Some months ago I put some thoughts together to assist our newly
minted 6-hour hams who seem attracted to either short end-fed wires
(although they refer to them as long-wires) or G5RVs.

This article deals with optimising a typical G5RV (as distinct from an
optimal G5RV).

I ceased efforts when it became apparent that the procedure was beyond
the base competency level for our Foundation Licence, and therefore
beyond the target audience. (Another issue was that it required
transmitting a test carrier on 20m which is not one of their permitted
bands, so technically they would need assistance.)

Nevertheless, I looked over it today and fixed a few typos.

http://www.vk1od.net/G5RV/optimising.htm

Comments welcome.

Owen
--

Owen Duffy wrote:
Some months ago I put some thoughts together to assist our newly
minted 6-hour hams who seem attracted to either short end-fed wires
(although they refer to them as long-wires) or G5RVs.



I ceased efforts when it became apparent that the procedure was beyond
the base competency level for our Foundation Licence,
Comments welcome.

Owen
--
Man,
Get over yourself!

jawod wrote:
Owen Duffy wrote:
I ceased efforts when it became apparent that the procedure was beyond
the base competency level for our Foundation Licence, Comments welcome.

Man,
Get over yourself!

In Transactional Analysis, we call that a crossed
transaction. :-)
--
73, Cecil http://www.w5dxp.com

On Sun, 01 Oct 2006 01:12:02 -0400, jawod wrote:

Owen Duffy wrote:
Some months ago I put some thoughts together to assist our newly
minted 6-hour hams who seem attracted to either short end-fed wires
(although they refer to them as long-wires) or G5RVs.



I ceased efforts when it became apparent that the procedure was beyond
the base competency level for our Foundation Licence,
Comments welcome.

Owen

Hi Owen--great job! But you said "comments welcome", so please don't be offended
by what I have to say.

I have always been curious about all the hype, excitement, and marketing
popularity of the G5RV, So I included a section on this antenna in both editions
of Reflections, ed 1 in 1990, and ed 2 in 2001, in an attempt to educate the
newcomers to its realities. So I invite you to read the pertinent section from
the book below:

The following is a quote from Chapter 20 in "Reflections-Transmission Lines and
Antennas," authored by W2DU.

"Sec 20.2.4 The G5RV Antenna

With this background on random-length dipoles behind us, it seems
appropriate to make a critical examination of a particular 102-foot dipole that
is enjoying a great deal of popularity--Louis Varney's G5RV dipole. In spite of
its popularity, its operation is not well understood among many amateurs, so
I'll shed a little light on the G5RV. First of all, the reason for the 102-foot
length for the G5RV is no secret, but it is not well known. Being unaware of
certain antenna principles, many amateurs have come to believe that there is
some sort of magic in the 102-foot length, and that their all-band success with
this antenna is dependent on this specific length. Nothing could be further from
the truth, because, except for 20 meters (as I'll soon explain), any random
length of at least 3 lambda/2 long at the lowest operating frequency will
perform equally well.
What is the significance of the 102-foot length? Unbeknown to many amateurs
who use it, Varney designed the antenna to be a resonant 3 lambda/2 radiator on
20 meters--that length is 102 feet. He had two specific reasons for selecting 3
lambda/2 on 20--he wanted a four-lobe radiation pattern and a low feed-point
impedance. The 3 lambda/2 was a clever choice, because this length yields a
four-lobe pattern, in addition to a low feed-point impedance that can be matched
to a 50-ohm line with a line transformer without requiring an antenna tuner. As
Varney also intended, this 102-foot length results in a strictly random length
on all bands except 20, so except for the 20-meter considerations I've just
described, there is no magic whatever to this length. The last comment in the
previous paragraph should be taken seriously. It should be noted that the
102-foot length of the G5RV is almost exactly the length I recommended above for
a random-length antenna, 3 lambda/8 at the lowest frequency of operation,
because 100 feet is the length required for 3 lambda/8 at 3.5 MHz.
On 20 meters, the input impedance of the 3 lambda/2 G5RV radiator is low
because the feed point is at the center of the central 1/2 wl portion. Hence,
the impedance (the resonant resistance) is only moderately higher than if the
outer 1/2 wl sections were eliminated, leaving a single 1/2 wl dipole. At the
frequency of mid-band resonance, the free-space feed-point impedance is
approximately 100 + j0 ohms, which reduces to around 90 + j0 ohms at a
convenient height above ground. This results in a mismatch of about 1.8:1
relative to 50 ohms. Varney's choice of the 34-foot line-transformer matching
section, 1/2 wl on 20 meters, was to make a 1:1 impedance- transformer that
repeats the 90 + j0 antenna impedance at its input terminals. Thus, with a
suitable choke balun to make a transition from a balanced to an unbalanced line,
the low 1.8:1 mismatch makes connecting to a 50-ohm line feasible without
requiring an antenna tuner. The SWR on a 1/2 wl matching section of 300-ohm line
is around 3.3:1, while on a 450-ohm line it is about 5:1. Keep in mind that
these considerations apply only to 20-meter operation. On all other bands, the
G5RV antenna terminal impedance is much higher and reactive, resulting in a
higher SWR and making the use of an antenna tuner imperative. Incidentally, the
length of a 3 lambda/2 radiator may be found using the long-wire antenna formula
length in feet = 492(n - 0.05)/f MHz, (Eq 20-3)

