These are actual measured values for the resonant lengths
of the series section transformer for all HF bands for
my optimized G5RV.

102' dipole, insulated wire. Ladder-line is approximately
Z0=380 ohms, VF = 0.9. Coax is RG-213

The insulation on the wire makes it electrically about 3%
longer, i.e. approximately the same as a 105' uninsulated
dipole. The ladder-line is Wireman #554, #14ga, "440 ohms",
but measures closer to 380 ohms.

Freq-MHz ladder-line length
3.8 23 ft.
7.2 35 ft.
10.125 20 ft.
14.2 29 ft.
18.14 36 ft.
21.3 27 ft.
24.95 29 ft.
28.4 38 ft.

Since my favorite bands are 40m and 17m, I keep the length
of the ladder-line at 36 feet most of the time. I rarely
work 30m so my minimum length is 23 feet. I have lengths
of ladder-line with banana plugs on one end and banana
sockets on the other end. I have one 8 ft. length, one
4 ft. length, one 2 ft. length, and one 1 ft. length so
I can achieve any length between 23 feet and 38 feet to
the nearest one foot. Of course, switches or relays could
be used instead of banana plugs.
--
73, Cecil, http://www.qsl.net/w5dxp



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Cec,

Behaviour of your feedline lengths for the various bands is interesting. But
it's likely optimum lengths for individual bands for anyone else will belong
to a different set. Your list is a guide just to the sort of thing to
expect.

Zo of the feedline has just as much influence on its impedance
transformation properties as does its length. Your measured Zo of 380 ohms
will have an effect considerably different from the nominal ladderline value
of 450 ohms or other impedances which other people may have.

There are, of course, other reasons for variability in optimum feedline
lengths. I don't think G5RV ever specified the impedance of his balanced
line - only that it should be 1/2-wavelength long around 14.15 MHz. Even
50-ohm coax would be OK on the 20m band. It's a fair match at either end.
----
Reg, G4FGQ





"Cecil Moore" wrote in message
...
These are actual measured values for the resonant lengths
of the series section transformer for all HF bands for
my optimized G5RV.

102' dipole, insulated wire. Ladder-line is approximately
Z0=380 ohms, VF = 0.9. Coax is RG-213

The insulation on the wire makes it electrically about 3%
longer, i.e. approximately the same as a 105' uninsulated
dipole. The ladder-line is Wireman #554, #14ga, "440 ohms",
but measures closer to 380 ohms.

Freq-MHz ladder-line length
3.8 23 ft.
7.2 35 ft.
10.125 20 ft.
14.2 29 ft.
18.14 36 ft.
21.3 27 ft.
24.95 29 ft.
28.4 38 ft.

Since my favorite bands are 40m and 17m, I keep the length
of the ladder-line at 36 feet most of the time. I rarely
work 30m so my minimum length is 23 feet. I have lengths
of ladder-line with banana plugs on one end and banana
sockets on the other end. I have one 8 ft. length, one
4 ft. length, one 2 ft. length, and one 1 ft. length so
I can achieve any length between 23 feet and 38 feet to
the nearest one foot. Of course, switches or relays could
be used instead of banana plugs.
--
73, Cecil, http://www.qsl.net/w5dxp



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Reg Edwards wrote:
Behaviour of your feedline lengths for the various bands is interesting. But
it's likely optimum lengths for individual bands for anyone else will belong
to a different set. Your list is a guide just to the sort of thing to
expect.

Yep, my point was that anyone with an MFJ-259B, like mine, can optimize
their own G5RV for true all-HF-band operation especially if they have
a built in autotuner like my IC-756PRO. One complaint I hear is that
the built in autotuners won't tune a G5RV on all HF bands. Well, here's
one way to solve that problem.
--
73, Cecil, W5DXP



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On Wed, 07 Apr 2004 09:50:33 -0500, Cecil Moore
wrote:

Reg Edwards wrote:
Behaviour of your feedline lengths for the various bands is interesting. But
it's likely optimum lengths for individual bands for anyone else will belong
to a different set. Your list is a guide just to the sort of thing to
expect.

Yep, my point was that anyone with an MFJ-259B, like mine, can optimize
their own G5RV for true all-HF-band operation especially if they have
a built in autotuner like my IC-756PRO. One complaint I hear is that
the built in autotuners won't tune a G5RV on all HF bands. Well, here's
one way to solve that problem.

I'm guessing you have no coax here? Just ladderline from antenna to
rig?

