It is with some reluctance that I smack this whole EFHW tarbaby, but here goes.
Comments in no particular order:
1) A resonant antenna (even one that is self-resonant), e.g. one with a
non-reactive feedpoint, isn't necessarily "efficient." A quarter-wavelength
monopole over lossy earth leaps to mind.
2) A non-resonant antenna isn't necessarily inefficient. The ever popular G5RV
isn't resonant on the band of interest (20M) but when fed appropriately, was as
efficient as a resonant dipole.
3) Consider a BC band 1/2 wavelength vertical antenna. Does the station
designer say, "Well, this EFHW doesn't really doesn't need much of a
counterpoise, so I'll just throw a 100' long wire on the ground and call it good
enough?" No, he install 120 radials that are even longer than the ones he would
use under a 1/4 wavelength monopole. Devoldere in "Low-Band DXing, Chapter 9,
Section 4.3 says: "Here comes another surprise. A terrible misconception about
voltage-fed verticals is that they do not require either a good ground or an
extensive radial system.'" Later in the same section he says, "Therefore it is
even more important to have a good radial system with a voltage-fed antenna such
as the voltage-fed T or a λ/2 vertical. These verticals require longer radials
to do their job efficiently compared to current-fed verticals."
3) When you backpacking mountain goats say, "Hey my wire isn't a vertical, it's
mostly horizontal", I say, if your radio is sitting on a boulder or the ground,
it's a vertical and your wire-on-the-ground counterpoise proves it.
Wes N7WS
On 2/11/2017 2:33 PM, Ron D'Eau Claire wrote:
All efficient antenna systems are "resonant" (jX=0) but the shorthand often
used is "resonant" to mean "self resonant". That is true of any 1/4
wavelength long radiator (again our common shorthand is usually "1/4 wave
wire") or any multiple thereof worked against ground. It is also true of any
half wave length radiator or any multiple thereof. (Note that these are
electrical lengths, taking into account any surroundings including the
radiator itself.)
While self-resonant antennas do not present a reactive load to the source of
RF power, the value of R, the resistance, may vary widely. There is nothing
magic about the 50 ohm load most of our transmitters are designed for.
However, a half wave radiator fed at the center presents a resistive value
near 50 ohms when fed at typical heights above ground (in free space it is
75 ohms). Half wave antennas became very popular after WWII because 50-ohm
coaxial feed line became abundant and cheap on the "surplus" market and Hams
were taking steps to deal with needing to avoid interfering with the rapidly
growing number of TV sets in nearby homes, including the Ham's own living
room.
In the following decades, greater and greater demands on harmonic
suppression have led to Ham transmitters with output filters specifically
designed for a 50 ohm load instead of being able to match a wide range of
load impedances.
So we have now moved the wide-range output network that was in Grandpa's Ham
transmitter out of the transmitter and into what we call an "Antenna Tuner".
But, of course it does not "tune" an antenna at all. It's just a matching
network to be sure the transmitter is delivering power to a load close to 50
ohms and non-reactive.
73, Ron AC7AC
-----Original Message-----
From: Elecraft [mailto:[email protected]] On Behalf Of Wes
N7WS
Sent: Saturday, February 11, 2017 12:44 PM
To: Charlie T, K3ICH
Cc:[email protected]
Subject: Re: [Elecraft] EFHW
jX = 0
Sent from my iPhone
On Feb 11, 2017, at 1:29 PM, Charlie T, K3ICH<[email protected]> wrote:
Define "resonance".
Chas
-----Original Message-----
From: Elecraft [mailto:[email protected]] On Behalf Of Fred
Jensen
Sent: Saturday, February 11, 2017 2:40 PM
To:[email protected]
Subject: Re: [Elecraft] EFHW
Ummm ... A full-wavelength wire is not resonant?
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
-----Original Message-----
From: Elecraft [mailto:[email protected]] On Behalf Of
Lynn W. Taylor, WB6UUT
Sent: Friday, February 10, 2017 12:13 PM
To:[email protected]
Subject: Re: [Elecraft] EFHW
Just a reminder, folks.
If it's not a half-wave, then it's a non-resonant wire.
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