On Wed, 08 Jun 2005 12:23:50 -0700, Wes Stewart
wrote:

On Wed, 08 Jun 2005 12:52:01 -0400, Buck wrote:

Pardon me while I learn from this discussion.

Hold on Buck.

So far there has been very little "learning" to be done from this
discussion.

I dislike getting personal but I strongly suggest that you reject
anything Fred has put forth. Some of what he says is correct, but for
the most part you are being led astray. Since you don't yet have the
skills to separate the good from the BS, the safest thing to do is
ignore it all.

For example he has suggested that an all-band antenna can be nothing
more than a 130' dipole fed through 100' of 450 ohm line to which you
connect a 50 ohm coax and "your rig will be happy."

Let's examine this premise, shall we.

If you don't already have it, download the free version of EZNEC.

www.eznec.com

If you have MS Excel do the following. If you don't skip down below
the dotted line.


I haven't been ignoring this thread, I have been trying to figure out
eznec. I have managed to make it display a dipole and a two element
beam. I'll need to learn the more advanced features.

I'll try what you say If I can understand the program well enough to
do so.


--
73 for now
Buck
N4PGW

On Wed, 08 Jun 2005 14:16:06 -0700, Wes Stewart
wrote:

On Wed, 08 Jun 2005 12:23:50 -0700, Wes Stewart
wrote:
[snip}

Under "Qualifier" scroll the dropdown menu to either "Generic 450 ohm
window" or if you more more realistic numbers you can select one of
the Wireman Ladder line types. (Ignore "wet" ones.)

This should of course read, "...if you want more realistic..."



I am not sure what I just did or saw. I had several colored graphs
charted and one gray. The gray didn't seem to move around, but the
colored ones sure did. I am afraid I didn't see what you were trying
to show me. I believe the colors were the different feed lines,
capacitors, etc used in the feedline shown. I tried removing them and
only leaving the feedline I chose to use. I don't know if I did
something wrong or not, but the gray line appeared to be the antenna
and it never appeared to move. The feedline markers moved radically.



I haven't thought a lot about the losses in ladder-type feedline, but
I do understand how the losses in coax can reduce High SWR by reducing
both the outgoing and incoming reflected signals in the coax. This
may make the antenna desirable to the rig, but it doesn't do any good
for the operator who is trying to reach or copy that weak signal. It
may well be that the Twin-lead has the same effect. I often read that
one of the advantages of the twin-lead is that it can handle higher
SWR without the higher losses of coax.

I seem to have been seeing a lot about the technology of the twin-lead
tuning technology, but then I can't be sure it wasn't from the same
people here on this forum. I'll continue to look into it to see what
I might learn.

I was able to get past whatever block I had on learning to use EZNEC,
so at least some good came from this discussion. Hopefully, I'll
learn more and can model this antenna and others I read about.

Thanks very much for taking the time to address this with me.

73,
Buck
N4PGW



--
73 for now
Buck
N4PGW

On Thu, 09 Jun 2005 06:23:44 -0500, Cecil Moore
wrote:

Buck wrote:
The G5RV is a twenty meter antenna, isn't it? It needs a tuner on all
other bands if I am not mistaken.

The G5RV needs a tuner on all bands. Acceptable SWRs are
very rare without a tuner. The G5RV is 1.5WL long on
20m. The resonant feedpoint impedance on 20m is in excess
of 100 ohms giving a 50 ohm SWR in excess of 2:1 so a
tuner is required, even on 20m. However, I have done to
a G5RV what Fred has done to a 1/2WL 80m dipole. The
matching section on my G5RV is a variable length between
22' and 38'. My G5RV has an SWR below 1.5:1 on all eight
HF bands. I'm going to write it up one of these days.

This is interesting. I remember reading where the G5RV originated as
a gain dipole for 20 meters. I hadn't looked at it as a 1.5wl dipole.
I have always used 1.5wl dipoles for 15 (40 meters) and had low SWR on
the 15 meter band without a matching network. Am i missing something
or is the coax stealing enough power to reduce the SWR?


--
73 for now
Buck
N4PGW

On Thu, 09 Jun 2005 08:52:39 -0700, Wes Stewart
wrote:

I showed you in detail how to answer your own questions. Did you not
read my post?


I read it and did it. It just took time for me to do so. I posted a
reply to it today.


Thanks


--
73 for now
Buck
N4PGW

On Thu, 9 Jun 2005 00:27:26 -0400, "Fred W4JLE"
wrote:

No buck, the line is always longer than 1/2 wave. It is a matching section
from what is at the antenna to 50 ohms, and then 1/2 wave from that point.

"Buck" wrote in message
.. .
Pardon me while I learn from this discussion.

The 450 ohm antenna is designed to be tuned by using exactly 1/2
electrical wave lengths to match both the transmitter and antenna.
This should mean that any differing feedline should work equally as
well (except for the losses) if I am correct....
SNIP


On Wed, 08 Jun 2005 20:41:58 -0500, Cecil Moore
wrote:

Buck wrote:
Pardon me while I learn from this discussion.

