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Fixed Frequency Group Delay

Question asked by PME75 on Apr 25, 2007
Latest reply on Apr 27, 2007 by PME75
I have an amplifier circuit that splits into three equal outputs.  My specification states that the group delay to each output at xx MHz shall be xx nanoseconds with a tolerance of +/- 5 nS.  The frequency specified is close to 30 MHz.

It looks to me that the simplest method to measure this is to supply the signal to a power splitter with each output into a different value attenuator (so the net output levels are the same) with one output to the input of the circuit and the other to an o'scope reference input. Then take each of the three circuit outputs and connect them to three other o'scope channels using the same length of cable as for the reference.  This way I can measure the Group Delay (time delay) at a single frequency using common test equipment.  This would be done with a single cycle burst of the specified frequency and captured on the o'scope. That way, there is no chance of missing a 360 deg phase shift.

Question:  Is there anything incorrect by doing it this way?

I'm also considering using an E5071C to measure this.  But, it seems like it may take more time to set up and calibrate for this.  Since the frequency is within the range of general purpose TE, and the spec is for a single frequency, and a tolerance not too tight,

is there any advantage to using the network analyzer instead? 

I believe it can not do this at a single frequency, so it would have to select a range about the specified frequency. 

Is this correct?