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.

Everyone must start somewhere, Owen. 8^)


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.

I suspect it was probably beyond the ability of the Novices back in the
Good Old Days too. In reading the article, I think that is very true.


(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.

Figure 2. (system losses) was a real eye opener! I enjoyed the article
very much.

- 73 de Mike KB3EIA -

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 -

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.

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
--



# measure the VSWR at different frequencies in the 20m band, initially
VSWR should be quite high, and higher at the high end of the band;
# shorten the line a little at a time and repeat from 5 until the VSWR minimum (should be close to 1) occurs at 14.15MHz.

A nice article indeed. The above quote is from the set-up section. My
take is that this empirical approach requires almost no knowledge of
velocity factor at all. In fact, the article recommends against using
vf values listed or tabled in catalogs from suppliers. The reader is
instructed to find the vf ostensibly by experiment. This empirical
approach is the "old school" ham approach that I grew up with: cut and
tweak until you get what you want.

This is where we still live.

Owen, thanks for listing your article. Electrical length is indeed
important. Finding it by experiment is the process. I guess what I'm
trying to say is that, if you can't rely on published vf data and you
have to determine it empirically, you might be able to design a
perfectly good antenna, barely considering vf at all...just measure and
cut and measure and cut and...

John
AB8O

On Sun, 01 Oct 2006 20:25:08 -0400, Mike Coslo
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.

Everyone must start somewhere, Owen. 8^)


Yes of course... but it is demoralising to recommend a procedure to
people when it is not within the capability. They won't be happy
sitting amidst a pile of chopped up ladder line and no result!

....
Figure 2. (system losses) was a real eye opener! I enjoyed the article
very much.

As a cross check, the G5RV's performance is easiest understood on
14MHz (where it is 3 half waves centre fed with a near 1:1 transformer
to the coax) and 28MHz (where it is 6 half waves centre fed with a
near 1:1 transformer to the coax).

Doing a back of the envelope calc for 14MHz where it is fed at a
current maximum indicates ~90 ohm load on the coax, and VSWR ~2:1, so
on the face of it, losses should be relatively low.

Doing a back of the envelope calc for 28MHz where it is fed at a
voltage maximum indicates ~2100 ohm load on the coax, and load end
VSWR ~42:1, so on the face of it, coax losses become much higher. Loss
in 15m of RG58C/U under those conditions is ~8dB, or about 15%
efficiency (coax alone). That reconciles with the graphs... the data
is believable! (You could raise the coax efficiency with RG8X (as
often recommended / supplied) to ~20% , but it still isn't pretty.)

Thanks Mike.

Owen
--

Uhhh guys, I hate to point this out to such an august group, but feel
compelled...

The G5RV is well liked by the appliance operators because it works for
them!!! (doh)


All right now, once you have quit swearing at the monitor screen and
settled your ruffled feathers, ask me why it works... (Walt, please
don't analyze the G5RV again, it has to cause pain and nausea when
doing that.)

Simple, it works because it is unbalanced - and both the unbalanced top
hat and the OCF feed line radiate... Bingo, instant communications,
high angle and low angle... Does it work well?

Well, in a word, NO; not compared to efficient antennas... But the
guys using it don't care (comprehend) that an efficient antenna (more
time and effort) will give a 3dB or even 6dB better signal...

The other thing is the name has cachet... As in, " . . . the antenna
here is a G5RV, that's George Five Radio VICTORY." Just as my
generation took pride in, " the antenna here is an 8JK." (I am a
cognoscenti and your antenna is dirt)

Now, back to our regularily scheduled program analyzing how many angels
can operate CW on the head of a pin...

denny / k8do (busily trying to extract tongue from cheek)

Denny wrote:
Simple, it works because it is unbalanced - and both the unbalanced top
hat and the OCF feed line radiate...

Someone will repeat this and a new myth will be born. :-)
--
73, Cecil http://www.w5dxp.com

On Mon, 02 Oct 2006 13:20:38 GMT, Cecil Moore wrote:

Denny wrote:
Simple, it works because it is unbalanced - and both the unbalanced top
hat and the OCF feed line radiate...

Someone will repeat this and a new myth will be born. :-)

With all due respect, Denny, where did you get your description of the G5RV--in
Mad Magazine? Pardon me if I squash the new myth you just propagated.

The G5RV that I know of is not unbalanced, it has no top hat, it has no OCF feed
line, and if there is a balun between the open-wire and the coax the feed line
will not radiate. Seems like you've confused the G5RV with the psuedo-Windom,
eh?

Walt, W2DU

Walter Maxwell wrote:
With all due respect, Denny, where did you get your description of the G5RV--in
Mad Magazine? Pardon me if I squash the new myth you just propagated.

Walt, did you happen to miss Denny's signature line?

denny / k8do (busily trying to extract tongue from cheek)
--
73, Cecil http://www.w5dxp.com

On Mon, 02 Oct 2006 17:07:04 GMT, Cecil Moore wrote:

Walter Maxwell wrote:
With all due respect, Denny, where did you get your description of the G5RV--in
Mad Magazine? Pardon me if I squash the new myth you just propagated.

Walt, did you happen to miss Denny's signature line?

denny / k8do (busily trying to extract tongue from cheek)

Yes, Cecil, I saw Denny's signature line, but I wasn't sure just how far his
tongue protracted his cheek. Sometimes tongues get stuck that way, just like
kids who get cross-eyed while misbehaving.

Walt

On Mon, 02 Oct 2006 15:43:18 -0400, Walter Maxwell wrote:

On Mon, 02 Oct 2006 17:07:04 GMT, Cecil Moore wrote:

Walter Maxwell wrote:
With all due respect, Denny, where did you get your description of the G5RV--in
Mad Magazine? Pardon me if I squash the new myth you just propagated.

Walt, did you happen to miss Denny's signature line?

denny / k8do (busily trying to extract tongue from cheek)

Yes, Cecil, I saw Denny's signature line, but I wasn't sure just how far his
tongue protracted his cheek. Sometimes tongues get stuck that way, just like
kids who get cross-eyed while misbehaving.

Walt

Denny, as I just now looked SSE from my southern window I discovered a
near-field radiation from a OCF dipole, IDing with K8DO call sign. On looking up
that call I learned why that signal is in the near-fleld zone--it's only 26
miles away in the direction of light travel from my window. If K8DO was using a
balanced G5RV the signal would have evaporated before reaching Mt. Pleasant.
Ever hear of that town? Open yer NW window and yell, I'll hear 'ya.

Walt, W2DU