Dear
Dick / Bob and Lofers,
Does
the computer calculate the earth losses in the return path from the aerial
system to the transmitter? If it would then the earth losses in a T should have
been significantly less then the L alternative. There are two separate return
currents
(parallel resistance) and each with a smaler physical length (lower R-earth) in a T system
resulting in more ERP if compared to an L system.
Greetings
and best wishes for a (LF) radio-active 2004 to All.
Mike,
PC4M (ex PA3BSH)
-----Oorspronkelijk
bericht-----
Van:
[email protected] [mailto:[email protected]] Namens Dick Rollema
Verzonden: maandag 29 december
2003 16:37
Aan: [email protected]
Onderwerp: Re: LF: Re:
"T" versus "L"aerial
To All
from PA0SE
Bob, ZL2AC wrote:
Dick PA0SE,
Fine
on the test result. As you stated, the tested T has twice the amount of
top loading wire (2x 20 metres) than the L (1x 20 metres).
It
would be interesting to know if a T is better than an L for constant length top
loading i.e. what the difference is if the upwire joins at the end or the
middle of the horizontal top wire (theory suggests the T is better as there is
minimal horizontally polarised component).
Bob, I cannot answer your question by a
practical experiment but used computer simulation instead by means of K6STI's
program Antenna Optimizer.
I modeled two antennas with a vertical
element of 20m. One an Inverted L-antenna with a horizontal top load wire
of 40m. The other a T-antenna with a top load of 2 x 20m.
Both antennas without losses, over perfect
ground and fed with 1kW.
At a distance of 10km (so well outside the near field region) and over perfect
ground both antennas produced a vertically polarised field of 29.9mV/m. The
horizontally polarised field was zero; but this is to be expected because over
a perfect conducting ground a horizontal field component cannot exist.
73, Dick, PA0SE
Original message:
To:
LF-Group
Sent: Sunday, December 28, 2003 3:09 AM
Subject: LF: "T" versus "L"aerial
To All from PA0SE
Further to my e-mail of
26 December I measured the field strength as radiated
by the aerial in
Inverted L-configuration. From this I found EMRP = 57 milliwatt.
This confirms the benificial effect of top loading.
The T-aerial radiated 140
milliwatt.
So going from a single 20m top load wire for the
"L" to 2 x 20m for the "T" resulted in an improvement by a
factor 2.46 (3.9dB) in radiated power.
The vertical part of the "T" consisted of an
open wire feedline of 11m with the two wires connected in parallel in the attic
shack. For the "L" one of the feedline wires was removed. I assume
this did not appreciably affect the EMRP.
73, Dick, PA0SE
