Table 4-2. VCO and Radio Control Frequency Versus VCO Band

TO 31R2-2GRC171-2

TM 11-5820-815-14

NAVELEX 0967-LP-544-5010

midband, or high-band vco generates the synthesizer

4-67. The following details operation of individual

output signal which appears at the transmit rf output or

functions of the synthesizer. Unless otherwise speci-

receive injection output. The band decoder processes

fied, reference designators apply to components of

10- and 100-MHz frequency select informa- tion from the

frequency synthesizer module A2.

radio control and transmitter key line (key 1) information

to enable one of the three voltage- controlled oscillators

4-68. BAND DECODERS.

The synthesizer uses

in accordance with table 4-2. The power splitter couples

NAND and NOR gate logic to decode transmitter key line

the vco signal to the synthesizer output and to the

information and 10-, 20-, 40-, 80-, and 100-MHz radio

variable divider input and provides isolation between the

control frequency select information into frequency band

two paths. Rf amplifiers amplify the vco signal to the

information. The low-band decoder (figures FO-19 and

proper level for receiver injection and transmitter

4-2) provides a logic 1 output voltage through resistor

excitation. Key 2 controls the transmit/receive switch to

A2A7R18 to enable the low-band vco, A2A1, whenever

select either the receive injection output during receive

the radio control is set below 250 MHz in transmit mode

mode or the transmit rf output during transmit mode.

or below 280 MHz in receive mode. The high-band

The regenerative divider, 2-modulus prescaler,

decoder (figures FO-19 and 4-3) provides a logic 1

programmable counter, and Np programmable counter

output voltage through resistor A2A7R20 to enable the

form the variable divider which divides (as described

high-band vco, A2A3, whenever the radio control is set to

previously) the output of the power splitter by N to give

320 MHz or above in transmit mode or to 350 MHz or

12.5 kHz at the frequency/phase detector when phase

above in receive mode. The midband decoder (NOR

locked. The reference divider divides the output of the

gate A2A7U21B of figure FO-19) decodes the outputs of

3.2-MHz frequency reference by 256 to provide a 12.5-

the low- and high-band decoders to provide a logic 1

kHz reference signal at the reference input of the

voltage through resistor A2A7R19 to enable the midband

frequency/phase detector.

The frequency/ phase

vco, A2A2. The mid- band decoder output is only logic 1

detector compares the two signals and generates an

when the low- and high-band decoder outputs are logic

asymmetrical output waveform whose duty cycle is

0. This occurs when the radio control frequency is set

proportional to the phase difference between the two

between 250 and 319.975 MHz for transmit mode and

signals. The low-pass filter filters the waveform into a dc

between 280 and 349.975 MHz for receive mode. Truth

tuning voltage that is proportional to the duty cycle. The

tables for the low-band decoder and high-band decoder

tuning voltage drives the vco to the proper frequency. In

are given in figures 4-2 and 4-3 respectively.

the variable divider, 30-MHz decode and transmit/receive

control logic decreases the division ratio by 30 whenever

4-69. VOLTAGE-CONTROLLED OSCILLATORS.

the transmitter is un-keyed to decrease the synthesizer

The low-band, midband, and high-band voltage-

output frequency (receive injection output) by 30 MHz.

controlled oscillators, A2A1, A2A2. and A2A3 (figure

The lock monitor compares the frequency reference to

FO-19 and figure 4-4) are identical except for the

the variable divider output to provide a pll fault logic

inductance value of L1 and capacitance value of C4.

signal when- ever the synthesizer is not phase locked.

These components allow the oscillators to be adjusted to

cover the three different frequency ranges of the

Table 4-2. VCO and Radio Control Frequency Versus VCO Band

RRADIO CONTROL

VCO FREQUENCY

FREQUENCY

(MHz)

ENABLED

(MHz)

VCO

XMT MODE

RCV MODE

XMT MODE

RCV MODE

LOW-BAND

225.000 thru

195.000 thru

249.975

279.975

249.975

MIDBAND

250.000 thru

280.000 thru

250.000 thru

319.975

349.975

319.975

349.975

HIGH-BAND

320.000 thru

350.000 thru

320.000 thru

399.975

369.975

4-13