I’ve got an ever increasing noise floor at my QTH so I thought I would try an active HF loop to see if I can null out the worst of the noise.

I found a simple design on-line and used it as the basis of my loop. The original site unfortunately no longer exists but I did manage to save the design here.

Loop-schematic

I followed the design but I placed 2 sockets on the board for the transistors as I wanted to try different combinations. I don’t have many pictures of the build but I used a waterproof box, a section of 15mm PE-X pipe with a thick wire running through it for the loop and filled the completed box with epoxy to hold everything in place.

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The loop is 1M in diameter. The amplifier is powered via the coax using a simple bias T.

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I’ve been testing the loop in the garden on the top of a 2M pole for the past few months. So far I have tried several transistor combinations. The original suggested BC547, BC549, 2N4401 and some 2N2222A. The 2N222A seem to be the best choice. They offer the lowest noise floor with good intermod and strong signal handling.

Over the next few days I’ll be installing the loop in the attic and attaching it to a rotator.



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