Bruce Array Antenna

Yes folks, it's time for the 6m 'Magic Band' to open once more.  Last year, the band was wide open around 13th May, so it's certainly time to listen-in again.

I've a trusty two element 6m quad from a while back that works very well indeed.  The only problem is that I haven't got a sturdy pole to keep it from turning slightly in heavy winds, so it gets battered a bit.

So I decided to revert to a wire array I'd seen in the ARRL Antenna Book but that's been around since at least the 1920s - the Bruce Array.

Bend some wire - get an antenna with gain!

Before you rush out to build one, remember this is a broadside array, not an end-fire one.  In other words, if you want to work south (and north, as it's bidirectional), the antenna's broad side needs to be pointing N-S.  If you're looking along the wire to the south/north, you've got it 90 degrees out of position!

This is a very simple antenna to make.  Just bend a bit of wire to make a series of loops, yielding as many quarter wave vertical legs as you think might be useful (you ideally need each side of the loops to be 1.05 x 1/4 wave in length.)  You get modest gain - around 5dBi or so, and the antenna scales to any band.

I threw up some old, repaired fibreglass poles as end supports, and strung two UV-resistant lengths of light rope between them as the catenary.  The measured wire (cheap and lightweight equipment wire from E-bay) was attached to the rope using cable ties at the bends, and some tape as back-up.  A fence post holds a piece of narrow timber at the middle, to support the weight of the dipole centre, which is fed with 300 Ohm twin to a 4:1 current balun.

Not exactly obvious - the 6m broadside Bruce Beam, aiming south.  Ideal for stealth deployment.

Without any cutting, the SWR came in at a maximum of an easily transmatched-out 2:1 in the whole 6m band.  Because I'd cut the wire to 1/4 wave and not 1.05 x 1/4 wave, the antenna was resonant at the upper end of 6m, so a little short.  Losses in twin are negligible, so a 2:1 SWR is more than acceptable if you don't want to add or cut some wire.

UPDATE.

Great excitement this morning!  Had some work to get on with, so set the rig up on 6m WSPR at 5W into the new Bruce Array.  I was amazed to find this strong signal from IK2JUA popping up so early in the day, at 08:24 UT.  Having scratched my head a bit, I wonder if this is a meteor reflection.  If you look closely, the signal does appear to start tailing off towards the end of the transmission cycle. The distances involved are too great for an aircraft reflection.  Most of the very few other UK stations on 6m WSPR also picked it up.