AN/PRC-128

Overview

The Scope Shield Radio System consists of the following;

• Adapter Group OF-185/PRC (VA)
• Radio frequency power amplifier (PA)
• AN/PRC-128 handheld radio (PRC).

The items repairable at depot level are the power supply/audio (PS/A) assembly of the VA, the complete PA (including alternate module) and the RT portion of the PRC/128 (including alternate module).

The AN/PRC-128 radio system (PRC) consists of the following

• A receiver/transmitter (RT),
• Low band long range (LBLR) antenna;
• Low band short range/high band (LBSR/HB) antenna;
• Low band (30 to 88 MHz) and high band (130 to 174 MHz) RF/IF modules (one installed, other is alternate);
• Carrying pouch;
• Lanyard
• Two rechargeable nickel-cadmium (NICAD) batteries.

The PRC is a two-band handheld receiver-transmitter. The PRC provides short range, ground-to-ground voice communications in the low VHF-FM (30 to 88 MHz) and high VHF-FM (130 to 174 MHz) bands.

10-channel Operator Programmable-frequencv Capability

The RT stores up to ten programmed channels (12.5 kHz increments) anywhere in the operating frequency range. A programmed RT can program another radio with channel/frequency information via a frequency transfer cable.

Antenna Matching Switch

The thumbwheel switch selects the proper antenna matching network for the transmit frequency. The "50" position provides a direct 50

ohm interface for test use. The "50" position is used for 130 to 174 MHz operation or with any 50 ohm external antenna. An antenna warning tone is activated if the switch position is incorrect with respect to the operating frequency.

Warning Tones.

The RT generates two separate warning tones; a low battery tone and an antenna mismatch tone.

Liquid Crystal Display.

A five-digit display indicates frequency, operational mode, and programming information to the operator.

Half-duplex operation.

The PRC can transmit and receive utilizing a separate frequency for each channel programmed in the half-duplex mode.

Technical Specifications

RT GENERAL CHARACTERISTICS

Frequency ranges

30.0000 to 87.9875 MHz and 130.0000 to 173.9875 MHz

Minimum channel spacing

25 kHz (+/- 25 kHz spacing to operate; can program in 12.5 kHz increments)

Available channels

4640 (30-88 MHz band), 3520 (130-174 MHz band)

Preset channels

10 (stored in non-volatile memory)

Operating modes

Clear Voice (Simplex and Half Duplex) FM

Operating voltage

11 to 16 Vdc, 400 mAdc maximum.

Low battery warning tone

Four 400 Hz beeps at six second intervals when battery voltage drops below preset level

Antenna mismatch tone

1000 Hz tone at 2 second intervals if selected operating frequency and ANT match switch position do not agree

RT RECEIVER CHARACTERISTICS

Sensitivity

0.5 microvolts for 12 dB SINAD*

Selectivity (+/- 25 kHz)

-50 dB for 30-88 MHz, -60 dB for 130-174 MHz

Squelch sensitivity

0.5 microvolts (maximum), noise operated

Spurious response

-60 dB

IF rejection

-60 dB

Audio output

Power

100 mW (nominal) into 47 ohms

Distortion (@ 100 mW)

10% (maximum)

Frequency response

300 to 3000 Hz (+1, -6 dB)

Hum and noise

Unsquelched

30dB below rated audio out

Squelched

50 dB below rated audio out

• SINAD = Signal + Noise + Distortion Noise + Distortion

RT TRANSMITTER CHARACTERISTICS

Power output

1.0 watt (minimum into 50 ohms)

Spurious harmonic attenuation

43 dB below carrier (min.)

Frequency stability

5 ppm (maximum) of operating frequency

Audio

Frequency response

300 to 3000 Hz (+1, -4 dB)

Harmonic distortion

10% (maximum)

Modulation

+/-3 kHz, limited at 5 kHz (130-174 MHz)

+/-4.5 kHz limited at 7.5 kHz (30-88 Mhz)

FM hum and noise

30 dB below nominal deviation level (Low Band only)

Squelch tone

150 +/- 2Hz'

PA CHARACTERISTICS

Frequency ranges

30.0000 to 87.9875 MHz and 130.0000 to 173.9875 MHz

Input power

25 - 28 Vdc, 3.0 Adc maximum

RF Power Output (50 ohm load)

BYPASS mode;

1 watt (ref. rf input)

AMPL mode;

10 watts minimum, 20 watts maximum (internal adjust)

Spurious harmonic attenuation

60 dB below carrier (minimum)

Reference rf input level

0.25 watts minimum from RT

RCV mode signal loss

1.0 dB max

PS/A CHARACTERISTICS

Input power

10 to 32 Vdc; 150 watts max.

Output power

14.5 to 15.5 Vdc @ .5 Adc max (RT).

26.0 to 27.0 Vdc @ 3.0 Adc max (PA).

Charger current

Nominal

30 mA

Short-circuit

90 mA

RCV Audio Output

Power

2.0 watts nominal into 8 ohms

Distortion @ 2.0 Watts

10.0 % maximum

Programming Frequencies

Simplex

1. Set the CHAN switch to the channel number to be reprogrammed
2. Turn the radio off for a few seconds then back on
3. Press SET within 10 seconds of turning the radio on, the Radio will be in programming mode, if one digit is shown in the display
4. Press the INCR button until the LCD shows the desired digit
5. Press the SET button. The next digit is displayed
6. Repeat the above SET & INCR sequence until the complete frequency is displayed on the LCD
7. Press the SET button to store the channel, LOAd will be displayed indicating that the channel frequency assignment has been stored.
8. Change the CHAN button within 10 seconds to program a new frequency

Channel Steps
The last two digits can only be 00, 12, 25, 38, 50, 62, 75 or 88, due to the channel step of 12.5 kHz

Duplex

The Radio can use a split transmit and receive frequencies, usually used in repeater operation. The process is the same as with simplex except for a single step

Program the Receive Frequency

1. Set the CHAN switch to the channel number to be reprogrammed
2. Turn the radio off for a few seconds then back on
3. Press SET within 10 seconds of turning the radio on, the Radio will be in programming mode, if one digit is shown in the display
4. Press the INCR button until the LCD shows the desired digit
5. Press the SET button. The next digit is displayed
6. Repeat the above SET & INCR sequence until the complete frequency is displayed on the LCD
7. Press and hold the PTT button, then press the SET button to store the channel, LOAd will be displayed indicating that the channel frequency assignment has been stored. The Transmit frequency is ready for programming.

Images

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Reference Files

TO 31R2-4-810-3

MAINTENANCE INSTRUCTIONS WITH ILLUSTRATED PARTS BREAKDOWN

RADIO SET

AN/PRC-128 (PN 901608-801)

RP [sic] POWER AMPLIFIER (PN901603-801)

ADAPTER GROUP

OF-185/PRC (901602-801)

18 November 1999