AIR TRAFFIC COMMUNICATION FACILITIES

VHF COMMUNICATIONRS SERIES 200TRANSMITTER SU 251RECEIVER EU 231

SINGLE CHANNEL RECEIVER

EU 231 Front Panel

DESIGNRx Unit EU 231 is plugged into Power Supply IN 201A or IN 201D, thus establishing the connection to the peripherals.

CONFIGURATION

RECEIVER MODULES

BLOCK DIAGRAM

EU 231 BLOCK DIAGRAM

RF SectionIn the first control stage, the antenna signal is attenuated by the PIN diodes (depending on the signal strength) and routed to the first bandpass filter. The signal then passes through the second control stage and is amplified. Having passed through the second bandpass filter, the signal is converted in the mixer stage into the first Intermediate frequency of 10.7 MHz

Synthesizer

A microprocessor programs, controls and monitors the synthesizer via a serial bus. The synthesizer consists of a prescaler, the actual synthesizer IC, a VCO and a phase>locked loop (PLL). The reference frequency is obtained from a temperature>compensated 10>MHzcrystal oscillator (TCXO). With Mod. 23, an oven>controlled crystal oscillator is used as the reference source. By means of coding switches the frequency is set. The locked state of the PLL>VCO is indicated by a green LED.

IF SectionThe 10.7>MHz IF signal from the mixer passes through several amplifier stages and two crystal filters. The second mixer converts the signal to the intermediate frequency of 1.3 MHz, and this signal is fed via the following filter to the amplifier stage and the demodulator. In addition, an AGC control voltage is generated. From the first IF, a logarithmic amplifier generates a signal which can be employed for evaluating the receiver.

AF SectionThe AF signal is preamplified and noise can be suppressed by the noise blanker. Subsequently the AF signal is fed to the AF AGC control circuit and the filter board. Via various AF switches the output is regulated. The volume of the loudspeaker is adjusted with a volume control. The S/N evaluation circuit generates the squelch criterion.

AF Switchover Section (MAIN / STBY)

In the automatic switchover mode with two correlated receivers the AF switchover circuit determines that the receiver with the better signal quality becomes main receiver, whereas the other receiver operates as standby unit.

Sum Test CBIT (Continuous Built in Test)Via the sum test the entire receiver is continuously monitored (continuous built in test). The signals from the oscillators, the synthesizer, the IF stages and the remote control are combined to form the sum signal. The operating voltages are monitored in just the same way. A test connector simplifies fault detection.

Remote ControlThe serial signals of the REM BUS are stored and converted into parallel signals. The logic circuit combines the control signals for the receiver. In the other direction, status signals of the receiver are converted into serial data telegrams via the REM BUS. At the connectors CONTROL and AF the control and status signals are available and permit remote control via parallel lines.The optional inband interface converts data telegrams via control tones (in the AF voice channel) into parallel control signals. In the other direction, status signals of the receiver are converted into control tones.

Power SupplyThe input voltage of nominally 24 VDC is converted by a DC/DC converter with regulator

POWER SUPPLY BLOCK DIAGRAM

Switch Over Concept

Strart Up and Test

Start Up and TestIf LED VOP (8) is illuminated, the DC / DC converter in the Rx unit is working and the 12 VDC supplied are within the nominal range.If LED TEST (4) is illuminated, the receiver is functioning properly, i.e. all required operating voltages are available, the oscillators and the synthesizer function properly.As long as the receive signal is above the by means of the SQ control, LED SQ (10) will remain illuminated.In the case that one of the indicator LEDs is not illuminated according to the table, perform troubleshooting in line with chapter 4.2, as necessary.

Required Test Equipment for TroubleshootingAn accurate check of the receiver's technical data requires a complete radio communications tester. We recommend the R&S Radio Communication Tester CMTA 54.If no such radio communications tester is available, the following alternative test equipment may be used:

For checking the frequency error and frequency spacing: Frequency counter: frequency range up to 150 MHz, accuracy of at least 10 Hz

For checking the receiver sensitivity: RF generator: 100 to 150 MHz, AM and FM AF voltmeter: with integrated AF filter

For checking the voltage, current and impedance: Digital multimeter: conventional

Troubleshooting with the Aid of Indications

Contd

TRANSMITTER SU 251

Front View

Rear View

TRANSMITTER BLOCK DIAGRAM

Design

Block Diagram

Modulator Block Diagram

Sinthesyzer Block Diagram

Amplifier Block Diagram

Regulator Block Diagram

Power Supply IN 251 Block Diagram

Display Board Block Diagram

Interface GI 201 Block Diagram

Main Standby Connection

Function of Controls and Indicators

Contd

Contd

Troubleshooting Table

Contd

Contd

Contd

Contd

Frequency Setting

TRANSCEIVER

Control Panel GB 409

Rear View

Block Diagram