where n = the number of half wavelengths in the radiator

It is unfortunate that many amateurs believe that the balun should be omitted.
These people have been misled, because failure to include a balun between the
balanced open wire and the unbalanced coax results in RF radiation in the shack
from current flow on the outer surface of the coax shield.
In addition to the misunderstanding concerning the "magical" 102-foot
length of the G5RV, there are also other areas of confusion focused on this
antenna, some concerning the role of the feed line. There are some who believe
that a particular combination of open-wire and coaxial feed line yields a
perfect 1:1 match on all bands without a tuner. As stated above, this is true
only on 20 meters. Others believe that because the 102-foot dipole length is
shorter than 1/2 wl on 80 meters, a certain length of the feed line is a
folded-up portion of the antenna to make up for the difference in length, and
that the folded-up portion radiates along with the antenna. Still others believe
certain lengths of feed line are to be avoided to prevent "antenna current" from
flowing on the feed line because of line resonance. Patently untrue! I wish I
knew how these myths originate.
My own involvement with the G5RV antenna dates back to the early '70s when
I began lecturing on SWR and reflections on transmission lines. My lectures
promoted the use of antenna tuners with open-wire feed line on random-length
antennas as the best way to achieve all-band operation. I also promoted the
concept that the correct length of feed line is that which is required to reach
from the antenna terminals to the tuner, because, regardless of the length of
the feed line, both the feed line and the antenna are made resonant by the
conjugate matching action of the tuner. Hence, there is no reason to avoid
certain lengths to prevent line resonance, because the tuner makes them resonant
anyway.
I first heard of the G5RV when someone in my audience described his
102-foot antenna with open-wire and coax feed line. He claimed it gave him a 1:1
SWR on all bands without a tuner. I told him he must have a lossy coax to get
1:1, because I knew a 1:1 would be impossible with such an arrangement without
some exceptionally high resistive loss somewhere in the antenna system. After
hearing several more identical claims in later lecture sessions, I analyzed the
antenna on all bands, observing it to be the 3 lambda/2 that it is on 20 meters,
but a random length on all other bands, so I felt confident in rebutting the
ridiculous "1:1 on all bands without a tuner" claims. Incidentally, Varney
published an update of the G5RV in The ARRL Antenna Compendium, Volume 1 (Ref
112), in which he presented the same specifications for the antenna that I
described above, which confirms my earlier observation that his antenna is 3
lambda/2 on 20 meters, and a random length on all other bands.
Let's now examine the other myths and confusion concerning the G5RV that I
mentioned earlier. First, we'll consider the feed-line combination believed to
yield a 1:1 match on all bands. It has been written that the combination of 33
feet of open-wire line, plus 68 feet of 50-ohm coaxial line will yield such a
match. Don't you believe it! A determination of the G5RV antenna-terminal
impedance on all bands shows that there is no length of open-wire line of any
characteristic impedance Zo that will transform the antenna impedance Za to an
impedance that is even close to presenting a match to 50- or 75-ohm coax, except
on 20 meters. However, when fairly long lengths of coax follow a length of open
wire, the high SWR appearing at the junction of the open wire and the coax will
be reduced significantly at the input of the coax because of the attenuation
loss in the coax, especially at the higher frequencies. The longer the coax, the
lower the input SWR, but remember that this method of lowering the SWR is costly
in terms of lost power. Because an antenna tuner is necessary anyway, except on
20 meters, it makes no sense to use any coax at all. Coax performs no useful
function in the feed system, and it consumes power unnecessarily because of the
high SWR. A more sensible method is to run the open-wire line all the way to the
tuner and eliminate the coax entirely.
Second, let's consider the length of feed line believed to be a folded-up
portion of the antenna that radiates. Radiation occurs when the electromagnetic
field developed by current flow on a conductor is not canceled by an opposing
field developed by an equal current flowing in the opposite direction. Hence,
radiation occurs as a result of current flowing on an antenna. However, antenna
current ceases being antenna current at the antenna terminals, because once it
enters the transmission line, the current becomes transmission-line current,
with the current in the two conductors flowing in opposite directions. There is
no radiation from any portion of the line, because the fields developed by the
currents flowing in opposite directions in the two conductors oppose and cancel
each other throughout the entire length of the line. Therefore, no portion of
the feed line becomes part of the antenna."

