Topband: 3/8 Wavelength Inverted-L

[Bill Tippett]

W0NFL wrote:

>I think we should listen to W1BB on the subject of inverted L 3/8 and also 
the inverted L 1/2 wave is also a excellent ant.  Why does the computer say 
the 1/4 L has a lower angle, maybe because the computer shows a perfect 
ground system with the 1/4.  

        Jim, the NEC model assumed the same ground for both.  A 3/8 wave
inverted-L with only 60' vertical is quite a diffentent beast from a true
3/8 wave vertical.  My 180' tower is nearly 3/8 wavelengths high and 
it has the following pattern characteristics compared to a 3/8 wl
inverted-L:

Antenna         Takeoff angle   3 dB Vert beamwidth       

3/8 Inv-L         90 degrees      22-158 degrees            
3/8 Vert          20 degrees      6.5-45 degrees

>I always thought the angle would go down until 
the antenna lenght would reach 5/8 wave and then go back up. I would think 
that still would work on bent vertical antennas from 1/4 up to 5/8 wave.  
Anyway back when chasing DX on 160 was tough in the 60s and 70s loran and 
power limits of about 100 watts out. the longer inverted Ls were outdoing the 
bent 1/4 verticals.  talk to some of the old timers on this.

        As ON4UN says in his book "...the longer the vertical part of the
antenna, the better the low-angle radiation characteristics of the 
antenna..."  A 60' 1/4 wave inverted-L is about 46% vertical while a
60' high 3/8 wave inverted-L is only 30% vertical, so it really works
much more like a low dipole than a vertical.  

        While we can all choose to believe anything we want, I have much
more faith in NEC models than anecdotes, war stories and legends...but 
to each their own.  Here is a brief summary of the NEC model which most
current antenna modeling software is based on:

"The Numerical Electromagnetics Code (NEC) has been developed at the 
Lawerence Livermore Laboratory, Livermore, California, under the sponsorship 
of the Naval Ocean Systems Center and the Air Force Weapons Laboratory. It 
is an advanced version of the Antenna Modeling Program (AMP) developed in 
the early 1970's by MBAssociates for the Naval Research Laboratory, Naval 
Ship Engineering Cneter, U.S. Army ECOM/communications Systems, U.S. Army
Strategic Communications Command, and Rome Air Development Cneter under 
Office of Naval Research Contract N00014-71-C-0187. The present version of
NEC is the result of efforts by G. J. Berk and A. J. poggio of Lawrence
Livermore Laboratory."

                                                73,  Bill  W4ZV