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Electronics/impedance matching transformers


Hello. I work in the industry of train control and detection. Within this industry we use a total of 8 frequencies ( from 2970HZ to 3690HZ) modulated onto the tracks to a receiver for train detection. Along with these frequencies, when a train is detected, a frequency of 2050HZ is also modulated onto the tracks representing different speed code rates. All of these modulated frequencies must first go through an impedance matching transformer ( to match the source to an impedance bond) before it is passed to the rail.I have a problem where only the 2050HZ signal seems to be affected intermittently.
  I would like to know, is it possible that the impedance matching transformer is intermittently failing and causing signal reflection which in turn could be affecting my lowest frequency only (2050HZ. Thank you.

Yes, it certainly is possible the transformer is at a malfunction point. If it has worked fine before and is now showing different results then it could be deterioration of the transformer or the level of input signal that may be attenuated due to the frequency band of the transformer.

At the frequencies you are using there is more than likely a bandpass characteristic of the transformer due to leakage inductances and stray capacities; or the transformer may have been designed for a certain bandpass and the lower frequency end of the transformer may be cutting off the 2050 Hz level just enough to give you intermittent or unreliable results.

Impedance matching is often very critical for the transformer when the frequencies are of a particular bandwidth. You might want to check the characteristics of the transformers you are using.  It is easy to measure voltage levels at the frequencies you mentioned using a pretty standard voltmeter.  Knowing the turns ratio of the transformer you should be able to test for the proper ac voltage at the secondary side and get an accurate picture of the transformer performance for each frequency under test.

Hope this helps, but let me know if you need more ideas.  


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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

BSEE University of North Dakota

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