Big Doublet

This Antenna is no longer in use due to moving into town.It Worked Like Gangbusters, and I really miss It. It was 322 foot long and fed in the center with 450 ohm ladder line, and was about 30 feet up. The ladder line ccame down the side of the house and into the basement where it was connected to an SGC-239 . Then a 15' coax run up through the floor into the shack. It tuned well on all bands 160M thru 10M.

Sometimes while running QRP, the tuner would come unlatched and hunt, find a match and relatch, stay for a few minutes, unlatch, etc, etc. That was disconcerting since most QRP rigs dont have sophisticated power fold back circuitry to protect the final. Usually they employ a zener diode from the final's colletor to ground.

I surmised that rf getting into the tuner was causing problems. First I tried a better ground, closer to the tuner. That helped some but didn't eliminate the problem. The next step was to install a choke balun between the tuner and the feedline. That made the tuner was made much happier. Now it tunes near 1:2:1, and stays latched up....

The balun I used is the W5YR bead type choke balun This balun is cheap and easy to make, It is five 1-1/8 ferrite beads, type 43 material, Fair-Rite #2643540002. These are the right ID to slip over RG-8X coax. George Baker, W5YR (SK) developed and suggested this balun design in QRP circles. It may not handle QRO power for very long, but I think (no real data here) that its good for 50 - 60 watts, CW duty cycle.. At least it didn't get warm when I put 80 watts through it for 1 minute with 40 meter energy, and the tuner stayed latched up the whole time..

Revised 5 Dec 2012
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