The 450 ohm antenna is designed to be tuned by using exactly 1/2
electrical wave lengths to match both the transmitter and antenna.
This should mean that any differing feedline should work equally as
well (except for the losses) if I am correct....

What you are missing is that first piece of matching section
which can be any length less than 1/2WL. After that first
piece of matching section, you could indeed switch to a
different characteristic impedance. Congratulations, you
have just invented the G5RV. :-)


Fred, I believe that you and Cecil are 180 degrees out of phase. Did
someone make a type-O?

--
73 for now
Buck
N4PGW

Buck wrote:
I seem to have been seeing a lot about the technology of the twin-lead
tuning technology, but then I can't be sure it wasn't from the same
people here on this forum. I'll continue to look into it to see what
I might learn.

The "twin-lead tuning technology" is based on the laws of
physics, not the approval of the gurus on this newsgroup.
--
73, Cecil http://www.qsl.net/w5dxp


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On Thu, 09 Jun 2005 11:38:22 -0500, Cecil Moore
wrote:

Buck wrote:
I am a little confused, so bare with me.....

I put up an antenna with 50 ohm of impedance. I feed it with any
length of 300 ohm feed less than 1/2 L. Then I run 1/2 L of 50 ohm
feed to the radio and I have the 50 ohm match?

Nope, 50 ohms is only one of an infinite number of impedances
you might encounter. For 50 ohms, you feed it with 1/2WL of
300 ohm feedline. This is similar to (but not exactly like)
a G5RV used on 20m.

I put up a 300 ohm antenna. I feed it with 300 ohm twin lead for less
than 1/2 L and 1/2 L of 50 ohm feedline. Is this a 50 ohm match?

Nope, you cannot transform the impedance of a 300 ohm antenna
using 300 ohm feedline. You need reflections to cause an
impedance transformation. A 300 ohm antenna impedance is
not within the green doughnut area below.

The range of impedances that can be matched with a length of
450 ohm ladder-line are represented by the green doughnut at:

http://www.qsl.net/w5dxp/smith.htm

The impedances outside the green area cannot be matched by
only one 450 ohm matching section. The area in the doughnut
hole cannot be matched by only one 450 ohm matching section.


I tried it again and got the picture. It appears that the 450 ohm
twin lead sections can match any impedance between 20 and 100 ohms
given the proper length.


--
73 for now
Buck
N4PGW

Buck wrote:
This is interesting. I remember reading where the G5RV originated as
a gain dipole for 20 meters. I hadn't looked at it as a 1.5wl dipole.
I have always used 1.5wl dipoles for 15 (40 meters) and had low SWR on
the 15 meter band without a matching network. Am i missing something
or is the coax stealing enough power to reduce the SWR?

Bingo! Your 15m SWR at the 40m dipole feedpoint is probably
above 2:1. Feedline losses both ways probably reduce it to
a value tolerated by your transmitter. If you replace the
coax with an integer multiple of 15m halfwavelengths of
ladder-line to reduce losses, your transmitter may object.

I have inadvertently stepped upon an unpublished article with
my posting. I apologize and will bow out.
--
73, Cecil http://www.qsl.net/w5dxp


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On Thu, 9 Jun 2005 16:30:18 -0400, "Fred W4JLE"
wrote:

Given an antenna that has 50 Ohms +J0, feed it with 50 ohm line and the swr
for the system is 1:1, substitute a 1/2 wave of 450 ohm line and the antenna
and the rig are both at 50 ohms. The SWR on the feedline is 450/50 or 9:1.


Ok, just to reiterate so I know I understand (and you can see if I
don't), If I feed a 20 meter dipole cut for my favorite frequency, I
can feed the radio with exactly 1/2 wave of 450 ohm feedline and it
will match the radio? Of course, coax will make a better match (with
less loss?)

Now, if I understand, the principle of the 130 foot dipole matching
the rig is based on the length of 450 ohm twin-lead. The twin lead is
always 1/2 WL long. The coax and rig are 50 ohms, but according to
the smith chart, the impedance of the various frequencies range from
20 to 100 ohms. This would make me wonder why I don't get the same
impedances at my rig, or at least at my feed point of 50 ohm coax.

Thanks


--
73 for now
Buck
N4PGW

Buck wrote:

W5DXP wrote:
What you are missing is that first piece of matching section
which can be any length less than 1/2WL. After that first
piece of matching section, you could indeed switch to a
different characteristic impedance. Congratulations, you
have just invented the G5RV. :-)

Fred, I believe that you and Cecil are 180 degrees out of phase. Did
someone make a type-O?

Well, I made an English language blunder as I was editing my posting.
I should have dropped the which above. The first piece of matching
section, which can be any length less than 1/2WL, brings the impedance
looking into it to a purely resistive value, i.e. a resonant value,
i.e. a current maximum point. So the first section of matching is the
most important. After that, any Z0 could be used, but *only on that
particular band*. That last *constraint* may be what you are missing
(if you are missing anything at all). I am not aware of any phase
difference between Fred and me.
--
73, Cecil http://www.qsl.net/w5dxp


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