Sunday, October 17, 2010

Copper cactus J-Pole - part 1

For some time I've been wanting to get a decent antenna up for 2 meters. We have a good technical 'net on a Monday night by the AHARS guys. I used to regularly join in but my little HT's batteries died and it doesn't work without them. I do have a little 1 watt Kenwood rig and a 4AH 12volt battery, which works a treat. However the antenna situation is letting it down. It works quite well on receive, but I need to get the antenna up much higher to activate the repeater.

Quite some time back, I was given some scrap aluminium and a 2 meter slimjim. I used the slimjim alot. It was pretty fragile and I repaired several breaks from wind damage, but its just not very practical as a portable antenna for the rallies, eg ROSA or as a home base antenna.

Lots of digging on the Internet yielded lots of info on the copper cactus antenna. I didn't have any of the common materials, so a visit to the local hardware stores didn't have any hard drawn copper pipe either. Well, Home Hardware had six meter lengths of 1/2" for $98 and did not cut off lengths either =( I decided that a copper cactus was going to be out of my reach and put it off.

Then I picked up a little dual band 2m/70cm 3/8" screw on to mag mount antenna for the car, just before the rally. Its ok pootling around on the car, but with out any ground, it doesn't perform on the little Kenwood at home as well on receive as the rubber ducky on the HT. Its pesky to setup and use at home.

That was all some eighteen months ago. Since then Bunnings has opened and some of their stuff is cheaper than the other hardware stores. Bunnings also has more range, but quality varies greatly. However, they did have 1/2"/15mm and 3/4"/20mm hard drawn copper pipe, but only in 1.5 meter lengths. The HDCP 20mmx1.5m is $16 a length, with 20mm 90 degree bends $2, 20mm Tees $3 and one bag of 1" clamps/brackets $7. So last weekend I needed to get some other things from Bunnings, so I got all the bits I needed and some spare for future projects.

This evening I worked out the measurements and cut up, then sanded the pipe, bend and tee joiners. I have a little industrial hair dryer, which gets everything up to temperature and soldered the lot up.

What remains is the mounting to little mast and getting some coax set up to the clamps. Obviously matching and endless tweaking =)

Can't wait to get the antenna up and tested.

72, Kim

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