Attenuator AT2022 manual

 

 

The AT2022 attenuator module is designed to operate within the intermediate frequency IF section of a satellite transmit or receive chain. The module provides between 2 and 17dB attenuation in 1dB steps selected by 4 control lines (Hex coded). Local and remote operation is possible, remote control is performed via the 15 way D Type connector, local control is selected using the front panel button and control code provided by the Hex switch.

 

A by-pass path provides a fixed attenuation value in the event of power failure. The by-pass mode can be selected locally using the front panel control button.

 

Tellbacks indicate the state of the module, local/remote and control/by-pass (fail) mode is indicated using form c contacts. No path disconnection occurs during attenuation switching and transitions between states are performed smoothly.

A two bar LED indicator provides visual indication for Local and by-pass mode. A DC Power indicator LED (ON) is also provided 

   
 

 Operation

 

The input and output RF connectors are linked within the module by one of two signal paths. The by-pass mode uses the ‘relaxed’ relay contacts and a fixed pi attenuator section. The second path uses the energised relay and the analogue attenuator, this can be set for zero to 15 dB attenuation above the nominal insertion loss. The 4 control lines are decoded to 16 voltage levels that define the attenuation value.

By-pass Mode.

 

This mode is selected using the front panel button. The mode disables the remote and local control lines. The RF relay is de-energised and signals are routed via the fixed attenuator. Tellback contacts indicate when By-pass mode is selected. These contacts are also used to indicate when the module power supply fails.

 

When in by-pass mode the first element of the two bar LED indicator is illuminated.

 

 

Local Operation.

 

Local mode is selected from the front panel, this mode disconnects the remote control lines and selects the value set on the Hex switch. Local operation is reported using class c contacts and by the illumination of the second element of the two bar LED.

 

The switch indicates the attenuation value setting ie. 1 will reduce the signal by 1 dB below the insertion loss, 10 will reduce the signal by 10dB below that value.

 

The attenuation value selected is indicated by the LED bar situated above the Hex switch.

 

 

Remote operation.

 

Remote operation is selected if the module is not in by-pass or local control mode. The module has pull up resistors internally and the default level is the minimum attenuation value. The 4 control lines are routed through the D type and shorting a control line to pin 15 will select that value of attenuation. The control lines should be controlled using clean contacts or open collector devices pulling to 0V (pin 15 on the D Type).

 

The value set remotely is indicated on the four bar LED situated above the Hex switch.

 

An enable pin is made available on the D Type, this pin must be pulled high for the control code to be accepted. If the enable is not ‘high’ the control lines are ignored. If the enable feature is not required pins 1 and 14 should be shorted within the D Type connector.

 

If multiple module control is required the enable pin can be used to route commands to some modules whilst others will not register the changes.

Warnings:

When power is removed from the module the by-pass route is switched into the path. This action causes a break in signal path.

When the module is switched from by-pass mode to local or remote control, if the decoder is not disabled (15 way pin 1 to 14) during switching the attenuator will exhibit a low attenuation value until the control circuitry Restores the required attenuation level (typically 0.5 seconds).

            Specification:

 

52- 88 MHz operation.

16 discrete power settings

Remote/Local control

Smooth power transitions

Compact size

By-pass mode on failure or via local control

Failure alarm

1dB steps.

One set of control connections can operate several modules.

 

 

Connections:

 

Power                              +5V;  0V DC @ 180mA.        15 W D (male)

RF signal                           52-88MHz 75 Ohm.             Max i/p power +20dBm

                                      BNC (female) connector.      VSWR 2:1

                                      Band flatness <1dB

 

Control signals                   Internal connection to +5V via 470 Ohm resistors.

                                      Short circuit to 0V required (four lines).

                                      15 W D (male)

Enable signal                     Pin 14 (+4.5V) - pin 1 (Chip enable).

Alarm/by-pass                   clean contact c/o connections 15  way D (male).

Local control                     clean contact c/o connections 15  way D (male).

Insertion Loss                    <2dB.           

Attenuation steps               0-15dB in 0.5 or 1dB Steps.

 

Please note that specifications can change without prior notice.


          Diagrams.

AT2022 Module Circuit diagram:

Front panel controls:

Power & Control Connections (15W D Type F).

          1        shorted to 14 = control pins enable

2-9            Local Control

2-10         Remote Control

13-5         Normal Operation

13-6         By-pass (fault) state

7                    +4.8 – 5.4V

8                    0V

9                    Control Pins 12(1); 4(2); 3(4); 11(8) – High when o/c

15      0V for control pin earthing (via 470Omh pull ups).