Tuesday, March 11, 2014

Simplest antenna - open wire fed dipole

Spurred on by the ARNSW Antenna day, and illuminated by a comment from Mal, VK2BMS, that alerted me to the fact that I've been using my Emtronics EAT-300 tuner incorrectly; I had a go at the simplest antenna - a dipole fed with a slotted ribbon.

Cut for 10m, this tiny dipole is held out from the balcony on a 6m squid pole (the heavy half is inside so it doesn't fall off). The slotted 300 ohm ribbon was 30 cents a meter at Paddy's Market. I hold it away from the metal railing in a little string sling.

I've tried open wire feeder in the past but could never find a low SWR resonance point  - it turns out the EAT-300 tuner needs a link between the single wire terminal and one side of the balanced line. There's a dotted line printed on the box but I never understood what that meant.

I'm running 20W here but when I skeptically responded to a CQ call from Charlie, VR2XMT, in Hong Kong he immediately responded and gave me a 57 which is pretty good.

The open wire fed dipole seems much wider in bandwidth than a similar co-ax fed dipole.

Obviously, while an open wire feed works for me in a location where I can get from the antenna to the tuner without encountering much metal, it's not good for other antenna - shack arrangements.

Once again, using a squid pole to push the antenna out from the building makes a huge difference compared to being on the balcony with concrete and metal all around. I'm up high enough and the squid pole and antenna is thin enough to be virtually invisible from the ground.

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