coax end fed wire
 

Hello, I am looking to put up my first HF antenna. I have considered a
trap dipople in the attic, but seeing this is a one story house and
only 25 feet long it would only be about 15 feet off the ground and
more trap than radiator. I have also considered a mass produced
verticle to go on the existing tripod on the roof, but as I am
currently on medical leave it is not in the budget. My plan is to run
an approximately 80 foot wire from the existing tripod on top of the
house length wise accross the backyard to either a pole erected at the
fence line, or a tree on the other side of the fence line. My question
would be, can I feed this wire from 50 ohm coax at the house end? What
kind of matching network would be needed at the antenna? Would a
matching network be needed at the antenna, or can I use an antenna
tuner in the shack only? I am trying to avoid a center fed dipole, as
I would require a center strain relief pole in the center of the back
yard. This is a city lot, were the property is longer than it is wide.
Also, would a counterpoise be needed, and can you explain to me what a
counterpoise is, what it is made of, and it's purpose? Any suggestions
appreciated. Any pointing to further info is appreciated.
Thanks,
Paul

On 25 Mar 2004 06:56:04 -0800, Paul stood up and said:
Hello, I am looking to put up my first HF antenna. I have considered a
trap dipople in the attic, but seeing this is a one story house and
only 25 feet long it would only be about 15 feet off the ground and
more trap than radiator. I have also considered a mass produced
verticle to go on the existing tripod on the roof, but as I am
currently on medical leave it is not in the budget. My plan is to run
an approximately 80 foot wire from the existing tripod on top of the
house length wise accross the backyard to either a pole erected at the
fence line, or a tree on the other side of the fence line. My question
would be, can I feed this wire from 50 ohm coax at the house end? What
kind of matching network would be needed at the antenna? Would a
matching network be needed at the antenna, or can I use an antenna
tuner in the shack only? I am trying to avoid a center fed dipole, as
I would require a center strain relief pole in the center of the back
yard. This is a city lot, were the property is longer than it is wide.
Also, would a counterpoise be needed, and can you explain to me what a
counterpoise is, what it is made of, and it's purpose? Any suggestions
appreciated. Any pointing to further info is appreciated.
Thanks,
Paul

Sounds like a job for a random wire antenna tuner. I've never used one
but I do know some people who have and with good success. As the name
suggests, you simply connect a length of wire to the tuner and tune it to
the band you want to transmit on. I suppose you could use the center
conductor of a coax as a feed to the wire. MFJ sells these tuners. You
could probably find one at a ham fest as well.

Paul wrote:
My plan is to run
an approximately 80 foot wire from the existing tripod on top of the
house length wise accross the backyard to either a pole erected at the
fence line, or a tree on the other side of the fence line. My question
would be, can I feed this wire from 50 ohm coax at the house end? What
kind of matching network would be needed at the antenna?

Is this a single band antenna?
--
73, Cecil http://www.qsl.net/w5dxp



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You have two options.

(1) Locate an automatic remote-controlled tuner, outdoors, between the end
of the antenna wire and the coax line to the shack.

(2) Bring the antenna wire right into the shack and use an ordinary manual
tuner between the antenna wire and the rig.

You'll probably notice little difference between the two. And what
difference there is will be due to the different lengths of a random antenna
wire.

For a single-band antenna just connect a fixed L-match network between
antenna and coax or between antenna and rig.

Whatever you do you will need a ground. A counterpoise is a sort of
poor-man's artificial ground. It is a horizontal wire a few feet above
ground level and has resonant properties. Just a single low radial. It is
really a part of the antenna.
----
Reg, G4FGQ

Reg Edwards wrote:
Whatever you do you will need a ground. A counterpoise is a sort of
poor-man's artificial ground. It is a horizontal wire a few feet above
ground level and has resonant properties. Just a single low radial. It is
really a part of the antenna.

Yep, a lossy part.
--
73, Cecil http://www.qsl.net/w5dxp



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"Paul" wrote in message
om...
Hello, I am looking to put up my first HF antenna. I have considered a
trap dipople in the attic, but seeing this is a one story house and
only 25 feet long it would only be about 15 feet off the ground and
more trap than radiator. I have also considered a mass produced
verticle to go on the existing tripod on the roof, but as I am
currently on medical leave it is not in the budget. My plan is to run
an approximately 80 foot wire from the existing tripod on top of the
house length wise accross the backyard to either a pole erected at the
fence line, or a tree on the other side of the fence line. My question
would be, can I feed this wire from 50 ohm coax at the house end? What
kind of matching network would be needed at the antenna? Would a
matching network be needed at the antenna, or can I use an antenna
tuner in the shack only? I am trying to avoid a center fed dipole, as
I would require a center strain relief pole in the center of the back
yard. This is a city lot, were the property is longer than it is wide.
Also, would a counterpoise be needed, and can you explain to me what a
counterpoise is, what it is made of, and it's purpose? Any suggestions
appreciated. Any pointing to further info is appreciated.
Thanks,
Paul





Hi, Paul -

See The ARRL Handbook, 2002, 79th edition, page 20.17. There you will see "A
Resonant Feed-Line Dipole." What is shown is a 1/4-wave wire end-fed by 50
Ohm coax. A quarter wavelength from the wire/coax connection is a
several-turn coil made of the coax and then the coax continues toward the
shack another 1/2 wavelength.

