Measuring Retun Loss

Jan 22, 2007 1 Replies

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Hi All,

I would like to do some return loss calculations using LTSpice Spice, using the Wheatstone Bridge Method.

Eg this Wheatstone circuit here

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Return Loss in terms of source an load impedances is defined here

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However , return loss can be measured using the Wheatstone Bridge method and measuring voltages accross the bridge to compute the Return Loss. (may be similar to this circuit

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This is for POTs Telecom Impedance circuits 0 ~ 4kHz where the reference impedance may be complex or 600R

QUESTION Can any one suggest a simple Wheatstone circuit where I can measure voltages to compute the return loss - source against load impedance.

Thanks in advance

Joe

Yes, lets assume a 50 Ohm system

You feed your circuit under test from a swept voltage source through a

50 ohm series resistor that creates the proper source Z for the generator. Set the Voltage source to 2 Volts. Call the junction of the 50 Ohm resistor and your circuit node 2.

Now when your circuit exhibits the correct load Z of 50 Ohms, there will be 1 volt at the junction node 2.

Now you connect a divider consisting of 2 equal resistors (any value will work in simulation ) also to the voltage sounce. And the junction of the two divider resistors you call node 99. This node is also 1 volt. So now you just have to measure the voltage DIFFERENCE between node A and B and express it in dB and this is your return loss.

i.e.

Trace Add DB(V(99)-V(2)) OK

this will work for any Z system, just change the first series resistor to the correct value...

Mark

Measuring Retun Loss

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