I am trying to bode plot a simple audio frequency LC filter circuit. The filter is resonant at a given frequency to terminate a signal a railroad track circuit. The filter is commercially made. I would like to bode plot this to check and see if it is still on frequency and working properly. This would be done on a bench and not out on the track. I have a Velleman PC function generator and a Velleman PC Scope which can function as several interments including a bode plotter. What would be the proper way to connect the filter to this test setup? I have tried connecting it across the function generator and that seemed to overload the generator I also tried connecting it in series with the scope but the filter showed full voltage at all the sweep infrequences. Can someone show a digram of how to sweep test a LC series circuit?


Thanks


Dan

 

OK I post this a few days back.



Here is some more information about the filter circuit I am inquiring about. This is a resonant LC filter circuit that is used to terminate an audio frequency on a railroad track circuit. It does this by acting as an short circuit across the rails at a given frequency. After doing some research on the Internet I would have to guess I need a load resister across the end of the filter. See the schematic. Would this be the proper approach to test this type of filter with a digital scope and a function generator? What should the value of the load resister? Some of the reference texts I have read indicated 1 ohm others 100 ohm.

Dan

 

I would do it like this. Of course, You may need to include the tracks, if they are long. The resistor is your choice, depending on the response you want.
Won't your train's motor short out the audio?

 

What are you trying, to find in train tracks??