1. The G5RV Antenna
Although the
popular G5RV antenna is often promoted
as an antenna that works well on all bands from 80 through 10 meters,
that is absolutely NOT the case.
This is not to
say that the G5RV doesn't work well on SOME bands. But it does
NOT work well on ALL HF bands. That's my
point.
There are some
bands where the SWR on the coax is out of
sight and the feedline losses are astronomical.
2. The ZS6BKW Antenna
Depending on
which bands you want to operate, there is a
better design which involves shortening the antenna and lengthening
the section of ladder line. G0GSF (ex-ZS6BKW) came up with a similar
design that is
a significant improvement over the G5RV.
Even that design
still doesn't cover all the HF bands
The
ZS6BKW's top
section is 93' (instead of
102'),
and the 400 ohm ladder line matching section is 39.8', (instead of 30.6').
Before
you buy
or build that G5RV, do yourself a favor and Google g5rv ZS6BKW|G0GSF.
To summarize:
- Neither the G5RV nor the ZS6BKW antenna works on 30 or 60 meters.
- The G5RV does NOT work well on 17 or 10 meters. The SWR is a
little better on 80 than the ZS6BKW.
- The ZS6BKW does NOT work well on 15 meters, and needs a tuner to
work well on 80.
3. The W0BTU
Antenna
Our
modification to the G5RV and ZS6BKW antennas, while also somewhat of a
compromise of frequency ranges and VSWR, lets us use all HF bands between 80 and 10 except 30
and 60* meters.
EZNEC
file for the W0BTU version, which uses a 97' straight top section, a 39.5"
length of "450 ohm" (usually, the actual Z is 420 ohms) window line, and 75 ohm coax feedline.
You can tweak the lengths slightly to suit your height, operating
preferences, etc. The design height of these SWR plots is 40' above
ground.
Frequency vs. SWR
plot
(3.5-29.7 MHz.)
The above bands can be used without switching the feedline, just like
the ZS6BKW antenna.
However, removing 8.5' so that the length of the open wire line is 31' lets this new
design also work
well on:
The W0BTU antenna covers more
bands than either the
G5RV or the ZS6BKW. A simple DPDT knife switch (or banana plugs and
jacks) near ground level lets us use 75/80 and 15 meters, if desired.
Even though the VSWR is relatively high on 75 and 80 meters, lower coax
loss on that band at least lets us operate there using just one
multiband antenna.
NOTE: The remaining 8.5' section is not connected in any way on 75, 80, or 15 meters. It
must be totally removed from the feedline. If one end of it is left
connected, the antenna doesn't work right.
* Well, it will work on 60 meters, if you use a 76' length of the 420 ohm window line; SWR is below 1.5:1.
Note that the
SWR values in the above charts are at
the antenna.
Some commercial
G5RV antenna designs rely on the loss in a long coax feedline to bring
their
claimed SWR down in lieu of—or in addition to—an antenna
tuner.
