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Receiving Loop Running Early Tests

receiving loop running

After designing and building, I have the receiving loop running, sort of.

To the left above, you can see the loop tuning board mounted on my loop frame. I 3D printed a couple of plastic holders for the top and bottom of the printed circuit board, which are held in place by wire ties. The wire loops are connected to the screw terminals at the bottom. The terminals on the right of the PCB are used for power, relay switching, and loop tuning voltage (yellow wire).

At the rear, the pickup loop is just connected to some coaxial cable which runs to the NRD-535D receiver (lower inset.) The bench power supply (right) provides the voltage to the varicaps to tune the loop.

For my early tests, I made a list of AM radio stations in Edmonton (3 hours to the north) which I thought might provide weaker signals to pick up during the daytime. One example is CHQT 880 in Edmonton. I then adjusted the voltage supply until the signal peaked.

During this first test I discovered:

  • The large loop did not have enough inductance to reach the lower end of Broadcast Band. It ran out of steam at around 600 kHz.
  • I was hearing some distortion on very strong signals. But most of the signals did not seem as strong as I thought they should be.
  • Sometimes adjusting the capacitance created a noise null rather than a peak.
  • There appeared to be some intermittent connection when I moved the loop.

Back to the drawing board to check these things out, then try again. Perhaps the wire spacing on the loop is too small. Perhaps the impedance mismatch between the pickup loop and 50 ohm receiver input is too much.

Receiving Loop Running on Vintage Power Supply

You might get a kick out of my bench power supply. It is the Heathkit IP-2718. I put this together back in 1976 and it has been a faithful servant. It supplies a fixed 5 volts (1.5A) and two variable 0-20 volts (0.5A each). Only used occasionally, it has spent a lot of time in its box over the years, but is now getting lots of use in my retirement.

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