[Elecraft] Long wire antennas

[donovanf at starpower.net]

Hi Don, 


Of course you're exactly correct. 


The peak horizontally polarized radiation with respect to the axis 
of a long wire steadily decreases from 90 degrees for a 1/2 wavelength 
or shorter wire to about 50 degrees for a 1 wavelength wire, then 
very slowly decreases to 35 degrees for 2 wavelengths, 30 degrees 
for 3 wavelengths, 25 degrees for 4 wavelengths, etc. 


As the length of the wire increases, the direction of the main lobe 
for horizontal polarization more closely approaches the direction 
of the wire but in never gets closer than 15-18 degrees from the end 
of the wire for any practical wire length. There's always a deep null 
off the end of the wire for horizontal polarization no matter how long 
the wire is. 


If a long wire antenna is carefully designed and constructed to carry a 
pure travelling wave, the angle of the main lobe does NOT change 
relative to a classic long wire antenna; however, the amplitudes of 
the successive lobes can be greatly suppressed in a very carefully 
engineered antenna. Its extremely difficult to achieve travelling 
wave performance in a long wire antenna except for a few special cases: 
- a long wire with a resistive termination connected to a 1/4 wavelength termination wire, 
- a terminated rhombic antenna, 
- a Beverage antenna close to the ground, and 
- a resistively terminated vertically polarized half-rhombic antenna 
(sometimes referred to as an inverted-V antenna in professional antenna 
engineering circles). 


73 
Frank 
W3LPL 

----- Original Message -----

From: "Don Wilhelm" <donwilh at embarqmail.com> 
To: elecraft at mailman.qth.net 
Sent: Thursday, January 11, 2018 5:09:04 AM 
Subject: Re: [Elecraft] Long wire antennas 

Frank and all, 

While it is true that radiation off the end of a long wire is a deep 
null, The maximum radiation will be at an angle to the wire greater 
than 1/2 wavelength (less than 90 degrees). That angle will depend on 
the length relative to wavelength. 

A look at the radiation pattern of long wires and other Traveling Wave 
antennas will reveal that fact. The rhombic antenna and V-beams use 
that characteristic for their gain and directionality. 

73, 
Don W3FPR 

On 1/10/2018 11:40 PM, donovanf at starpower.net wrote: 
> Ron, 
> 
> 
> What you've come to understand is absolutely false except for the 
> special case of a long wire close to the ground. That special case 
> is called a Beverage antenna that radiates vertically polarized 
> radiation off the ends. 
> 
> 
> When you raise a long wire antenna more than about 0.05 wavelengths 
> above the ground, horizontal polarized radiation becomes dominant 
> and the radiation pattern always has a deep null off the ends. 
> 
> 
> 73 
> Frank 
> W3LPL 
> 
> ----- Original Message ----- 
> 
> From: "Ron D'Eau Claire" <ron at cobi.biz> 
> To: "Elecraft Reflector" <elecraft at mailman.qth.net> 
> Sent: Thursday, January 11, 2018 4:08:40 AM 
> Subject: Re: [Elecraft] Long wire antennas 
> 
> Understand that a true "long wire" (greater than 1 wavelength) starts to be 
> directional off of its end (if fed at one end, that's the opposite end). 
> 
> 73, Ron AC7AC 
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