[Towertalk] 40m beams

[n4kg@juno.com]

A CC 3L40 seems appealing.

On a 36 ft boom, 1 dB additional gain could be achieved
with significantly higher F/B.

On a 48 ft boom, 2 dB additional gain could be achieved
with moderately higher F/B.

Gain rises very slowly from 0.35 to 0.75 WL which doesn't
justify a 4L parasistic antenna unless you want to side mount
a 48 ft boom (or less) and need more element clearance.

The best reason to go to 4 elements would be for improved
bandwidth using dual driven elements which makes sense
since 7000 to 7300 represents 4.3% bandwidth.

I believe CC has been asked about making a 3L40 
and they appear to not be interested.  Too bad.

Tom  N4KG

On Sun, 7 Apr 2002  "Jim White" <k4oj@tampabay.rr.com> writes:
> 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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> 


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