Owen, I didn't include this to detract from your excellent work--you've done a
great job. But my position is that since an antenna tuner is necessary anyway
for the antenna to be multibanded, why insert any coax at all?

Walt, W2DU

Walter Maxwell wrote:
There is
no radiation from any portion of the line, because the fields developed by the
currents flowing in opposite directions in the two conductors oppose and cancel
each other throughout the entire length of the line. Therefore, no portion of
the feed line becomes part of the antenna."

Hi Walt, I agree with what you said and here is an addition.
A graphic on my web page shows why the G5RV is decently
matched by coax on 75m and 40m as well as 20m.

http://www.qsl.net/w5dxp/G5RV.HTM

The 1/2WL of 300 ohm series section is what the antenna
needs to repeat the resonant feedpoint impedance on 20m.
I still don't know why Mr. Varney installed the 1/2WL
300 ohm section for 20m operation. Why not 100% coax?

The 1/4WL of 300 ohm series section is close to what
the antenna needs to transform the 40m feedpoint impedance
to a nearly pure low resistive value. This can be seen
on the Smith Chart.

The 1/8WL of 300 ohm series section is close to what
the antenna needs to transform the 75m feedpoint impedance
to a nearly pure low resistive value. This can also be
seen on the Smith Chart.

The 0.88WL of 300 ohm series section is close to what
the antenna needs to transform the 12m feedpoint impedance
to a purely low resistive value. I didn't bother showing
this one because it goes more than once around the Smith
Chart.
--
73, Cecil http://www.w5dxp.com

On Sun, 01 Oct 2006 14:22:40 -0400, Walter Maxwell
wrote:

On Sun, 01 Oct 2006 01:12:02 -0400, jawod wrote:

Hi Owen--great job! But you said "comments welcome", so please don't be offended
by what I have to say.

Walt, the intention was to seek constructive comment. Of course, there
is always the risk of personal comment... but that is part of the cost
of technical review as you know.


I have always been curious about all the hype, excitement, and marketing
popularity of the G5RV, So I included a section on this antenna in both editions
of Reflections, ed 1 in 1990, and ed 2 in 2001, in an attempt to educate the
newcomers to its realities. So I invite you to read the pertinent section from
the book below:

....


The following is a quote from Chapter 20 in "Reflections-Transmission Lines and
Antennas," authored by W2DU.

"Sec 20.2.4 The G5RV Antenna

With this background on random-length dipoles behind us, it seems
appropriate to make a critical examination of a particular 102-foot dipole that
is enjoying a great deal of popularity--Louis Varney's G5RV dipole. In spite of
its popularity, its operation is not well understood among many amateurs, so
I'll shed a little light on the G5RV. First of all, the reason for the 102-foot
length for the G5RV is no secret, but it is not well known. Being unaware of
certain antenna principles, many amateurs have come to believe that there is
some sort of magic in the 102-foot length, and that their all-band success with
this antenna is dependent on this specific length. Nothing could be further from
the truth, because, except for 20 meters (as I'll soon explain), any random
length of at least 3 lambda/2 long at the lowest operating frequency will
perform equally well.

I am not sure if "3 lambda/2 long at the lowest operating frequency"
is what you really meant... perhaps I am misunderstanding it.

Copying a quote from one of my articles, "my experience is that where
a centre fed dipole less than about 0.35 wavelengths in length, it is
difficult to achieve acceptable feed system efficiency in practical
configurations". In fractional terms, I would state that minimum
length as about 3/8 wavelength.

What is the significance of the 102-foot length? Unbeknown to many amateurs

....

I heard this story from an amateur friend (now deceased) who knew
Louis in the old country, and he used chuckle at the newfound role of
the G5RV as an efficient all band antenna (which it isn't).

....

It is unfortunate that many amateurs believe that the balun should be omitted.
These people have been misled, because failure to include a balun between the
balanced open wire and the unbalanced coax results in RF radiation in the shack
from current flow on the outer surface of the coax shield.

