6043 POWER DIVIDER UNIT 3

TM 11-5820-917-13

voltage for the IF amplifier. The voltage also goes to an AGC output amplifier,

U20, which is used to drive the AGC bargraph on the 6025 display.

4-82. The receiver is generally sweep-tuned through the HF band. Occasionally,

the receiver sweeps through a strong signal which may cause the narrow-band

filters to ring for a long period of time, thereby desensitizing the receiver

immediately afterwards. To reduce this effect, a blanker circuit is used to detect

the presence of an approaching large signal and to momentarily turn off the input

to the IF amplifiers, Transistors Q24-32 (figure FO-33/5) form a separate IF ampli-

fier with a bandwidth wider than that of the main IF amplifier, such that, as the

receiver is sweeping, it will detect a large signal approaching the main IF band-

width before it appears in the main IF passband. When such a signal is detected,

a one-shot, U22, is triggered which, for approximately 10 milliseconds: (1) dis-

connects the IF input to the crystal filter in U1 and terminates the filter input by

U2, and (2) holds the prior AGC level by opening Q22 in the AGC detector. The

blanking sensitivity control is normally set to blank the IF amplifier if the approach-

ing signal is 25 dB or greater above the currently received signal or noise.

4-83. RECEIVER POWER SUPPLY (figure FO-34). The receiver power supply

provides all the DC voltages used in both the 6025 and 4028 units. Regulated volt-

ages supplied to the 4028 unit are +-5V, +12V, and -24 VDC. The remaining

unregulated supplies are routed to the 6025 unit and are regulated there. (See

paragraph 4-63.) In the 4028 unit, the +12V, -12V, and +24 VDC outputs supply

both the synthesizer and receiver modules while the +5V outputs supply only the

synthesizer. The duplication of some DC supplies is provided to assure separation

of noise signals between unrelated inputs. An internally mounted toggle switch

(S2) is provided for selecting 115 or 230 VAC inputs. In addition, some compen-

sation for small increments of input voltage variations may be made by altering

terminal board (TB1) connection adjacent to the transformer. (Refer to para-

graph 5-14 for adjustment of these connections.)

4-84. 6043 POWER DIVIDER UNIT 3

4-85. The receiver uses three separate fourway power dividers to interface with

receiving antennas. AU connections should be of 50 ohms impedance. The power

divider results in an output on each port approximately 6 dB below the input. Each

divider provides minimum isolation of 30 dB over the entire 2-30 range.

4-86. FREQUENCY STANDARD SECTION (S/N 400100 and before)

4-87. FREQUENCY STANDARD (1A6) (figures FO-35 and FO-36) (S/N 400100

and before). The receiver timing circuits are based on a 5 MHz standard derived

from a 10 MHz temperature-controlled quartz crystal oscillator. Both the oscilla-

tor-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 Q02 regu-

lated 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.