Noise Canceller/Antenna Phaser - cheap and easy!
Off and on I've read about noise cancelling and antenna phasing or null-steering circuits and devices. There are plans and schematics for some of them on various web sites and in a few magazines. The magazine articles I've heard about are:
Most seem complicated, expensive or both. But one day I found a circuit in the ARRL Radio Amateur's Library Publication #34, a book called "Radio Frequency Interference" by William Lowry and published in 1978. The schematic diagram is on page 129 along with the parts information and toroid transformer winding details. The parts list calls for FT-82-61 cores but I had a packet of FT-37-61's. I used smaller wire (from an old CRT deflection coil) and added 20% to the number of turns used to compensate for the change in inductance for the smaller cores.
I've only tried it out a little and at first it didn't seem to work. My problem was that the two antennas I used were too different in signal amplitude. After switching from an outdoor longwire and an indoor loop to two pieces of wire indoors, I could get a several S unit null on an AM broadcast band station.
I scanned the page with instructions and schematic to post here.
click image above for full size view, or right-click and save the target image to your disk.
And here's a picture of my breadboarded first assembly attempt.
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