[IRCA] Reversible Double-Delta

["Mark Durenberger" <Mark4@xxxxxxxxxxxxxxx>]

This evening, 3 Phools in the Phield set up a reversible 140-ft. 
Double-Delta antenna at a quiet place in Burnsville MN.  The goal was to see 
what sort of nulling we could do off the "backside" of the antenna (whether 
the "backside" was the North end or the South end).  Think of it as a 
super-hot loop antenna, but unidirectional in pickup rather than 
bi-directional.

It works.

On a number of frequencies we were doing armchair copy of one station; flip 
the antenna and the first disappeared while another came up just as 
well...from the opposite direction.

We were oriented North-South since most of our local pests were North of us.

Antenna reversal is as simple as flipping a switch.

Interestingly...the null held up across the band; little or no re-nulling 
was needed.

Surprisingly, we could do no better than about 27 db nulls of local 
stations.  Our conclusion was that the Double-Delta seems to like low- and 
medium-angle skywave and doesn't discriminate as well with strong 
ground-wave signals.

We will also investigate whether the extension of the null pot and RF 
takeoff VIA UNEQUAL LENGTHS OF CAT-5 degrades the null.  (I've seen better 
than 40 db null on these guys when the null pot is right at the leg of the 
antenna; in this case we had run 150 ft. of Cat-5 to get to the receiver.)

Mike Bates and Jim Dale may chime in with their own observations.  It was an 
evening well-spent.

Regards,

Mark Durenberger, CPBE


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