Electrical Frequency Synthesizer 1A14/2A14 Functional Operation

TM 11-5820-695-35

This circuit tunes out the varactor capacity at the 150

2-12.

Electrical Frequency Synthesizer 1A14/2A14

MHz frequency. Variable capacitor C1 is accessible

Functional Operation

from the front panel and is used when aligning the tuned

a. General.

circuit. The tuned circuit also prevents rf from leaking

(1) Two

identical

electrical

frequency

back to radio transmitter modulator 1A8. The 4.55 to

synthesizers are used in Radio Set AN/GRC-144. One

4.85 GHz local oscillator fundamental frequency is

is in Transmitter, Radio T-1054/GRC-144 and is

suppressed in the tuned varactor cavity by two tuned

designated I A14. The other is in Receiver, Radio R-

stubs C4 and CS5, producing sidebands containing

1467/GRC-144 and is designated 2A14. The transmitter

frequency modulated 150 MHz signal. The sidebands

and receiver local oscillator operating frequencies are

are reflected out of the tuned varactor cavity, enter the

derived from the associated electrical frequency

circulator at port number 2, and leave at port number 3.

synthesizer.

The electrical frequency synthesizer

The 4.4 to 5.0 GHz (approximately 315 milliwatts)

generates one output signal selectable within the

output from port number 3 is applied to radio frequency

frequency range of 284.375 MHz to 303.125 MHz which

bandpass filter 1FL3 which is tuned to the desired

is subsequently converted (external to the electrical

sideband and passes the selected sideband to radio

frequency synthesizer) to an operating frequency within

frequency low pass filter 1FL4. The unwanted sideband

the range of 4400.0 MHz through and including 5000.0

is reflected by 1FL3 to port number 3 and applied to port

MHz.

number 4 of the circulator where it is absorbed in a

(2) The electrical frequency synthesizer

dummy load. The circulator also provides a detected

output frequency is selected by setting thumbwheel

sample of the 4.65 to 4.85 signal (3rd multiplier) to the

switches. This frequency is increased by frequency

meter selector switch on meter panel assembly 1A16A8.

multipliers and mixers in the T-1054/ GRC-144 (or R-

Variable resistor 1A15ASR2 on the back of meter panel

1467/GRC-144) to the required final operating

assembly 1A115A8 is used to calibrate the 3RD MULT

frequency. Thumbwheel switch settings on the electrical

meter indication.

frequency synthesizer are direct reading and are

(2) Radio frequency bandpass filter 1FLS has

calibrated to indicate (in MHz) the operating frequency

a maximum 3 db bandpass of 38 MHz and is tuned to

of the T1054/GRC-144 (or R-1467/GRC-144), not the

the desired frequency in the 4.4-.0 GHz band by setting

electrical frequency synthesizer output frequency.

the filter's tuning knob to the appropriate frequency.

(3) The electrical frequency synthesizer is an

The bandpass filter passes the desired frequency

application of the phase-locked loop principle. The

through radio frequency low pass filter 1FL4 and

electrical frequency synthesizer uses a voltage

directional coupler 1DC1 to the antenna system. The rf

controlled oscillator (vco) to generate the output signal.

power output from directional coupler lDC1 to the

The accuracy of the frequency of the vco is maintained

antenna system is 2,50 milliwatts (nominal).

The

by a crystal oscillator standard (operating at 8 MHz).

directional coupler provides three additional outputs

The output signal of the vco is returned, through a

(monitor ports). Two of the outputs are dc levels which

feedback network which lowers the frequency, and it is

indicate the transmitter's forward rf power and reflected

compared in phase with the crystal oscillator standard

power.

These outputs are applied through alarm

frequency. A difference in frequency between the vco

monitor 1A5 to the meter selector switch on meter panel

signal and the crystal oscillator standard frequency is

assembly 1A15A8.

Potentiometers 1A15A8R5 and

detected as a phase error.

A phase error detector

1A15A8R6 on the back of lA15A8 are used to calibrate

generates a signal which in turn adjusts the frequency of

the REFL RF POWER and RF POWER meter

the vco as required. This feedback loop is designated a

indications, respectively. The third output from the

phase locked loop since it locks the vco frequency in

directional coupler provides a sample of the 4.45.0 GHz

step with the crystal oscillator control frequency.

output signal which is 21 db down from the mainline rf

(4) The subparagraphs that follow describe

power output signal. This sampled signal is applied to

the correlation between the thumbwheel switch settings

crystal mixer 1A16Z1 of the radio test set.

and the electrical frequency synthesizer's rf output

frequencies, the correlation between the transmit

operating frequency and the electrical frequency

synthesizer rf output frequency, the correlation between

the receive operating frequency and the electrical

frequency

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