If two 20m wires are better than one 40m one for the same total lenght of
wire , Does this mean that four horizontal legs of 10 m would be even better
? and so eight of 5m or sixteen of only 2.5m better still ?
How about
64 X 625mm ? or......
just a disc of foil 1000mm dia.?
Perhaps there is an optimum number of horizontal wires?
If just a 1000mm disc then why not have one at the bottom instead of earth?
Why does the name Hateley come to mind ? ;-)
Bryan
Bryan G3GVB
----- Original Message -----
From: "M. Sanders" <[email protected]>
To: <[email protected]>
Sent: 01 January 2004 01:50
Subject: RE: LF: Re: "T" versus "L"aerial
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 <mailto:[email protected]>
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
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