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Simon.T is offline
Oct6-09, 11:35 AM
P: 15
Hi Vk6kro, thanks for the reply again :)

Forgive me if it seems I am witholding crucial information, I did not want to post a huge wall of text in the beginning.

The testing is done with an automated test computer. A signal generator with an output impedance of 50R is connected to a ferrite bead auto-transformer (to transform the output resistance to 200R), this is adjusted down to 132R with a resistor in parrellel (390R off the top of my head).

This output of the auto-transformer is connected to a female connector, which is connected to a male connector on the transmission line. On the other end, the transmission line is terminated into a female connector which is connected to a male connector on the recieving instrumentation.

The instrument we are using for measurements is an AD606 ( which forms part of the automated system. There is a resistor network on its input which presents a 132R input impedance.

All the boards used in this system is through-hole based; having read up on this it seems this is quite terrible for high frequency measurement instruments. All the resistors used are wirewound or metal film type.

Some history: this system has been used for over 15 years and it is only recently I have been involved in investigating this issue. I am certain the equipment is to blame at least in some part (one of the last EEs to look at this system was almost shocked by the design - in a bad way).

Before I waste your time any further, could you recommend a cost effective way to test raw telemetry wire with a seperate setup? We have a wide collection of lab equipment although unfortunately our Signal Analyser is primarily for acoustic measurements (0-102.4 Khz).

Thanks again for your reply :)