"Frank" wrote in message
news:JFqqe.44797$on1.7535@clgrps13...

"Cecil Moore" wrote in message
...
Frank wrote:
The nominal impedance of a 40 m dipole on 20 m, at 30 ft above an
average
ground, is
4700 + j0. There may be some inductive or capacitive reactance
present --
depending on the exact length of the antenna -- but it will not
effect
the
transmission line losses significantly.

100 ft of RG 58 exhibits a total line loss of about 13 dB when
terminated
with the above impedance. i.e. 100 W in gives 5 W radiated.

While 1/4WL (or 3/4WL or 5/4WL) of 450 ohm ladder-line yields an
impedance at the transmitter of 43 ohms for a 50 ohm SWR of 1.16:1
without a tuner and very low line losses. What could be sweeter?
--
73, Cecil http://www.qsl.net/w5dxp


I agree, but many people do not seem to get it.

73,

Frank

=======================================

Just out of curiosity I calculated the following details of 100 feet
of RG-58 terminated with 4700 ohms at 14 MHz.

Line input impedance = 12.3 - j37.7 ohms.
SWR vs 50 ohms at termination = 88.6
SWR vs 50 ohms at generator end = 6.35
Matched loss of 100 feet of line = 1.3 dB
Actual loss = 11.4 dB
With 100 watts input, output into 4700 ohms = 7.2 watts.

A tuner is essential. There will be additional loss.

By the way, at the first current loop, line current is 3.41 amps. As
the inner conductor diameter of RG-58 is only 0.78 mm, the temperature
of the pvc jacket can rise to about 20 degrees C above ambient. So
don't hold the line in the hand for too long.
----
Reg.