MINI LOOP ANTENNA

80m - 160m mini loop antenna and details of the corner of the loop. The wires rest on the cut out ridges on the four spreader arms.
(Sides of the square are about 42cm)

This design is for a small loop (side length 42cm) suitable for receiving on 80m and 160m bands. Wooden spreaders were cut from HDF and their ends cut with groves to take the turns of wire. I used 7 turns wired to ca. 300pf capaciter. An additional single turn coupling coil goes to the coax for the receiver. A single complete turn did not match 50 ohm well and did not produce a sharp resonance. I tried feeding the single turn with 300 ohm feeder and using a 4:1 balun which was better. Finally I reduced the coupling coil to a small triangle (a fraction of a turn) and found it matched to 50 ohm well producing a much sharper responce.

As the loop is so small the SWR changes very considerably with changes of nearby objects (such as the opporators hand!) and positioning (e.g. moving the loop while nulling noise). As a result of this and its small size its probably not worth transmitting through this loop but it does work well for receiving. I found a ca. 300pf tuning capacitor made the mini loop resonate between 160m and 80m. I set the antenna on top of an empty large plastic storage container and moved it around for nulls.

A camera tripod (see photo below) allows for easy adjustment of the loop. Sometimes you have to both rotate and slope the loop to find a good null in the noise. It's a great little antenna and the null provides a wonderful drop in noise to bring in the DX!

I love listening on 80m in the winnter especialy at christmas times and usually spend a few days at my parents QTH listen at night or early morning while everyone else is asleep! I have tried many antennas at this QTH. This little loop got me listening on the SSB DX for xmas 2006. One particular evening I had a lot of fun listening to the North African EA9IE work the world (well a lot of North America)! The log-book entries show what I could hear on this little loop (inside the house from my second story room, location in Sussex, UK).

Typical 80m log-book entries using this mini-loop and a home-made direct conversion receiver / pre-selector:
(RS/T - my receiving strengths and tones given for the stations received from my location in Sussex, UK)

Date	Time (UTC)	Call	RS/T
22-12-06	23:22	EA9IE in contact with:	57
"	"	W1NA	56
"	"	KU4UN	53
"	"	K3GRT	42
"	"	W6UB	53
"	"	VA3XQ	52
"	"	W2VP	54
"	"	W4WTB	55
"	"	W5EU	53
"	"	WB4BNO	53
"	"	AK1N	55 strong!
"	"	KC1MAI	32
"	23:32	KV2AA (Vergin Islands)	55
"	"	N4NW	55
"	"	VA3JL	52
"	"	WA1T	55
"	"	K1LPS	53
"	"	W1VO	56 (SO STRONG!)
"	23:45	W1VJ	55

The mini-loop on tripod. Note weight to counter balance.

Links:
small HF loop

Some thoughts about the 80m band

back to G1EXG's Radio page

THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare, University of Sussex, East Sussex. BN1 9QJ.

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