|Here is the beginning of an article on the G5RV
supported as an inverted-V. There are some real surprises and the best way to
show what happens is to use detailed antenna patterns and 3D plots to
demonstrate changes. This book is generously illustrated with similarly
detailed patterns and plots to make examples clear and concise.
|5. "Can your G5RV be mounted as an inverted-V in
your opinion? I have seen it mentioned elsewhere - is this valid; are there
| I used to say there were no problems configuring a G5RV or any
other multiband antenna, for that matter, as an inverted-V. That advice
has now changed. Unless my computer is having a really bad day, I have
uncovered something very distressing. I have to say, from what I have just now
determined, configuring a G5RV as an Inverted-V with an included angle between
legs anywhere near 90-degrees is disastrous. I have put the patterns from the
models I have just constructed at the top of this page. I will explain what is
shown in these radiation patterns. The conditions for these models are simple.
||The height of the antennas is 50 feet
above average ground. The same antenna is used in both tests, only the legs are
lowered to form an inverted-V angle of 90-degrees. There are no other changes.
I will repeat this test at larger angles and report what I find. This
information impacts greatly on many antennas, so I may have to do some
rethinking and put in some serious antenna modeling time to determine just what
I've found. Stay with me. This could be something really important.
|Figure 1 - This plot
shows a G5RV in its normal flat top configuration. Superimposed is the pattern
of a 20 meter dipole at the same height.
||Figure 3 - For confirmation, I have included the
elevation pattern for both the flat top and inverted-V configurations. As you
can see, at useful takeoff angles, the G5RV's pattern is just about the same as
that of the 20 meter dipole.
|Figure 2 - Everything is the same as Figure
1, except the G5RV in now bent into a 90-degree inverted-V. The nice
six-lobe pattern is gone. As you can see, we have lost nearly 8 dB in signal
strength. The takeoff angle in these examples is 15-degrees.
||Figure 4 -
This is disaster. The nice, low-angle lobes are down nearly 8 dB. This is an
incredible amount of loss.
|I have take the process a step further to see what was happening on other
bands. This would confirm my original observation. Here is our standard 102'
G5RV operating on 15 meters. in this pattern, the antenna is supported as a
flat top. The pattern is about what you might expect. It's a multi-lobe pattern
with gain in several directions. The 3D plot resembles a butterfly.
|In the pattern at left, I have dropped the ends of our G5RV to form an
Inverted-V with an angle between legs of 140 degrees. The pattern is already
changing significantly. The four major lobes have retreated indicating a loss
of about 4 dB in low angle signal strength. The high angle lobes have now
combined into a very large double-humped lobe aimed directly upward. All this
is the result of dropping each end of the antenna only 20-degrees fro
The Inverted-V G5RV's problems only get worse.
|Note: The actual pages from the book are
similar in appearance. I had to reformat the pages slightly to accommodate a
web format without scanning in the actual page. Had I scanned in the original
pages, a lot of detail would have been lost. What appears above is very close
to the original.
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