Well, the “magic band” is definitely open for business – summer means cricket on the radio and DX on six. Up until recently I have only had a rudimentary antenna set up for the six meters – very rudimentary in fact – my ½ wave vertical for 28 MHz, assisted by the antenna tuner. My attempts to build a ½ wave “bazooka” antenna for this band were a miserable failure, so I resorted to an old friend – the full wave loop, in a “delta” configuration.
Measurements for the antenna were made simple courtesy of KA1FSB’s webpage on loop construction (http://ka1fsb.home.att.net/loopcalc.html) which gave me the dimensions in metric. Parts for the antenna included two 3m lengths of aluminum tubing and suitable saddles to hold them down purchased from Bunnings; a length of copper wire, some plywood, assorted screws, ring terminals and a couple of U-bolts I had lying around; a ¼ wavelength of 75 ohm RG6 coax acquired at a previous Redcliffe club auction; a small project box, double SO239 line socket and PL259 plugs (one being made for RG213, which I used for the 75 ohm RG6) from Jaycar; and a length of 52 ohm coax to get back to my rig.
According to KA1FSB, each side of my delta loop had to be 2034mm in length (for 50.200 MHz), so I cut the aluminum and wire to the correct lengths. Next I cut my plywood to size (around 400x450mm) and laid out the tubing which I marked in place on the ply. I ended up with around an 80 degree angle for my pieces of tubing so that there would be a reasonable amount of tension on the top wire when it was attached. The plywood was weather-proofed with a coat of clear varnish. Holes were drilled for the U-bolts and the tubing was secured to the board using the saddles. I drilled the plastic project box so that the coax went in one end and the inner conductor and braid emerged from two separate holes on the top. After cutting the RG6 to size (my calculations worked out at 1414mm in length as a1/4 wavelength) the coax was inserted, insulation removed, conductor and braid pushed through and ring terminals attached. I soldered the PL259 (RG213 version) to the coax with some difficulty – aluminum wire braid, I assume, was the reason for my problem.
Time to put it all together! I placed the tubing on the ply and attached it using the saddles. A screw through one saddle on each side ensured that the tubing would be secure. Next the tubing was drilled at each end to attach the top wire and the coax, and these were attached. The project box was screwed in and my delta loop was ready for mounting on my mast…well actually a bit of water pipe on the fence, up about 4m, so attaching the light-weight loop with my U-bolts was no hassle. My 50 ohm coax was connected using the SO239 line socket and plugged into the rig. When finally it was all connected up, I held my breath and checked the SWR – yeeeha! Perfect first time – resonant and matched in one go.
The proof of the pudding is in the operation, so now I am using my new loop and seeing what reports I get. Recently working VK7 I received a 59+10dB report – blame it on the sunshine, moonlight or the boogey – my loop is working! In reflection, it was an easy project to construct, and being small it’s nicely incognito for the neighbours and the XYL. Hmmmm, I wonder if I can put another element on it and still be inconspicuous?