Bob
k5qwg

Robert A. Miller wrote:

wrote:
Yep, my point was that anyone with an MFJ-259B, like mine, can optimize
their own G5RV for true all-HF-band operation especially if they have
a built in autotuner like my IC-756PRO. One complaint I hear is that
the built in autotuners won't tune a G5RV on all HF bands. Well, here's
one way to solve that problem.

I'm guessing you have no coax here? Just ladderline from antenna to
rig?

No, no, no! In every respect, my antenna is a G5RV using RG-213 from
the ladder-line series section transformer to the hamshack. If someone
has a G5RV, he can modify it to work virtually perfectly on all HF
bands, including the coax feed. Everything about the G5RV remains the
same except the ladder-line length is modified, and in the case of
75m, a parallel cap is installed. These modifications are super easy.

As an example of virtual perfection on 3.8 MHz, the ladder-line is made
25 feet long and a 1000 pf parallel cap is installed at the ladder-line
to coax junction. The impedance at that junction is very close to 50
ohms resistive so coax is acceptable. Exactly the same techniques can
be applied to all the other HF bands, most of which require no parallel
impedance of any kind.

I will publish the details for each band as I work them out. But this
antenna of mine is a G5RV in all respects. It is a 102 ft dipole fed
with 20-36 feet of ladder-line. The SWR on 3.8 MHz is high so the 1000 pf
capacitor is needed to rotate to 50 ohms through the 1/50 conductance circle.

For the uninitiated, if you have a 25+j25 impedance, you can cause that
impedance to twist to 50+j0 ohms by installing a parallel capacitor. On
75m, that capacitance value is about 700 pf. My antenna works best with
a parallel 1000 pf capacitance on 3.8 MHz.

All G5RVs can be modified to work perfectly on all HF bands. The G5RV
has gotten a bad rap because no one has published those modifications.
But it is actually an excellent all-HF-band antenna. It takes me about
two minutes to change bands from 75m to 40/17m. And, for the lazy, that
change could easily be automated.
--
73, Cecil, W5DXP




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Cecil Moore wrote:
Robert A. Miller wrote:

wrote:

Yep, my point was that anyone with an MFJ-259B, like mine, can optimize
their own G5RV for true all-HF-band operation especially if they have
a built in autotuner like my IC-756PRO. One complaint I hear is that
the built in autotuners won't tune a G5RV on all HF bands. Well, here's
one way to solve that problem.


I'm guessing you have no coax here? Just ladderline from antenna to
rig?


No, no, no! In every respect, my antenna is a G5RV using RG-213 from
the ladder-line series section transformer to the hamshack. If someone
has a G5RV, he can modify it to work virtually perfectly on all HF
bands, including the coax feed. Everything about the G5RV remains the
same except the ladder-line length is modified, and in the case of
75m, a parallel cap is installed. These modifications are super easy.

As an example of virtual perfection on 3.8 MHz, the ladder-line is made
25 feet long and a 1000 pf parallel cap is installed at the ladder-line
to coax junction. The impedance at that junction is very close to 50
ohms resistive so coax is acceptable. Exactly the same techniques can
be applied to all the other HF bands, most of which require no parallel
impedance of any kind.

I will publish the details for each band as I work them out. But this
antenna of mine is a G5RV in all respects. It is a 102 ft dipole fed
with 20-36 feet of ladder-line. The SWR on 3.8 MHz is high so the 1000 pf
capacitor is needed to rotate to 50 ohms through the 1/50 conductance
circle.

For the uninitiated, if you have a 25+j25 impedance, you can cause that
impedance to twist to 50+j0 ohms by installing a parallel capacitor. On
75m, that capacitance value is about 700 pf. My antenna works best with
a parallel 1000 pf capacitance on 3.8 MHz.

All G5RVs can be modified to work perfectly on all HF bands. The G5RV
has gotten a bad rap because no one has published those modifications.
But it is actually an excellent all-HF-band antenna. It takes me about
two minutes to change bands from 75m to 40/17m. And, for the lazy, that
change could easily be automated.


As a G5RV is to a dipole, is your modification *really* a G5RV? Seems
to me that you have a ladder line and capacitor tuned dipole, not a G5RV.

Does the 102 foot dipole have to be called a G5RV? Heck, Cecil - you
might just be able to call this the W5DXP antenna. Seems different
enough to me! 8^)

And perhaps your modifications actually show a little bit of why the
G5RV gets a bad rap! 8^)

In the interim, I'm watching this with great interest. It might just
be a great solution for me. I can get 102 feet of wire up. I have 96
feet with a tuner now.

