Open wire feedlines
 

I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug

Doug wrote:
I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug


Hi Doug,

Is your antenna 135' long and 35' high? I'm not sure if you were
implying that the 35 feet of open wire line was only part of the
transmission line. So, how high is the center of the antenna, and how
high are the ends?

If, in fact, it is a relatively low antenna (under 40' above ground),
then yes, that will present a high impedance to your tuner. But don't
add more transmission line to it. And never coil it up. Either one
will only degrade the antenna's performance.

I don't know what kind of tuner you are using, but a center-fed fullwave
antenna is a challenge to just about any tuner, from this end of the wire.

Try this, just for grins (only for 40 meters): take your end of the
twinlead and gently twist them together and stick them into the center
conductor of the output connector. I assume you have a great, short
ground that you are working against.

That should be something that you can tune, and assuming that your
twinlead doesn't get too close to metal on its way to the tree, you
should do better.

My preference would be that you could load up your original
configuration with the tuner, but you are trying to center-feed a
fullwave dipole (see links below - the last one).

One other option, if you can do this, would be to feed if offset from
the center. The Windom antenna does this successfully, and works great
(not just good; great!) on 80 and 40 both. Links are at the bottom of
this posting.

Hope this helps, and let us know what you do!

73,
Dave
kz1o

Links:
http://tinyurl.com/5arad
http://tinyurl.com/43nbo
http://www.njqrp.org/n2cxantennas/halfer/
http://tinyurl.com/3nyx6

Try this, just for grins (only for 40 meters): take your end of the
twinlead and gently twist them together and stick them into the center
conductor of the output connector. I assume you have a great, short
ground that you are working against.

That should be something that you can tune, and assuming that your
twinlead doesn't get too close to metal on its way to the tree, you
should do better.

That could be a good top-loaded vertical.
make sure you have a good ground, like he said.

I wanted to try that with my G5RV, but never got a chance before moving to a
new qth.
Its on my list of things to do.

I've also heard of folks switching in and out different lengths of feedline.
but the same problem arises - that is - what to do with the extra feedline.



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"Dave Bushong" wrote in message
...
Doug wrote:
I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug


Hi Doug,

Is your antenna 135' long and 35' high? I'm not sure if you were
implying that the 35 feet of open wire line was only part of the
transmission line. So, how high is the center of the antenna, and how
high are the ends?

If, in fact, it is a relatively low antenna (under 40' above ground),
then yes, that will present a high impedance to your tuner. But don't
add more transmission line to it. And never coil it up. Either one
will only degrade the antenna's performance.

I don't know what kind of tuner you are using, but a center-fed fullwave
antenna is a challenge to just about any tuner, from this end of the wire.

Try this, just for grins (only for 40 meters): take your end of the
twinlead and gently twist them together and stick them into the center
conductor of the output connector. I assume you have a great, short
ground that you are working against.

That should be something that you can tune, and assuming that your
twinlead doesn't get too close to metal on its way to the tree, you
should do better.

My preference would be that you could load up your original
configuration with the tuner, but you are trying to center-feed a
fullwave dipole (see links below - the last one).

One other option, if you can do this, would be to feed if offset from
the center. The Windom antenna does this successfully, and works great
(not just good; great!) on 80 and 40 both. Links are at the bottom of
this posting.

Hope this helps, and let us know what you do!

73,
Dave
kz1o


Hi Dave,

Thanks for your info.

The antenna is only 25 ft up with a total transmission line length of 35 ft.

I know that the feed point of any such low antenna will not be 50 ohms,
however,
it will not necesarily be higher than that at the center feedpoint of the
antenna.
The impedance will vary with a lot of factors.

If I understand my antenna theory correctly, a 135 ft dipole is essentially
a full wave
antenna on 40 mtrs with a high impedance feedpoint regardless of ground
height.
At 1/4 wave lengths of feedline (which is approximately what I currently
have)
there will be high impedance nodes. Thus my idea of lengthening the ladder
line to
eliminate the high impedance feedpoint.

However, your idea of tying the ladderline together at the tuner and feeding
the antenna as
an end fed wire against ground (I do have a good short earth ground), is a
good one.

73,

Doug

Doug,

I think what is happening is that the end of feeder impedance is very LOW on
40 M. The center impedance of a full wave dipole is very high, but
transformed over the 1/4 wavelength line you are using as a feeder, it will
present a very low impedance to your tuner. Your losses are due to the high
currents present at a low feed point impedance. Add another 1/8 wave or
about 17 feet of feeder and try it again. The tuning will change on all the
other bands but generally, you can find a feeder length that will work on
all bands.

The other question is what type of tuner are you using and what is its
matching range? QST had an article on tuner efficiency and matching ranges
recently and if yours is one of the ones tested, you will find this article
very interesting. I always recommend the Johnson "Matchbox" as the best
commercially available tuner for open wire line.

73,
Chuck...K1KW

"Doug" wrote in message
...

I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug

Doug,
What to do with the excess
length?
Suspending it in the air would work.

Wind it spirally around the tree that acts as a center support?
It would be worth a try.

Here is some info that you might find useful .
(Taken from webpage http://www.bloomington.in.us/~wh2t/zepp.html )

With this type antenna the feed line should be routed away from the antenna
at a right angle for as great a distance as possible. This will prevent
current imbalance in the feed line caused by RF pickup from the antenna. A
right-angle departure of 1/4 wavelength or greater is suggested.

To avoid problems matching any center fed antenna with high impedance open
wire lines, keep the feedline around these lengths.

[The WORST POSSIBLE line lengths are shown in brackets]

40 meter antenna 42-52, 73-83, 112-123 or 145-155 feet
[Avoid 32, 64, 96, 128 ft]

Some slight trimming or adding of feedline may be necessary to accommodate
the higher frequency bands.

Good Luck, Ace - WH2T





"Doug" wrote in message
...

I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug

This is actually very misleading and in fact UNTRUE!

After careful review of the referenced web site, the suggestions for
feedline lengths to avoid are for a double extended zepp, NOT a centerfed
full wave dipole for 40M, where this original question originated.

My original suggestion stands and I suggest the originator of this thread
try it and report back!

73, Chuck





"Dr.Ace - WH2T" wrote in message
...
Doug,
What to do with the excess
length?
Suspending it in the air would work.

Wind it spirally around the tree that acts as a center support?
It would be worth a try.

Here is some info that you might find useful .
(Taken from webpage http://www.bloomington.in.us/~wh2t/zepp.html )

With this type antenna the feed line should be routed away from the
antenna
at a right angle for as great a distance as possible. This will prevent
current imbalance in the feed line caused by RF pickup from the antenna. A
right-angle departure of 1/4 wavelength or greater is suggested.

To avoid problems matching any center fed antenna with high impedance open
wire lines, keep the feedline around these lengths.

[The WORST POSSIBLE line lengths are shown in brackets]

40 meter antenna 42-52, 73-83, 112-123 or 145-155 feet
[Avoid 32, 64, 96, 128 ft]

Some slight trimming or adding of feedline may be necessary to accommodate
the higher frequency bands.

Good Luck, Ace - WH2T





"Doug" wrote in message
...

I recently put up a 135 ft dipole with open wire (ladder line) feed.

It worls fine on all bands except for 40 mters. I'm only using around
35 feet of open wire line and the result is that the antenna presents
a very high impedance on 40 meters. I'm losing much of the power in
my tuner.

I need to lengthen the feed line but what to do with the excess
length?

Can I simply tie it up into a bundle, suspending it in air?
Wind it spirally around the tree that acts as a center support?
Any other suggestions?

tnx,

Doug