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From the Q&A

With Russell Kincaid


60 Hz Pickup Circuit

Question:

I have a need for a circuit which will pick up the 60 Hz power line signal as radiated and generate a zero-cross signal.

The circuit is battery powered so it is not connected to the AC mains. The circuit’s main source is a solar-panel array. I would expect an AM-ferrite type antenna and op-amp or FET device could be used.

Paul KJ4UO


Answer:

You don’t say how far from the power line you are. At any rate, the AM radio antenna that is designed for MHz will not be efficient at 60 Hz. While it is true that the US Navy transmits 10 kHz signals long distances, it requires a massive antenna. The 60 Hz transmission lines are designed not to transmit, so any signal will be down in the noise of lightning and automotive ignition. A better solution is to generate an accurate 60 Hz from a crystal as shown below.

The crystal can be pulled a little so if the frequency is off, you can increase C1 and C2 to lower the frequency or decrease them to increase the frequency. The crystal tolerance is typically 50 ppm. I divided the crystal frequency down to 120 Hz then divided by two because the 4060 does not have a Q11 output. The added advantage is that the output is a symmetrical square wave.

The procedure for finding the divider outputs to decode the frequency is this: Divide the input frequency by the output frequency to find the division factor (N). This must be a whole number. Find the highest power of 2 that can be subtracted from N. Do the subtraction; the result being a new value for N. Repeat until the result is zero. The powers of 2 that you use are the Q outputs needed to decode.


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