Re: [IRCA] Reversible Double-Delta

["Mark Durenberger" <Mark4@xxxxxxxxxxxxxxx>]

By the bye: 690 Minneapolis, 25 miles away with 4 watts authorized 
post-sunset came in at -36 dbm (its day level) and never changed through the 
evening, well past sunset.


Regards,

Mark Durenberger


-----Original Message----- 
From: Mark Durenberger
Sent: Sunday, May 18, 2014 10:13 PM
To: MNDXC ; DX @NRC ; DX-IRCA ; Shafer Mike ; Baumgartner Fred-ARRL
Subject: Reversible Double-Delta

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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