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Wideband Receiving Loop Array Up and Running

wideband receiving loop array

It’s taken a while, but I finally have my wideband receiving loop array up and running. And, it works great for medium and short wave listening.

More than forty years ago, an article in Ham Radio Magazine sparked my interest in a wideband receiving loop array. In May 1978, Henry Keen W5TRS described an active receiving system useful from 75 through 10 meters capable of directing a null toward the interference source. His system used a couple of short active antennas with close spacing. (See Selective Receiving Antennas on page 20.)

Over the past two years, after I got my first dual channel coherent receiver (Afedri AFE822x) I have been experimenting with diversity reception using multiple antennas to null interference and reduce noise. But what I really wanted to try was building and phasing a wideband receiving loop array.

And, now my dream has become reality.

I have installed two 1-meter loops, each powered by the AAA-1C active antenna amplifier kit from LZ1AQ. What with COVID mail delays, the second amplifier took more than 2 months to arrive. Each antenna is a set of switchable crossed loops, oriented N-S and E-W. Spacing between my loops is 100 feet, or around 30 meters. Each is fed to my shack with equal lengths of CAT7 cable.

You can see my setup in the picture above, thanks Google Maps. A block diagram of the system is shown upper right. Antenna phasing and summing is performed digitally in the receiver.

Wideband Receiving Loop Array Basic Operation

To start out, I have been using this phased array on shortwave using the SDRplay RSPduo, and on medium wave with the AFE822x. Typically, the eastern loop (right, above) supports Tuner 1 on each receiver, and the west loop (left, above) Tuner 2.

Usually, arrays are designed with element spacing between λ/4 and λ/2. At 30 meters spacing, this means the sweet spot for this array is 2.5 to 5.0 MHz. But I find it works well outside this range.

Below λ/4, my pattern has one or two wide lobes, while above λ/2 spacing we find more like 3 or 4 narrower lobes, depending on phasing. On 540 kHz BCB, I can get a 6 dB increase by summing both loops in phase, and a 35 dB null by summing out of phase.

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