A Plumbers delight receiving loop for 75 Meters

Here is another shielded loop antenna I built to help with the grow house noise on 75 meters. I call this type of construction "plumbers delight" becaue it is built entirely from the plumbing department of your local hardware store. It works a little better than the shielded loopstick described below. Being outdoors it gets a better signal and is farther away from AC wiring and noise sources in your house. It is fixed tuned for the AM window and basically impossible to retune without opening up the box. It is now sealed with silicone and is still clamped in the vise. The nulls are very sharp and can greatly reduce noise coming from a fixed source.

 

It is constructed from 1/2" aluminum tubing a couple of compression fittings and a brass T. One of the compression fittins is for 5/8" tubing. A short piece of plastic tubing is slipped over the aluminum tubing to insulate it. The loop is one turn of #14 wire 2.5' in dia.

Here is a close up of the insulated end. A plastic ferrule would be better but they are hard to find here behind the Redwood Curtain.

The T is supported by a copper sweat fitting that has been silver soldered to a brass plate and screwed to the top of a cast box.

The loop is tuned with about 400pf  and matched to 50 ohms by two 4:1 broadband RF transformers cascaded for a 16:1 impedance ratio. These are mounted inside the box.

This antenna for most will be easier to build than the shielded loopstick. It has a much lower output due to no preamp, but my old NC-303 has plenty of gain so it really does not matter. As long as you can hear noise when the antenna is connected, thats all the gain you need.