Do You switch the capacitance in and out, or use variables? And if you
switch, do you have the caps at the coax ladderline junction or in the
shack?

Possible really stupid question alert!: When you speak of the ladder
line being 20-36 feet, and or 25 feet for 3.8 mHz (with cap) you mean
that the total height from the coax/ladder line junction to the antenna
itself must be the length of the shortest piece of tuning ladder line?

IOW, If I run my coax to the roof of my house to the box I would
construct to hold the different lengths of tuning line and switching
electronics, I could only have the antenna roughly 25 feet above this
box? If so, I can still probably get the antenna 50 feet above the ground.

Any problems with rolling the ladder line?



- Mike KB3EIA -

Mike Coslo wrote:
As a G5RV is to a dipole, is your modification *really* a G5RV?
Seems to me that you have a ladder line and capacitor tuned dipole, not
a G5RV.

The cap is only on 75m to lower the 50 ohm SWR. It doesn't have to be
installed if one can tolerate a 3:1 SWR.

Does the 102 foot dipole have to be called a G5RV? Heck, Cecil - you
might just be able to call this the W5DXP antenna. Seems different
enough to me! 8^)

The physical difference is negligible. It is still a 102 ft dipole fed
with a series section transformer made out of ladder-line and fed with
coax from that point to the shack.

Do You switch the capacitance in and out, or use variables? And if
you switch, do you have the caps at the coax ladderline junction or in
the shack?

As I said earlier, if you can tolerate a 3:1 SWR, you don't need the cap.
Presently I switch the cap in and out by hand. My G5RV is at 40 ft. on
the ends and I just grab the feedline and pull it down to access the
ladder-line/coax junction where the cap is installed for 75m - thus
eliminating the need for a tuner. It only takes a minute or two to pull
on the feedline and plug or unplug the cap. I hope that's clear. Here's
a diagram for 75m operation:

XMTR---any length 50 ohm coax---+cap+---25 ft. 450 ohm feedline---102' dipole

The parallel 1000 pf cap is across the two feedlines at the twinlead/coax
junction.

Possible really stupid question alert!: When you speak of the ladder
line being 20-36 feet, and or 25 feet for 3.8 mHz (with cap) you mean
that the total height from the coax/ladder line junction to the antenna
itself must be the length of the shortest piece of tuning ladder line?

Maybe a confusing question? I have 8, 4, 2, 1 ft pieces of ladder-line
that I insert between the 21 ft. minimum length of ladder-line and the coax.
That allows me to vary the length of the series section transformer from 21
ft minimum to 36 feet maximum. Obviously, I could use one more length to
increase it by X amount.

IOW, If I run my coax to the roof of my house to the box I would
construct to hold the different lengths of tuning line and switching
electronics, I could only have the antenna roughly 25 feet above this
box? If so, I can still probably get the antenna 50 feet above the ground.

I had envisioned mounting the box on a 2x4 sticking straight up at the
middle of the dipole. But I could probably mount the box on my roof.

Any problems with rolling the ladder line?

DON'T ROLL THE LADDER-LINE! Keep adjacent loops at least six inches apart.
Here's an idea that I have been toying with. It involves varying the length
of the coax as well as the length of the ladder-line to maintain a constant
total length of feedline. This is a physical solution to the mechanical
problem and has virtually no electrical effect.

XMTR-----coax------------ ----coax---- ------coax------
A B C
==twinlead== ====twinlead==== ==twinlead==dipole

This is for illustration only. Not all the switchable lengths of twinlead
are shown. Only two are shown.

We need a DPDT relay at A and C. We need a 4PST relay at B and other points
like B. For minimum twinlead, we could have a coax to coax connection at
points A and B and a coax to twinlead connection at point C. For maximum
twinlead, we would have a coax to twinlead connection at A and a twinlead
to twinlead connection at points B and C. The physically parallel coax
and twin lead would have to be physically separated, maybe one on each side
of a 2x4 about a foot apart.

An SWR sensing circuit could be added to turn this thing into an autotuner
for a G5RV. Hope I didn't get carried away. These are just some random
thoughts toward perfection of the G5RV.
--
73, Cecil, W5DXP



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Cecil Moore wrote:

An SWR sensing circuit could be added to turn this thing into an autotuner
for a G5RV. Hope I didn't get carried away. These are just some random
thoughts toward perfection of the G5RV.

Not at all, Cecil! I've printed this out and am looking at it now.
Thanks, much!

- Mike KB3EIA -