltage for the filter de-

code is developed by adding -270 volts and +30 VDC. The +5 and +6 VDC regulated

voltages (figure FO-27/1),supply the TTL digital decode logic and the filter drivers

respectively. Power to the 1024 is not switched by the 4011 unit; however, both units

do use a common power input plug.

NOTE

The later serial numbered units (S/N 400101 and on) develop the 240

VDC bias voltage using -270 and +30 volts as described. In earlier units

(S/N 400100 and before), a bias voltage of -250 VDC is developed using

-270 and +20 volts. Other than these value differences, the circuit is

the same for all units.

4-53. FREQUENCY STANDARD (figure FO-30) (S/N 400100 and before). The trans-

mitter timing circuits are based on a 5 MHz standard derived from a 10 MHz tempera-

ture controlled quartz crystal oscillator. Both the oscillator-amplifier and the oven

controller portions of the oscillator require a stable 10 VDC input. This is provided

by regulator U3 from the battery or Q102 regulated primary power source. An LC

circuit comprising L1 and C10 further isolates the oscillator portion from switching

transients. On the return side of the oven circuit, Q101 provides current limiting

to safeguard against current surges during the initial oven heater warm-up period

(approximately 5 minutes). The 10 MHz output of the oscillator is divided by flip-

flop U2 down to 5 MHz (internal standard) and fanned out to buffer gates U1 for use

by the timing circuits as independent 5 MHz, 50 ohm sources.

4-54. SWITCHING REGULATOR (figure FO-31) (S/N 400100 and before). This circuit

regulates the +5-volt power input to the primary timing circuits of the receiver. The

circuit is basically intended for regulation of the battery supply during a power failure.

However, in normal operation, a line power derived source of 29 VDC (from CR4+,

figure FO-32) is routed through the same circuit allowing unbroken interruption of

power should a supply failure occur. The high efficiency (65%) circuit contained on

this board uses a low current drain voltage regulator connected as an oscillator (U1)

in which an inductor (L2) is used in the feedback loop as an energy storage device.

By cent rolling oscillation, the inductor effects internal conduction of the regulator/

oscillator, thereby controlling voltage. A 1.6A current limiter (Q4, Q5, and Q6) and

a 6 volt, 5 watt, overvoltage protector (CR6 and CR10) are included as an integral

part of the circuit. A related circuit senses the input line to determine if the battery

voltage is less than 16.3 volts. This is achieved at U2 by comparing the received

voltage to two zener diodes, the difference voltage thereby controlling Q7, which in

turn controls turn-on of oscillator U1.

4-17