This may not be what you want since it is resonant, I guess, for a single
band, but thot I would mention it.

John

"Paul" wrote in message
om...
Hello, I am looking to put up my first HF antenna. I have considered a
trap dipople in the attic, but seeing this is a one story house and
only 25 feet long it would only be about 15 feet off the ground and
more trap than radiator. I have also considered a mass produced
verticle to go on the existing tripod on the roof, but as I am
currently on medical leave it is not in the budget. My plan is to run
an approximately 80 foot wire from the existing tripod on top of the
house length wise accross the backyard to either a pole erected at the
fence line, or a tree on the other side of the fence line. My question
would be, can I feed this wire from 50 ohm coax at the house end? What
kind of matching network would be needed at the antenna? Would a
matching network be needed at the antenna, or can I use an antenna
tuner in the shack only? I am trying to avoid a center fed dipole, as
I would require a center strain relief pole in the center of the back
yard. This is a city lot, were the property is longer than it is wide.
Also, would a counterpoise be needed, and can you explain to me what a
counterpoise is, what it is made of, and it's purpose? Any suggestions
appreciated. Any pointing to further info is appreciated.
Thanks,
Paul

Paul,

If the reason you are really "trying to avoid a center-fed dipole" is
because you would need a strain relief pole in the middle, check your
premises. They are incorrect. You do not need any such strain relief pole. A
good high strength (5/16") dacron line with standing rigging at both ends
will hold any 1kw rated Balun nearly horizontal between two points much
farther than you have to reach. The line is the stain relief so the wire
antennas feel only their own weight. The dacron carries weight of the Balun
and the feedline hanging underneath it.

Tuning a randon wire will be a decent compromise unless a specific band or
frequency is your target, where the dipole, although directional, would
outperform it.

Jack
Virginia Beach

Paul,
Another suggestion, end feed a center fed dipole. That
doesn't
make much sense, but thats because I don't know how to describe
it.
In effect, run the coax ~through~ one half of the dipole to the
center where the feed point is. One way is to double the braid
back
onto it's self. The folded back braid makes up half the dipole,
the
center conductor is the 'other' half. I'm sure there are better
descriptions and pictures somewhere, I'll see if I can find one.
'Doc

Paul wrote
Hello, very ggod suggestion, I never thought of that. Now here is my
question to that. In using your idea of the dacron rope holding up the
antenna, can I run the coax parallel with the leg of the dipole along
the dacron rope that is closest to the house to the balun? Would that
give any ill effects? Or would the coax have to run along the ground
underneath the antenna and come up to the antenna and connect at the
balun at a 90 degree angle? I am trying to avoid lines or poles in the
middle of the backyard, little one is almost old enough to run around
backyard.
Thanks
Paul

Paul,

The little one pulling the feedline off the balun is a hazard not considered
in most antenna planning! Maybe that s/b a standard allowance in
line-strength and coax-connection type ;-)

I would avoid the radiation into a feedline that running alongside the wire
antenna would surely make. You could try letting the center-feed hang down
several feet below the antenna wire then draw it back up to the roof top and
henceforth down into the shack.

Maybe Doc's reply can elaborate how his compromise works, but it seems to
be a lot less efficient that the standard dipole, which would then send you
back to the end (or start) fed random wire idea.

Best,

Jack

'Doc wrote in message ...
Paul,
Another suggestion, end feed a center fed dipole. That
doesn't
make much sense, but thats because I don't know how to describe
it.
In effect, run the coax ~through~ one half of the dipole to the
center where the feed point is. One way is to double the braid
back
onto it's self. The folded back braid makes up half the dipole,
the
center conductor is the 'other' half. I'm sure there are better
descriptions and pictures somewhere, I'll see if I can find one.
'Doc
Wow, that is a very interesting concept. An antenna consisting of all
coax. That would solve a lot of configuration problems, and leave the
backyard clear of obsticles other than the antenna over head. Has
anyone had experience with one of these? Although that would be quite
a bit of coax for an 80 foot run, plus lead in to the shack, but that
would solve a lot of problems. What would the coax size have to be?
Could rg-8u be used? I wil have to check the cost though. Thanks for
the suggestions.
Paul