G5RV vs 80M dipole
David Nye
Is there any difference in performance between a G5RV and 80M dipole or is
the only difference that the G5RV is a little shorter?
David Nye, KB9PSL * Eau Claire, WI
Dan Richardson
Hi David,
As the ½ wave dipole is larger it will theoretically have a higher
efficiency and gain, however, in practice it is doubtful that you
could detect any difference in operation between them. Given, of
course, both antennas are install in the same manner.
I sure Cecil will have something to add to this.
73
Danny, K6MHE
Cecil A. Moore
Dan Richardson wrote:
> I sure Cecil will have something to add to this.
Hi Danny, I hate being predictable. :-) The basic problem with a G5RV
on 75m is that the SWR is too high to get a 50 ohm match at the
current maximum point. Even at the 75m resonant frequency, the 50
ohm SWR is around 4:1 or so because the impedance at a current
maximum point is around 12 ohms. So an antenna tuner is necessary.
I've extended my 102 ft dipole to 130 ft because I can then eliminate
the antenna tuner. See my web page at:
http://people.delphi.com/CecilMoore/mystery.htm
73, Cecil, W6RCA, OOTC
Robert Lay
David Nye wrote in article <2.2.16.19970805...@uwec.edu>...
>Is there any difference in performance between a G5RV and 80M dipole or is
>the only difference that the G5RV is a little shorter?
>
>David Nye, KB9PSL * Eau Claire, WI
>
I think, based on common sense only, that there is perhaps 25% less signal
radiated on 80 m by the G5RV than the 80 m dipole. When you translate that
into db or fractions of an "S" unit, you will have what I consider to be an
insignificant difference. However, the angle of radiation, which is more
related to height above ground, is perhaps more important. That is, a G5RV
at 65 feet height might very well outperform a dipole at 40 feet height.
The real tradeoff with the G5RV is that it does reasonably well on all bands
80 through 10 m, and it does so without traps and doesn't require balanced
lines coming into the shack ( the original G5RV design did not use coax and
called for balanced feedlines coming into the shack and a balanced tuner -
see p 7-20 of ARRL Antenna Book, 17th Ed.).
Don't lose sight of the fact that the G5RV was really designed for 14 MHz,
and that accounts for most of its design parameters.
I have had no problem tuning a G5RV to the 30 m band, in spite of the
people who claim you can't get a match. It all depends on whether or not
you have a roller inductor tuner and are willing to make the coax a little
longer or shorter, as necessary. A tuner of some sort is generally accepted
as a "must" for the G5RV (See p21 of Practial Wire Antennas by John Heys,
G3BDQ).
You can make a G5RV yourself for less than half of the commercially made
ones, and at that price you can't afford not to try it.
There is much quibbling over the length of the 30 to 34 foot matching
section of the G5RV. It was originally intended to be a multiple of a 1/4
wavelength at 14 MHz. The reason for the different lengths in the various
incarnations of this antenna is that different types of balanced line have
different velocity factors. Open wire lines will, of consequence, have to be
longer than ladder line which has to be longer than twinlead lines, etc.
See p12.70 of the RSGB Radio Communication Handbook, 6th Ed.
In actual practice, if you transition to coax for the final run into the
shack instead of carrying on with a balanced line (of some appropriate
characteristic impedance), there is going to be very significant radiation
from the coax line, at most frequencies of operation, which can make tuning
difficult and can cause significant TVI and Telephone interference. SWR
values of 5:1 are not unusual on the 80 M band (see p 3-15, HF Antenna Book,
by Bill Orr). Of course, this problem occurs with dipoles as well, but many
people think they won't have that problem because they use a tuner. They
think that because they have tuned the antenna system for a good match in
the shack at the point where it connects to the transmitter, that the line
is flat. This fallacy is easily exposed by putting another of those fancy
twin needle power meters on the antenna side of the tuner and watching what
happens (or doesn't happen) as you transform the impedance of the line to
the 50 ohms needed by the amplifier.
73 de W9DMK
Dan Richardson
Hi Cecil,
Sorry for the prediction Hi.
