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Hi All,
When I first set up my 136 station I put up a
Marconi "T" vertical ant. 15M high 30M long.The best ant. current I
could get from my 400 watt amplifier was 1.8 amps.The measured ground
/coil/copper loss was 125 ohm! Over the past 6 months I have tried to improve
this, I have increased the top to 3 wires,increased the grounding from 2x4 foot
rods plus house wiring/water etc to 10x 4 foot rods, 20 radials each about 50
feet long plus one radial 150 feet long ending up at an earth rod in sea water!
I also re-made the loading coil with thicker wire.The total result of all this
effort was 2 Amps !!! Not very encouraging.This weekend I decided to start
again.I replaced the "T" with an inv.L using the same support (tree)
at one end but 60M long to another tree.SO I now have less wire in the air 60M
instead of 3x 30M but stretched out.The loading inductance has not changed so
the capacitance is the same. BUT the ant current is now 3 Amps!
Does this mean that the antenna wire needs to
have a longer "footprint " on the ground?,presumably the current
density is less than under the 3 wire top,but the new ant stretches beyond my
radial system,and it is still much better!.Does this also explain the
reported good performance of so called "long wire"
antennas on this band?
Food for thought.
I am hoping to
improve things further but I dont have room to
extend the top wire in a straight line,perhaps I will try a crooked L
Hi.
Checks with Eznec indicate a R.Res
of about .06 ohms for the "T " and .0675 for the "L"
so with the increased current I hope to have improved my signal by at least
3db.
73s Laurie.
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