The Australian 1 metre loop 

By Werner Funkenhauser

Back in August 1988, I needed some filler material for my column "Mediumwave International" so I reprinted a previous article.
I finally got around to scanning this column article but I've only scanned the last page. It should still give you a good idea of the antenna's design and construction.
The article originally appeared in the July '85 edition of DX Ontario under "Antenna Projects" and came to ODXA courtesy of Michael Harla of Vineland, New Jersey. It really originated with Radio Australia. 

This is the same loop that allowed me to hear Buenos Aires-870, Quito-880 and Tahiti-738, not to mention numerous TAs and Pan American DX from my apartment location in Guelph, which is in southwestern Ontario. 

(At the end of this article you will find a view of a similar loop, presented by Radio Nederland)
  

Components 

2 plywood planks 140 x 100 x .5 mm 
2 softwood blocks 100 x 76 x 76 mm 
broomstick 
28.5 metres of wire (main) 
4.1 metres of wire (pickup) 
2 metres of coaxial cable 
500 pf tuning capacitor 
solder, screws, tape 
Tools 

Saw 
Screwdriver 
Soldering iron 
Construction 

Make shallow grooves at each end of the 2 plywood planks 
Join planks to form an "X" as in the diagram and strengthen the joint by gluing in blocks 
Fix the broomstick to the framework with strong screws (pre drill pilot holes to avid splitting) 
Bore 2 small holes at the bottom end of one of the planks 
Push one end of the 28.5 metres of wire through one of the bored holes and secure it 
Wind the wire around the framework, resting the wire in the grooves and keep the wire taut until 7 turns have been made. Now push the end of the wire through the other bored hole and temporarily secure it. 
Secure the tuning capacitor on the plank just above the bored holes 
Trim the 2 wire ends and solder one to the stator (insulated section) and one to the rotor (frame section) 
Take the 4.1 metre wire and starting at the bored holes corner of the loop wind it around the same path as the center turn of  the main winding occasionally wrapping or twisting it around the center wire until you have completed one full turn. 
Solder the ends of this turn of wire to the coaxial cable, one end to the outer braid and the other to the center conductor 
Mount the loop on a solid base which is strong enough to support the loop yet allows you to rotate it freely 
Tape the coaxial cable to the broomstick (as illustrated). The loose end goes to the receiver. Attach the center to your receiver's antenna and the shielded (braided) connection to receiver ground. 
What if? 

If your receiver doesn't have ground and antenna terminals make a platform of a  shorter plywood plank to act as a ledge for your radio (above the cross arm joint or running the entire length along the bottom). Place the radio "inside" the loop upon this ledge. The antenna's signal will be inductively coupled to your radio. With this arrangement, you can do away with the 4.1 metre winding. 

If you can't get a hold of a 500 pf variable capacitor use one salvaged from an old BCB 5 tube (All American Five) receiver. These have dual sections. Solder the stator (insulated section) tabs together for maximum capacity (140+270=410). If there are mica trimmers, loosen the screws as mach as allowable. You may just get near the 500 pf you need. If this arrangement doesn't allow coverage of the entire band, have a look at the circuit supplied with the Radio Nederland's Loop Antenna . 
You can use a 365 pf capacitor with the RN circuit. These are available from  the Xtal Set Society. 

A couple of notes 

This is the basic loop that I've used since shortly after it appeared in DXO. I've built three copies and modified each one a little.. The current version is built with exactly the same dimensions but includes minor changes listed below. 

The main winding is of RG58 coaxial cable with inner lead shorted to the outer braid. With the heavier wire, I've needed to make the cross arms a bit stronger than those described. 
I've placed a 5000 ohm potentiometer in series with one of the leads feeding the receiver's terminals. This was done to level signals from the loop against a longwire when using a loop/longwire phasing combination. However with the loop used solo, the control acts as a sensitivity or Q control. A 365 pf capacitor may be used with similar results. 
Best coupling (pickup) between windings occurs when the pickup coil is mounted 1 inch below the main windings instead of being wrapped about the center conductor as described. This is easily accomplished by inserting the pickup wire through small holes drilled about 1 inch from the bottom of the center groove described on the grooved ends of cross arms.