[Elecraft] EFHW

[Ron D'Eau Claire]

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:elecraft-bounces at mailman.qth.net] On Behalf Of Wes
N7WS
Sent: Saturday, February 11, 2017 12:44 PM
To: Charlie T, K3ICH
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] EFHW

jX = 0

Sent from my iPhone

> On Feb 11, 2017, at 1:29 PM, Charlie T, K3ICH <pincon at erols.com> wrote:
> 
> Define "resonance".
> 
> Chas
> 
> -----Original Message-----
> From: Elecraft [mailto:-bounces at mailman.qth.net] On Behalf Of Fred 
> Jensen
> Sent: Saturday, February 11, 2017 2:40 PM
> To: elecraft at mailman.qth.net
> 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:elecraft-bounces at mailman.qth.net] On Behalf Of 
>> Lynn W. Taylor, WB6UUT
>> Sent: Friday, February 10, 2017 12:13 PM
>> To: elecraft at mailman.qth.net
>> 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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