Bill,
That is correct, but the currents on the 33 feet feedline should be
balanced and of opposite polarity - so they cancel. The current at the
radiator center will be less than that of a full size 80 meter radiator,
so it will be less efficient than a full size 80 meter dipole with the
current maximum at the feedpoint center.
There are numerous ways to phrase this, but bottom line is that a 102
foot radiator on 80 meters will not be as good an antenna as a full size
radiator. The current will be at a max at the parallel line to coax
junction, but will be reduced when the current magnitude reaches the
radiator.
Low SWR does not mean radiation efficiency.
Low SWR does mean the best efficiency for a match to a 50 ohm PA stage,
but the overall radiation efficiency depends on the antenna and its
feedline. One has to compute the losses involved as well as the current
into the antenna system.
Of course, I must say that if you can feed power into an antenna system,
that power will all be radiated (other than feedline loss). In the
example given for a 102 foot radiator, the balanced currents on the
feedline will not contribute to power loss - the current on that
balanced portion of the feedline will be greater than that presented to
the antenna, and the balanced feedline will be operating at an SWR
consistent with the impedance at that feedpoint.
As I have previously stated, there is little "magic" in antennas - the
principles have been around since the days of Maxwell and other greats
such as L.B Cebik W4LNR (SK) and John Kraus W8JK (SK) who have
substantiated those facts. Non-resonant antennas can be great
performers, but one must deal with the feedpoint impedances that they
present. Those two antenna gurus did not consider the matching problems
to their antennas, they properly presented the antenna radiation properties.
73,
Don W3FPR
73,
Don W3FPR
On 8/4/2016 8:34 PM, Nr4c wrote:
Let's see, 102 + 33 = 135. Isn't that pretty close to the length of an 80 Meter Dipole?
The G5RV looks like two back-to-back inverted "L" antennas. The twin lead is
not feed line but part of the radiator.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
