Frank wrote:
Put up 66 ft of wire, or any length that is convenient. Wire length is
unimportant. Inverted vee is ok. Feed it with open wire line (Or 450 ohm
ladder line) an any point you like. It will work just the same as a full
sized dipole.

EZNEC says that a 66 ft dipole used on 3.8 MHz, fed with 450 ohm
ladder-line, will have an SWR of greater than 100:1. This can
lead to all sorts of undesirable effects including an almost
impossible to match impedance at the tuner. A practical rule of
thumb might be in order, e.g. mine = no more than 20:1 SWR on the
ladder-line.
--
73, Cecil http://www.qsl.net/w5dxp

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EZNEC says that a 66 ft dipole used on 3.8 MHz, fed with 450 ohm
ladder-line, will have an SWR of greater than 100:1. This can
lead to all sorts of undesirable effects including an almost
impossible to match impedance at the tuner. A practical rule of
thumb might be in order, e.g. mine = no more than 20:1 SWR on the
ladder-line.

Fact is Cecil I never pay any attention to VSWR, just complex numbers.
Anyway your comments made me re-analyze the problem, and I realize I made an
error in the transmission line and antenna tuner analysis. I thought the
transmission line loss I came up with was a bit low. The final numbers are
shown below. See if you agree with me; then explain where I went wrong, and
why the match will not work.

66 ft dipole, 30 ft high, #14 AWG: Input Z = 11.3 - j961 ohms.
50 ft of 600 ohm line: Input Z = 5.48 + j189.85 ohms, loss = 1.95 dB
Matching network: Shunt C = 296 pF, Series L = 22.8 uH.
(Obviously half the L for each side of a balanced.line.)
Max line voltage: 1.5 kW in = 3 kV.
Tuner loss: 0.44 dB.

Incidentally have you ever looked at a typical airport NDB site? For
example a 45 ft monopole on 350 kHz has an input impedance of 0.2 - j7054,
which is a VSWR of 4.9 million : 1 -- whatever that means -- virtually
touching the edge of the Smith Chart. I have even seen 5 mile approach NDBs
with 30 ft monopoles. Marine installations for 400 to 500 kHz operation
frequently had electrically very small inverted "L" antennas. Of course 5
S/m sure helped, but the losses in the tuners must have been significant.

73,

Frank