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Old September 10th 04, 03:55 PM
Jack Painter
 
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"Craig Buck" wrote

Two big advantages of the center top feed as opposed to bottom end feed is
center top requires no radials. Bottom L will need a minimum of 8 100

foot
radials in your application and some would argue you need many more than

8.
Have fun burying 800+ feet of wire. Second, top feed gets the high

current
radiating part of the antenna up higher. Check out
http://www.cebik.com/ltv.html and his discussion of ladder line at
http://www.cebik.com/gup/gup32.html. He concludes a 1:1 balun is best.

If you have 37 feet of height you can feed at the top and run the wire
straight down, back up and then down again for a total of 3x37= 111 feet

of
wire on the vertical side. On the horizontal just bend back at the end or
let the end drop down vertically. Sure it will have narrower bandwidth

than
a straight dipole but you have a tuner and you can't have a straight

dipole.
--


Hi Craig, Mr. Cebik says nothing about wrapping radiators back and forth
near each other as the earlier referenced url:
http://hamgate.sunyerie.edu/~larc/su...inverted_v.htm

Cebik does comment:
"Bending the horizontal arm far end down: If horizontal space is limited, a
common practice is to bend (or dangle) the outer ends of a dipole downward.
since the region is the high voltage and low current portion of the antenna,
the radiation pattern is least affected by modifying the geometry." -and-

"Like many wire antennas, the inverted-L will tolerate moderate alterations
of geometry to fit the space available and still yield good, if not peak,
performance."

each leg longer. According to Cebik if you can get 3/8s wavelength,
you

are
very close to the full performance of a half wave. Feeding at the

top
middle does not require a radial field to work.


It doesn't appear that Cebik intended to imply that 3/8~ off-center feed
would ever approach true1/2~ dipole performance, just that it would still
operate. These off-center-fed variations (of Carolina Windhams?) are
confusing, no matter how much wire they use. Remember I don't need an
all-band compromising performer like the T2FD or Windham, but a specific
performer on 2182 Khz, and hopefully at least through 4125 Khz. Doing this
with 70' of horizontal span and two vertical attachment points about 37'
high is the challenge I am asking for help with. I cannot run anything like
KGØZP does, which creates (in his location) a near-field coupling nightmare,
in my opinion. Your suggestion (doubling the verticals), which varies from
both the KGØZP design and Cebik's "moderate geomtery alterations", would at
least add electrical length, but it remains off-center-fed and therefore
never creates a 1/2~ dipole, correct?

If I stuck with a 1/4~ end-fed L, and only used 8 radials of 20-40', could
this still outperform an off-center-fed antenna off any length on 2182 Khz?

Thanks again for the comments and ideas,

Jack painter
Virginia Beach VA


 
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