[Antennas] G5RV/inverted vee: Radiation Angles

2003年1月10日 13:03:48 -0600

Pat's observations are well made. I would go a step further with the
comment that "G5RV" is an oxymoron, but that would make too many
enemies! <:}
A true 3/2 -wavelength 20-meter G5RV using the 20-meter half-wave
open-wire section and coax depends upon a fairly specific driving
point impedance for the "antenna" for the multi-band matching - such
as it is - to work. Varney designed the antenna to be a flattop.
Erecting it as an inverted-V not only changes the pattern but alters
the driving point impedance. Both the pattern and the driving-point
impedance are functions of center height and configuration.
What effects that would have are speculative since they depend upon
many unspecified and probably unknown aspects of the installation. But
that is the only difference that I can identify, apart from the
different pattern aspects of an inverted-V relative to a flat-top
dipole. Also, note the added vertically polarized radiation off the
ends of the inverted-V which is less with the flat-top format.
If the "G5RV" is simply erected as a 51 or 102 ft length of wire,
center-fed with ladderline to a tuner, then driving-point impedance no
longer enters into the discussion and any difference in performance
between inverted-V and flat-top configurations is attributed to the
pattern difference. There is no longer any point in terming the
antenna a "G5RV" unless somehow lengths of 51 and 102 feet have
earned permanent associated with that name.
But, it should be noted that unless the antenna is in the order of
1/2-wavelength high or higher at the lowest frequency of use, pattern
considerations are largely academic. The typical antenna mounted at 30
ft in the center and used on 80 and 40 will show little resemblance to
the textbook free-space dipole patterns. It is largely non-directional
in the azimuthal plane and concentrates its radiation more or less
vertically. Feedline variations such as the trademark G5RV half-wave
linear stub and coax, unless radiating due to common-mode currents,
have no effect upon the overall radiation pattern shape.
73/72, George
Amateur Radio W5YR - the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489 IC-765 #2349 IC-756 PRO #2121 IC-756 PRO2 #3235
----- Original Message -----
From: "Pat W" <[email protected]>
To: <[email protected]>
Sent: Friday, January 10, 2003 10:16 AM
Subject: Re: [Antennas] G5RV/inverted vee: Radiation Angles
> There is nothing different about the G5RV than any
> other dipole as far as take off angles at any height or
> whether it is in a Vee shape. THe lower the apex
> height, the more ground loss(less gain). THe steeper
> the Vee angle, the more vertical polarization.
>> PS: I'm not sure what a 'shorty' G5RV is. I think the
> term is an oxymoron.
>> Pat W0OPW