[TowerTalk] Stacking C-3 and EF-240S; EF-240S directivity

Pete Smith n4zr@contesting.com
Mon, 16 Nov 1998 12:49:43 +0000

Further to this topic, yesterday W9LT kindly came over and stood on the
boom of my C-3 at 100 ft, while pushing the EF-240S up to about 6 feet
above the tribander.  SWR on the tribander on 15M changed almost not at
all.  So then he rotated the 40-meter antenna 90 degrees.  That improved
the 15-meter SWR some, and changed that on 40 somewhat.  Reasoning that
this configuration is the least likely to have harmful interaction, we
decided to leave them at 90 degrees from each other.

It's funny looking, but back in the shack, the directivity on 40m on DX
seems definitely improved.  F/S ratio is ca. 25 dB and F/B is 10-12 dB,
about what I'd expect from 2 elements on a short boom.  So last night I ran
into EA5/M0AWR who has a 40-2CD at 75 feet, and we did some comparison
tests.  He confirmed the figures on my antenna, but I was amazed when he
turned his Cushcraft.  Front-side was closer to 35 db, and F/B seemed well
over 20 dB.  Granted, these are all TS-930 S-meter dB, but the better
pattern on the 40-2CD was obvious. 

I know that antenna has a 24-foot boom, and the elements are also longer
than on the EF-240S, but I was surprised at the difference.  W9LT says that
there has been some empirical work done that says lumped-constant loading
like Cushcraft's is inherently superior to linear loading.  I'd like to
know more, and also wonder what the gurus of Towertalk-land think of this.

PS -- I generated a huge pileup of weak Europeans on 40 last night, so I
know the EF-240S is working well.  Just wondering... 

Thanks all!

73, Pete Smith N4ZR

"That's WEST Virginia.  Thanks and 73"

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