G5RV Antenna

[w7aqk]

-----Original Message-----Jim, the original G5RV is a 1-1/2 wave 20 meter
*only* antenna that offered
a good match for the coaxial line by using an open-wire matching section. As
you know, such matching sections are frequency-dependent, like any fixed
tuned matching network. The G5RV allowed the use of the newly-available (at
affordable prices) coaxial lines that appeared at the end of WWII.

Louis Varney (G5RV) contributed to the discussion of using his 20-meter
"G5RV" on other bands. That's what causes a lot of confusion.

At the time Varney published his original design, many Hams operated on only
one band.

That changed dramatically in the years after WWII, particularly in the
1950's. The rapid availability of surplus parts and entire rigs, a rather
affluent post-war society here in the USA, and a large number of commercial
and kit rigs appearing on the market in the 50's made multi-band operation
"normal" for most Hams.

Hams, always willing to "try anything" for an antenna -- even loading up the
bedsprings (literally!), wanted to use Varney's G5RV design on more than 20
meters. Of course, the G5RV is nothing more than a doublet fed with open
wire line, an efficient multi-band design that had been popular since the
1920's. Varney's contribution was the use of a specific open wire line
section to match to coaxial line on 20 meters without the need for an
antenna tuner (ATU). Ignoring the matching section and simply using it as a
multi-band doublet worked fine, as long as one used a suitable matching
network (ATU) and avoided the coax section.

The problem was that Hams wanted to use coaxial lines. Not only were they
easier to run into the shack, virtually all post-War rigs were designed for
coaxial feedlines for simpler bandswitching and TVI-proofing. So the battle
to find a suitable compromise between efficiency and the use of coax in a
multi-band "G5RV" started in earnest.

Varney himself wrote about those attempts, emphasizing the need for a
matching network (ATU) on any but the 20 meter bands or if the dimensions of
the antenna or feeders were changed in any way.

One of those taking up this challenge was ZS6BKW who wrote a computer
program to study and optimize the best combination of length and feeder for
a G5RV-like antenna. His design provides a decent (<2:1 SWR) match on 7, 14,
18, 24 and 29 MHz but shows quite high SWRs on 3.5, 10, and 21 MHz.(see
"Practical Wire Antennas" by John D Heys, G3BDQ, published by the RSGB, page
22).

Ron AC7AC

---------------I think Ron has pretty well summarized my understanding of
the problems and pitfalls of using a G5RV antenna.  It is greatly overrated
from most everything authoritive I have seen.  Some years back, Bill Orr,
W6SAI, also wrote an article which extensively described why a G5RV isn't
all it's cracked up to be.According to Orr, the SWR on some bands is very
high, if not excessively so.  A tuner is pretty much mandatory in his view,
as it was in Varney's view after the modifications to his design were made.
You'd be much better off just feeding the antenna with balanced line and a
tuner, and possibly even shortening it to 88 feet as suggested by L.B.
Cebik.Dave W7AQK


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