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
--
Owen,
That's an excellent job!
You're obviously a good man. Eliminate the pomposity and you'd be a
veritable saint.

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 -

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

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