Agreed. Unfortunately Varney confused the issue with his later article
that rescinded his advice to use a balun.

I think the words in may latest article "Varney originally described
the G5RV with a balun at the coax to parallel line transition, and
changed his mind in a later article due to uncertainty about the balun
design. More has been learnt of baluns and antennas in the meantime,
and there is no doubt that inclusion of an effective choke balun at
that transition will assist in minimising feedline contribution to
radiation, and conversely, feedline pickup." are valid.


Owen, I didn't include this to detract from your excellent work--you've done a
great job. But my position is that since an antenna tuner is necessary anyway
for the antenna to be multibanded, why insert any coax at all?

Agreed Walt, and no offence taken. Discussion of the issues is what
our hobby is (or was) about.

Our dear departed friend Reg would hop into me when I wrote about
G5RVs suggesting that I sold the things, that my perspective was that
of a salesman and that I was not detached. He was wrong, I have
erected a G5RV for the purpose of experiencing the thing, of learning
about it, but the trade-offs involved in a G5RV haven't suited my
interests for more than that few hours.

The graphs in my two G5RV articles are based on thousands of model
outcomes, starting from NEC models of the radiator in a typical
configuration, and then exact transmission line models and tuner
models.

The thing that I have learned is that most of the loss in typical
configurations is in the coax, the loss in the coax is driven by what
it happening on the radiator and open line section, and that reduction
of coax loss is the key to efficiency. An obvious way to reduce coax
loss is to reduce (even eliminate) the coax (though a systems
perspective shows that you don't just deduct the coax loss, ATU loss
will increase marginally at some frequencies). That is the subtlety in
my words "This article deals with optimising a typical G5RV (as
distinct from an optimal G5RV)" The theme being that if you have a
typical G5RV, here is how to go about getting the best out of what you
have, if you want to improve it, read the other article linked at the
bottom the page.

Owen
--

Owen Duffy wrote:
On Sun, 01 Oct 2006 14:22:40 -0400, Walter Maxwell
wrote:


On Sun, 01 Oct 2006 01:12:02 -0400, jawod wrote:


Hi Owen--great job! But you said "comments welcome", so please don't be offended
by what I have to say.


Walt, the intention was to seek constructive comment. Of course, there
is always the risk of personal comment... but that is part of the cost
of technical review as you know.


I have always been curious about all the hype, excitement, and marketing
popularity of the G5RV, So I included a section on this antenna in both editions
of Reflections, ed 1 in 1990, and ed 2 in 2001, in an attempt to educate the
newcomers to its realities. So I invite you to read the pertinent section from
the book below:


...


The following is a quote from Chapter 20 in "Reflections-Transmission Lines and
Antennas," authored by W2DU.

"Sec 20.2.4 The G5RV Antenna

With this background on random-length dipoles behind us, it seems
appropriate to make a critical examination of a particular 102-foot dipole that
is enjoying a great deal of popularity--Louis Varney's G5RV dipole. In spite of
its popularity, its operation is not well understood among many amateurs, so
I'll shed a little light on the G5RV. First of all, the reason for the 102-foot
length for the G5RV is no secret, but it is not well known. Being unaware of
certain antenna principles, many amateurs have come to believe that there is
some sort of magic in the 102-foot length, and that their all-band success with
this antenna is dependent on this specific length. Nothing could be further from
the truth, because, except for 20 meters (as I'll soon explain), any random
length of at least 3 lambda/2 long at the lowest operating frequency will
perform equally well.


I am not sure if "3 lambda/2 long at the lowest operating frequency"
is what you really meant... perhaps I am misunderstanding it.

Copying a quote from one of my articles, "my experience is that where
a centre fed dipole less than about 0.35 wavelengths in length, it is
difficult to achieve acceptable feed system efficiency in practical
configurations". In fractional terms, I would state that minimum
length as about 3/8 wavelength.


What is the significance of the 102-foot length? Unbeknown to many amateurs


...

I heard this story from an amateur friend (now deceased) who knew
Louis in the old country, and he used chuckle at the newfound role of
the G5RV as an efficient all band antenna (which it isn't).

I think there is a significant proportion of the Ham population that
refers to just about *any* wire antenna as a G5RV. I've heard about half
wave G5RV's, Coax fed, ladder line fed, (as in doublet) lots of
variations! ;^)


It is unfortunate that many amateurs believe that the balun should be omitted.
These people have been misled, because failure to include a balun between the
balanced open wire and the unbalanced coax results in RF radiation in the shack

from current flow on the outer surface of the coax shield.

