DATA BUS COUPLERS

Data Bus Coupler is the electronic module where the connection(s) between the Stub(s)/Node(s) and the Data Bus are made. It consists of Bus In, Bus out connections and at least one stub connection. The stub connection is made using a coupling transformer and two fault isolation resistors on the Data Bus end. 

The purpose of the Data Bus Couplers is to prevent a short on a single stub from shorting the main Data Bus i.e. to isolate the main Bus from the terminals, to reduce reflections and maintain signal impedance levels.

Since direct coupled devices (without Couplers) provide no DC isolation or common mode rejection, direct connection to the Bus should be avoided. 

Without Couplers, any short between the device's internal isolation resistors (usually found on the circuit board) and the main Bus will cause failure of the entire Bus. 

In addition to transformers, the Bus couplers have built-in fault isolation resistors providing protection for the main Bus in event of a short circuit in the Stub.

There are two basic styles of Data Bus Couplers using either connectors or cables attached. The Couplers with cables attached are known as In-line Data bus Couplers and with connectors directly attached to the Coupler box/case are known as Connectorized Data Bus Couplers. 

Bus Couplers are available in various configurations from single stub to multi stub. The In-line type is used in applications where lightweight and small size is important. 

All the devices such as the Bus controller, Bus monitor and remote terminal must be connected to the stub ends of the Coupler only. Data Bus will provide a single data path between the Bus Controller and all the associated remote terminals.

Both ends of the Bus, whether it includes one Coupler or a series of Couplers connected together, must be terminated with 78ohms terminators on both ends of the Bus.

Some Couplers have built in terminators and are generally used at the ends of the Bus in multi Coupler applications for on board use, but limit the flexibility of test lab set-ups.

Features:

• 1Watt Isolation resistors 
• 1Watt Terminating resistors
• -55°C to +125°C operating temperature.

Benefits:

• Qualified and type approved for flight applications
• Low cost
• Highly reliable
• Fast delivery

Electrical specifications:

• Coupler Module : Encapsulated with the following components
      *Coupler Transformer to MIL-T-21038
      *Fault protection Resistors to MIL-R-39007
• Transformer Turns ratio : 1:1.41 ± 3% (Compliant to MIL-T-21038 Std)
• Input Impedance : 3000W Minimum (75KHz to 1MHz)
• Droop : 20% maximum (250KHz)
• Overshoot and ringing : ±1peak (250KHz square wave with
• 100ns maximum rise and fall time)
• Common mode rejection : >45dB at 1.0MHz
• Fault protection : Resistor in series with each Bus winding
• connection equal to 59±1% W, 1W
• Termination : 78 ± 2% W, 1W
• Operating Temperature : -55°C to +125°C
• Storage Temperature : -55°C to +130°C
• Stub Voltage : 1.0V to 14.0V p-p, line-line