# Trouble making high pass filter

Discussion in 'General Electronics Discussion' started by Looee, Nov 8, 2016.

1. ### Looee

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Nov 8, 2016
I am trying to make a filter to block out 60 Hz power and pass different frequencies from 1kHz to 5kHz. We first tried a simple high pass filter but our signal and power are going through a transformer. This introduces an inductor into our circuit.
This is similar to the circuit we are trying to build. The problem is that when we actually build the circuit we get a ton of distortion on both the input signal and the output signal. We have used multiple values for the capacitor. I'm assuming we have some kind of resonance which is causing our distortion. The 1.5mH inductor is a fixed value of the transformer so altering that isn't an option. Is there something we are missing? Any suggestions as to what we can do to fix this problem?

Looee

2. ### Harald KappModeratorModerator

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Nov 17, 2011
What do the distortions look like?
The simulation assumes an ideal transformer. Check the real transformer in a circuit without C1, R1. What does the output look like? Is the transformer you're using suitable for that frequency range? Is it suitable for the currents flowng in this circuit (an overloaded transformer may cause heavy distortions due to saturation of the core)?

3. ### Looee

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Nov 8, 2016
Thanks for the suggestion. We used just the xmfr and that did distort the signal. It distorts anything under 30kHz. Is there any kind of 1:1 xmfr that we can use at 1kHz? We are trying to find something fairly cheap but that may not be an option at this point.

4. ### Audioguru

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Sep 24, 2016
Your input signal level is 60V peak! Try it with 1V peak.

5. ### AnalogKid

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Jun 10, 2015
Your question needs a lot of work.

What is it you are trying to do? Separate a multi-kHz signal from the AC powerline? Reduce coupled 60 Hz noise? Why is a transformer necessary? Why is the transformer part number a secret? 60 Hz to 1 kHz is roughly 4 octaves, so a single pole filter will get you 24 dB attenuation of the 60 Hz component and 3 dB attenuation of the 1 kHz component. Is this what you are trying to achieve? At what amplitude/current/power level?

ak

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6. ### Looee

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Nov 8, 2016
We are trying to first couple a 1kHz signal onto the 60 Hz powerline then decouple it on the other end. We are trying to filter the 60 Hz power to keep it from backfeeding our 1kHz signal. We are using the transformer to couple the 2 together. We did find that at 1kHz the transformer distorts the signal. We are using a small transformer with 1mH to 2.06mH inductance. We figured out that by increasing the inductance we can clean up our signal.

7. ### AnalogKid

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Jun 10, 2015
Carrier current signalling has been around for a loooong time, although not at such low frequencies. Look into X-10 home automation components and FM intercoms for time-tested examples of how to transport digital and analog signals on an AC power line. A common aspect of both systems is a much greater difference between the powerline frequency and the information carrier frequency. With the carrier up on the 50-200kHz range, the transformer's resonance does the AC suppression.

ak