1024 TRANSMIT SWEEP GENERATOR

TM 11-5820-918-13

dissipated as heat in a 50-ohm load attached to the 4011 enclosure. A power supply

(3A2A1) in the 4011 routes 115 or 230 VAC power to the 5018 and provides the nec-

essary regulated DC power to run the 4011 assemblies. This power supply is part of

the lower section (3A2) along with the filter decode assembly.

4-13. 1024 TRANSMIT SWEEP GENERATOR - UNIT 1

4-14. The transmit sweep generator (figure FO-1) consists of six principal assemblies:

frequency standard (1A3) ; sweep synthesizer (1A1) ; transmit logic (1A2); numeric

display (1A5); primary power supply (1A7); and battery power supply (1A4). The

transmitter self-test circuits are part of assembly 1A2.

4-15. FREQUENCY STANDARD (figure FO-3) (S/N 400101 and on). The transmitter

timing circuits are based on a 5 MHz standard supplied by a highly stable crystal

oscillator. Contained in the frequency standard module are three assemblies. As-

sembly A1 is the crystal oscillator within a temperature controlled oven; A2 consists

of amplifier and control circuits; and A3 is a switching regulator. The oscillator has

an internal voltage regulator (about 9 volts) which appears at A1J1- 2. This voltage

is used to trim the frequency (coarse and fine) by applying an adjustable DC bias to

A1J1-1. Q1, Q2 and VR1 comprise a voltage regulator to power the unit during normal

operation. If primary power fails, the battery supply on E15 is switched in by CR1.

CR2 prevents the battery voltage from appearing on K1 during a primary power fail-

ure. This allows K1 to close after a few milliseconds delay and bypass CR1 thereby

eliminating the power loss in CR1.

4-16. The switching regulator 1A3A3 (figure FO-4) provides +5 VDC power (+5VB)

for all critical timing circuits of the transmitter. Regulation is controlled by regulator

U1. Switching transistor Q1 and clamping diode CR 1 provide variable width drive

pulses into storage inductor L1. L1-C2 provides the phase shift necessary for oscil-

lation and determines the switching frequency. L2 and C3 form a ripple-reduction fil-

ter. The switching regulator has a 1.5 amp fuse on its input to prevent serious dam-

age in case of a long-term short. Circuit damage from momentary shorts is protected

by internal current limiting (R2).

4-17. SWEEP SYNTHESIZER (P/N 5030-1001 Only) (Refer to figures 4-2, FO-5, and

FO-6). The sweep synthesizer consists of two circuit card assemblies: the micro-

phage synthesizer, operating between 42 and 70 MHz, and the synthesizer converter,

which offsets the microphage output by 40 MHz to produce the 2-30 MH sweep. In

addition, the synthesizer module has two fixed frequency outputs, 5 and 40 MHz,

used in the receiver, and a 2.1-3.5 MHz count output used by the frequency counter

logic. Logic to control the frequency programming of the synthesizer RF sweep is

contained on the converter assembly. This logic digitally increments the synthe-

sizer frequency program every 20 microseconds to produce a linear frequency

sweep. External control inputs to the synthesizer converter logic provide means

to start, stop, reset, and blank the sweep and to select sweep limits and rates.

Transmit blanking of the 2-30 MHz output is implemented by disabling the 40 MHz

mixer conversion of the 42-70 MHz signal. All synthesis operations are based on

an externally supplied 5 MHz standard.