[Elecraft] G5RV

[Stuart Rohre]

A thing to keep in mind about the G5RV is that it was intended for 20m
optimally.   Later authors, in as stretch, tried to make it something else
on many more bands.

As it goes above 20m, it has multi lobe patterns which favor some directions
at the expense of others.

Although I dearly loved my ZS6BKW varient of the G5RV; (a WARC band capable
one); L. B. Cebik has shown in studies that if you want the most chance of
working DX, you would pick an antenna with equal lobes in most of the
directions, like a single band dipole.   For multi band use, he found that a
parallel line fed, 88 foot doublet, has two main lobes like a dipole across
more bands.  The use of parallel line feed and a tuner lets you go where you
want in the bands, with low feeder loss.

No balun, and its attendant weight is needed  at the feedpoint; that is done
at the tuner.  You can use a tuner with a good internal balun, (usually
4:1); or use an external 4:1 Van Gorden balun to the coax output of Tee
tuners.   Some use a cable choke at the coax output:   A short length of
straight coax with several one and a half inch coax beads over RG58 cable to
attain a block to RF currents coming off the feeder and getting onto station
ground makes an effective choke.

When one goes back to the original Varney paper (which was before WARC
bands), (and in a time of 600 ohm lowest loss open wire feeders), you will
see that Varney assumed that some antenna length
"make up" was performed by the wide spaced feeder's upper section.  In terms
of the wavelength at 20 m, that was doubtful in his day, but never
challenged.   I am certain that modern interpretations of the antenna using
450 ohm line (ladder line) as I did, or 300 ohm line as some advocated,
could NOT "make up" any antenna length in the close spaced feeders with
their canceling waves.

Thus, at best, you have a 102 foot non resonant wire, requiring a tuner.  It
gets at best, in the ZS6BKW low version, a 3:1 SWR on 15m, (beyond what some
rigs can do).  Thus, there is some logic in advocating the shorter 88 foot
doublet as W4RNL, L. B., did, since you are non resonant and need a tuner in
both cases.   Our club has had a commercial G5RV which has required
reconstruction about four times because of the weight of a cable choke put
in line with weighty ferrite beads in the factory design.

Recently we set up a loop completely fed with 300 ohm line, and without a
cable choke at the feed point or shack ; and only a balun in the tuner.   No
trace of RF in the shack has been seen.   I would not use a balun at the
antenna feedpoint with a G5RV, nor did I when I built the ZS6BKW type.
With that one, I even operated 40, 20, and 15 without a tuner!   The band of
least performance was on 15, probably not because of the 3:1 SWR, as much as
the lobe pattern that fragmented badly on that band.  My feeder beyond the
stub, was RG 8x coax 65 feet long to the shack.

The 88 foot doublet will fit most any home lot, the 102 foot stretches it in
some cases.   In both antennas, you either need to provide a way to bring
off the parallel line from the center.  In a G5RV, you will either need it
up 40 feet, to take care of the 40 foot matching section; or you have to
bring off the matching section horizontally, with a back stay guy to counter
its weight and pull on the alignment of the center of the doublet.  That is
what I successfully did in creating the "K5KVH" from the ZS6BKW varient.  In
the 88 foot doublet, you do not need any special length of feeder, so bring
it off at right angles, either horizontally or vertically, until clear of
the doublet area, then direct to the shack.

You can cross window sills (even metal) at right angles with little effect
on the antenna feeder.  Use some cushioning foam insulation as the line
crosses any metal or sill.   Or, simply put a wall penetration conduit in
such as used for TV lines, (sold for years at Radio Shack).  Even simpler is
to drill two thin holes at feeder spacing for all thread bolt material.
Sleeve it with shrink tube where it is inside the wall, and make sure there
is no metal siding or studs nearby.   Put insulating washers on each end of
the all thread, and then nuts and washers to attach your parallel feeders.
Such a penetration of wood or even masonry walls is easily patched with
spackling on the interior wallboard, and concrete patch on exterior if you
move.  This should be adequate for 100 watts and you can make special entry
panels for full limit rigs.

72,
Stuart Rohre
K5KVH