Unit 2, 4028 HF RECEIVER

TM 11-5820-917-13

Provide a digital display of the actual frequency being received; and,

i. Provide self-test circuits and display to determine a go/no-go condition of

the receiver power supplies, receiver sensitivity, proper synthesizer operation, and

standby power supply voltage.

1-7. Unit 2, 4028 HF RECEIVER. The 4028 consists of a frequency synthesizer, an

HF radio receiver, and power supply. The frequency synthesizer generates a pre-

cision frequency spectrally pure output signal, 40.2 MHz above the desired received

frequency which is used for the HF receiver first mixer LO injection. The synthesizer

frequency is programmed by digital control circuits and is phase-locked to an oven-

enclosed 5 MHz crystal oscillator in the 6025 unit.

1-8. The receiver assembly mixes the sweeping first local oscillator signal from the

frequency synthesizer with the input as selected from one of three antenna sources.

The result is a 40.2 MHz first intermediate frequency (IF) which is crystal-filtered

to provide a 10-kHz bandwidth. A 40-MHz second local oscillator and mixer converts

the first IF to a 200-kHz second IF which is further bandwidth-limited to approximate-

ly 500 Hz by a second crystal filter. The receiver's AGC circuit seeks to maintain a

constant amplitude second IF output which is then mixed with a 200-kHz third LO

signal to provide a 0-500 Hz baseband audio output.

1-9. The receiver has a calibrator circuit for testing receiver sensitivity y. When the

test function is initiated, this circuit injects a low level sweeping RF signal into the

receiver input that produces a 350 Hz tone in the receiver output. The presence of

this tone in the spectrum analyzer output verifies proper receiver operation. The

front end of the receiver also supplies up to 30 dB antenna input attenuation, operator

selected in 10 dB steps. Half-octave preselection filters in the receiver front end

reduce the potential interference effects of high level out-of-band signals. A

speaker and headphone jack are also provided enabling the operator to listen to the

receiver's audio output.

1-10. The power supply for the RCS-4B receiver is contained within the 4028. This

supply is a linear, series regulated solid state supply providing +5, +12, -12, and

+24 VDC .

1-11. Unit 3, 6043 POWER DIVIDER. The power divider consists of three 4-way

power dividers that can be connected to each of three broadband antennas. One out-

put of each power divider goes to the corresponding antenna input of the 4028

receiver. The other three outputs of the power dividers are available for antenna

connection to communication receivers. Because of the antenna sharing technique,

the ionospheric sounding obtained by the RCS-4B accounts for receive characteristics

of the antenna used by the communication receivers.

1-12. EQUIPMENT SUPPLIED

1-13. As supplied, the RCS-4B receiver includes the following standard items:

P/N 6025-1000

Control/Display, Unit 1

P/N 4028-1000 or 4028-1100

HF Receiver, Unit 2

Power Divider, Unit 3

P/N 6043-1000

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