[Elecraft] Balun with a G5RV?

Ron D' Eau Claire [email protected]
Sun Apr 21 12:06:03 2002


As several ops have pointed out, there are many variations of "center fed
doublets" called G5RV's out there. When Louis Varney developed his antenna
the standard "doublet" was a center fed wire 1/2 wavelength long on the
lowest operating frequency. Balanced feedlines were the standard of the day.
(One reference I have says that Varney first designed his antenna in 1946,
although it was 10 years before the design was published.)

What Varney did that was a little different from the common "doublet" was to
scale his antenna to be three half waves long on 20 meters, rather than
simply 1/2 wavelength long on the lowest band. That offered a somewhat
better compromise for a good radiation pattern on 10 meters and a of
impedances on the ham bands to make loading the antenna somewhat easier.

Since then endless variations have appeared to accommodate the fact that
coaxial cable has become the feedline of choice, transmitters now offer
unbalanced output instead of balanced outputs, and we've added a number of
Ham bands to our HF spectrum.

With these changes the issue of how to get r-f into a "G5RV" has become more
complex and the performance of the antenna is more difficult to predict.
Still, like its more common "center fed doublet" cousin, it can be a highly
effective radiator.

For multiband use, I have always preferred a center fed doublet using high
quality open wire line and a BALANCED antenna tuner. Sure, I have to twiddle
a few knobs that takes 30 seconds, perhaps, when changing bands, but I gain
perhaps 3 dB (doubling my output power) or more by a more efficient antenna
system and I can go anywhere in the HF spectrum with equal ease. Also a
center fed doublet (and so, too, a G5RV if the feeder losses are not
excessive) will work very well down to the frequency at which the doublet is
only 1/4 wavelength overall, meaning that a 66 foot radiator will work quite
well on 80 meters or a 120 foot radiator will work well on 160 meters if it
is high enough off of the ground.

But the popularity of coaxial lines and now the proliferation of automatic
antenna tuners has kept the "multiband" versions of the G5RV alive. Still,
the issue of a good combination of feedline sections to avoid excessive
losses is a complicated one. One good resource dealing with G5RV feeder
system design issues that I know of on the WEB is at
http://www.extremezone.com/~nk7m/ant4.htm.

Ron AC7AC
K2 # 1289