[Towertalk] 40m beams

[Jim White]

Every so often this topic re-surfaces...so, I will take the turn this
time...

The 40-2CD works very very well...

I really would love to see someone develope a 40-3CD or 40-4CD based upon
it...

It seems a simple matter but nobody has ever done it...what is the "hard"
part of this endeavour?

It would seem that with computer modeling everywhere many must have modeled
the 40-2CD - whilst playing with their modeling has anyone added an element
or two to the design?

A true full size forty is of course a dream but - a downsized 40 is more
realistic.

Jim, K4OJ




----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>
Sent: Sunday, April 07, 2002 3:52 PM
Subject: Re: [Towertalk] 40m beams


> On Sun, 07 Apr 2002 14:35:16 -0400 Pete Smith <n4zr@contesting.com>
> writes:
> > At 06:11 PM 4/7/02 +0000, Barry Kirkwood wrote:
>
> > >Sometimes wonder if the 40m reflector is worth the trouble and
> > would be interested to hear from anyone who has moved from
> > single element to  two element combination ( or vice versa)
> > (ZL1DD)
>
> A 40M rotary dipole is a very effective antenna, especially
> when placed above 70 ft high.  There is a lot of benefit to
> be derived from having horizontal elements (as opposed to
> inverted vee elements) placed high and in the clear.
>
> I worked my first 300 countries on 40M using various
> rotary dipoles at 80 ft.  My CC 2L40 shows a perceptible
> gain over my other dipoles.
>
> > I made this transition, and I think Barry has a valid point.
> > Certainly,  the jump to a rotary dipole made a big difference
> > in my ability to  put a  signal where I wanted, and the
> > front-to-back ratio of my EF-240S  (essentially the same
> > as the 40 meter section of the C-4SXL) is not  impressive.
> > (N4ZR)
>
> Here are the ELNEC results for a free space 2L Yagi design
> using a reflector spaced 0.15 WL behind the DE for max gain,
> max F/B, and minimum SWR.
>
> Max Gain 6.95 dBi
> F/B 6      dB
> Feed Z 27.4 Ohms
>
> Gain 6.12 dBi
> Max F/B 13    dB
> Feed Z 44    Ohms
>
> Gain 5.58 dBi
> F/B 10    dB
> Min SWR 51    Ohms
>
> Note the low F/B ratios for 2L reflector Yagis
> and the loss of gain as the feed impedance is
> raised to match 50 ohm coax.  Maximum gain
> designs almost always result in a low radiation
> resistance at the DE which requires some sort
> of matching network.  Most split dipole fed Yagi's
> have less than optimum gain which is the price
> you pay for a direct 50 ohm feed.
>
> Tom  N4KG
>
>
>
>
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