Someone mentioned it earlier as I recall, but one of the reasons the G5RV
appears to have somewhat low SWR is the fact that the coaxial transmission
line and the associated balun are actually a "lossy line" section. Now a
lossy line has loss both ways, going to the load and coming from the load.
Thus any reflected power from the load is attenuated on its way back to the
transmitter or source. The net effect is an appearance of a lower reflected
power or lower SWR as we typically measure SWR at the source. Case and
point, a 250 ft. length of RG-58 with show basically a 1:1 SWR at the
transmitter regardless of what is connected to the other end. It can be a
50 ohm load, a short circuit or an open circuit or anything in between. The
result is that the section of line looks like its characteristic impedance
of 50 ohms to the source or transmitter.
I acknowledge the fact that thousands of hams are using the G5RV design and
successfully making many contacts and enjoy the fact that the single antenna
allows them to work all bands. The use of a tuner is either required or
advised and the tuners in the radios of today, having limited matching
range, do a good job of handling the load presented by the G5RV.
I have personally conducted tests in a controlled condition, measuring
patterns and field strength values of several HF antennas with the G5RV
being one of them. There is no question about it, the G5RV does not radiate
as well as the basic 1/2 wave wire that is center fed with a balanced feed
or low loss coax. In certain cases the data concluded that the field
strength was 6 to 9 dB less and in one data set some 12 dB less while using
the G5RV. From a ERP {Effective Radiated Power} point of view, the 100 watt
transmitter would then have a ERP of 12.5 to 25 watts. Still, we all know
that one can successfully work many stations and DX with only 10 to 20
watts.
73
Bob, K4TAX
----- Original Message -----
From: "Alfred Lorona" <w6wqc@dslextreme.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Saturday, January 31, 2009 10:49 PM
Subject: Re: [TenTec] G5RV
>A G5RV fed with open wire feedline and a tuner will work just as well as a
> regularly configured G5RV. The flat top wire does the radiating and it is
> the same length in either configuration so the results are the same. The
> advantage of the G5RV was that no tuner was required for the bands it was
> designed for. That one higher frequency 'problem' band is the cause of all
> the modifications and adjustments already described. The designer of the
> G5RV did not include that band in his basic design. The advantage of a
> simple dipole, resonant length or not, fed open line is a perfect 1:1 on
> any frequency on any band and you don't have to use coax anywhere.
>
> AL
>
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>
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