Thank you very much John. I admit not giving two hours of learning time to
my EZNEC demo, but I wrote it off as too complicated to assimilate in the
time I could spend on it. That's an interesting finding on a "short" dipole
tuning up on 2182. I had not considered what ladderline to a dipole might
allow...

Jack

"John Moriarity" wrote

Hi Jack,

I usually lurk here quietly, but thought
I'd stick my neck out.

I just did a quick analysis on EZNEC.
Imagine a wire that is 50 feet up, 70
feet across the top, hanging down 40
feet on each end for a total of 150 feet.
Feed it in the center of the top with
75 feet of 450 ohm line.

The impedance seen at the end of 75
feet of 450 ohm feedline looked pretty
workable on both 2182 and 4125 kHz.
(Yes, you need an antenna tuner, but
it could be very simple for just two
frequencies.) An NVIS antenna like
this is great for short range (a few
hundred miles).

Download the demo version of EZNEC
from www.eznec.com . It'll take you a
couple of hours to get familiar with it,
but then you can play "what if" with
a lot of simple antennas like this.

73, John - K6QQ

Most of the info I got on linear loading comes from ON4UN's book Low Band
Dxing. It is a great source.

The top fed L I am describing is center fed. There is an equal amount of
wire on each side of the center insulator.

I just find this solution a whole lot easier than burying 800 feet of wire
to make a bottom fed inverted L.

--
Radio K4ia
Craig "Buck"
Fredericksburg, VA USA
FISTS 6702 cc 788 Diamond 64
"Jack Painter" wrote in message
news:cfj0d.178414$Lj.153426@fed1read03...

"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

"Richard" wrote in message
...

Best I could do:

10m 10m
------------------------------------------------
| |
| pole on house
| 10m
|
|
x feed

back garden front garden


or even better perhaps:

10m 10m
------------------------x------------------------
| | feed |
| pole on house |
| 6m | 6m
| |
| |

back garden front garden

Getting G5RV-ish now. Not that great for 160 though.