Even using coax I don't feel a 4:1 SWR on 80 meters is any problem in
terms of additional losses due to SWR. I also don't mind at all using
an antenna tuner. I use mine all the time. It gives me the freedom to
move around on any band with just about any antenna I wish.
73,
Danny
Cecil Moore
Robert Lay wrote:
> There is much quibbling over the length of the 30 to 34 foot matching
> section of the G5RV. It was originally intended to be a multiple of a 1/4
> wavelength at 14 MHz.
Hi Robert, just a minor nit-pick. Since the 3/2WL top section is resonant
on 20m, the "matching section" should be 1/2WL. I know, I know, 1/2WL is
a multiple of a 1/4WL but an odd multiple of 1/4WL won't work worth a darn.
73, Cecil, W6RCA, OOTC
Tom Rauch
>Hi Robert, just a minor nit-pick. Since the 3/2WL top section is resonant
>on 20m, the "matching section" should be 1/2WL. I know, I know, 1/2WL is
>a multiple of a 1/4WL but an odd multiple of 1/4WL won't work worth a darn.
>
>73, Cecil, W6RCA, OOTC
As a point of interest, after using ladder line from my G5RV down to
the tuner, I went back to the regular feed but lengthened the line
slightly to move the 40 meter SWR dip into 40. Now the low end of 80
is fine (2.5:1) , the 40 meter band great (under 1.5:1) , and it's OK
on 20 (3:1) .
Since I mainly work 40, I'm happy.
I can once again dispense with my outdoor tuner and quit frying
crickets.
I was wondering if Chip could run his Genetic Al Gore Rhythm and get
an optimized G5RV.
73 Tom
Tom Rauch
On Wed, 20 Aug 1997 13:02:38 -0700, Cecil Moore
<cecil_...@ccm.ch.intel.com> wrote:
>the information for optimizing the G5RV for any single
>band, including 30m, is on my web page at:
>http://www.geocities.com/CapeCanaveral/8476
>Simply size the "matching section" to feed the twinlead at a
>current maximum point.
Hi Cecil,
What I was think of is a optimum antenna length, feedline Z and
feedline length to produce the best overall compromise on three or
more popular bands WITHOUT any traps or feedpoint/ stub switching.
The G5RV is VERY close, but I'd bet it could be tweeked in a bit
better.
I'm about out of vacuum relays. :-(
73 Tom
Walter Fairclough
I used a commercial G5RV for years but switched to an 'Zepp". I'm really
not happy with the Zepp especially on 20M. Thinking about going back to the
G5RV (102 ft). My G5RV has an impedance matching device at the end of the
ladder line ( I hesitate to call it a balun) to match the length of coax. I
use an antenna tuner (as recommended by the manufacturer).
Having read Cecil's article, am I correct in understanding that his
recommendation is that a standard dipole, center fed with ladder line, is a
better all band antenna than the G5RV?
Here's my dilemma. While the Zepp does pretty good on 80M and 40M, it
leaves a lot to be desired on 20M, 15M and 10M. I am contemplating either
leaving the Zepp up for the 80M and 40M bands or replacing it with the G5RV
and possibly going with a vertical for 20, 15 and 10.
I would appreciate any thoughts.
73
Walter - VE3EN
Cecil Moore
Walter Fairclough wrote:
> Having read Cecil's article, am I correct in understanding that his
> recommendation is that a standard dipole, center fed with ladder line, is a
> better all band antenna than the G5RV?
Hi Walter, in the comparison, I've ignored radiation patterns. The G5RV is
NOT an all-HF-band antenna. For instance, the SWR on the coax on 30m is too
high to be very useful. It requires an antenna tuner on 80m. The dipole that
I have suggested is an all-HF-band antenna and is, on the average, more
efficient and easier to match than the G5RV. It has approximately the same
major lobe radiation patterns but minor lobes are quite different. And it
must be fed with 400-600 ohm parallel-type transmission line to achieve the
low SWRs necessary to eliminate the tuner. Feeding it with 300 ohm line will
result in 50 ohm SWRs greater than 2:1 on some bands.
73, Cecil, W6RCA, OOTC http://people.delphi.com/CecilMoore