Agreed. Unfortunately Varney confused the issue with his later article
that rescinded his advice to use a balun.

I think the words in may latest article "Varney originally described
the G5RV with a balun at the coax to parallel line transition, and
changed his mind in a later article due to uncertainty about the balun
design. More has been learnt of baluns and antennas in the meantime,
and there is no doubt that inclusion of an effective choke balun at
that transition will assist in minimising feedline contribution to
radiation, and conversely, feedline pickup." are valid.



Owen, I didn't include this to detract from your excellent work--you've done a
great job. But my position is that since an antenna tuner is necessary anyway
for the antenna to be multibanded, why insert any coax at all?


Agreed Walt, and no offence taken. Discussion of the issues is what
our hobby is (or was) about.

Our dear departed friend Reg would hop into me when I wrote about
G5RVs suggesting that I sold the things, that my perspective was that
of a salesman and that I was not detached. He was wrong, I have
erected a G5RV for the purpose of experiencing the thing, of learning
about it, but the trade-offs involved in a G5RV haven't suited my
interests for more than that few hours.

The graphs in my two G5RV articles are based on thousands of model
outcomes, starting from NEC models of the radiator in a typical
configuration, and then exact transmission line models and tuner
models.

The thing that I have learned is that most of the loss in typical
configurations is in the coax, the loss in the coax is driven by what
it happening on the radiator and open line section, and that reduction
of coax loss is the key to efficiency. An obvious way to reduce coax
loss is to reduce (even eliminate) the coax (though a systems
perspective shows that you don't just deduct the coax loss, ATU loss
will increase marginally at some frequencies). That is the subtlety in
my words "This article deals with optimising a typical G5RV (as
distinct from an optimal G5RV)" The theme being that if you have a
typical G5RV, here is how to go about getting the best out of what you
have, if you want to improve it, read the other article linked at the
bottom the page.

Perhaps getting the best out of it is to lower it to about 4 feet, and
use it as a cattle fence? As noted above, we might as well eliminate the
coax altogether.

- 73 de Mike KB3EIA -

On Sun, 01 Oct 2006 14:22:40 -0400, Walter Maxwell wrote:

any random
length of at least 3 lambda/2 long at the lowest operating frequency will
perform equally well.

There is a typo in the above sentence. "3 lambda/2" should be changed to read "3
lambda/8". Sorry about that, my ploof reader goofed.

Walt, W2DU

Owen Duffy wrote:
http://www.vk1od.net/G5RV/optimising.htm
Comments welcome.

Great job as usual, Owen. I would add a couple of
items.

1. Some commercial antennas, sold as G5RV's, deviate
from your information because they deviate from your
specifications and tuning procedures. They may need
to be tuned to your specifications.

2. The following statement is somewhat confusing.

Fig 1 shows the efficiency of a optimised typical G5RV.
Note that only three of these peaks coincide with an amateur
band, but 40m efficiency is 65% although not at the peak.

The resolution of the graph makes it difficult to know which
three peaks are in which three bands. Like 40m, you might also
state that 15m efficiency is xx% although not at the peak.
--
73, Cecil http://www.w5dxp.com

On Sun, 01 Oct 2006 11:32:09 GMT, Cecil Moore
wrote:

Owen Duffy wrote:
http://www.vk1od.net/G5RV/optimising.htm
Comments welcome.

Great job as usual, Owen. I would add a couple of
items.

1. Some commercial antennas, sold as G5RV's, deviate
from your information because they deviate from your
specifications and tuning procedures. They may need
to be tuned to your specifications.

Not just commercial ones Cecil. For decades I have taken an interest
in the detail of the "other station's" G5RV in QSOs, and they vary
widely.


2. The following statement is somewhat confusing.

Fig 1 shows the efficiency of a optimised typical G5RV.
Note that only three of these peaks coincide with an amateur
band, but 40m efficiency is 65% although not at the peak.

It is not a marvellous bit of prose, is it. I added the bit about 40
as a balance that although there wasn't a peak in 40m, 40m was well up
the curve. I will rethink a clearer way of expressing it.


The resolution of the graph makes it difficult to know which
three peaks are in which three bands. Like 40m, you might also
state that 15m efficiency is xx% although not at the peak.

Yeah, I didn't really want to deal with how good a "typical" G5RV was
or wasn't rather just set the stage for why it was worth fine tuning
in situ. I stated in my posting our newly minted hams like them, and
when you start with a power limit that is 10dB behind the average, you
don't need to throw more power away in the antenna system.

Owen
--