What is with you and the swr meter? Forget it. Make a dipole and hang it
up.Make a groundplane and hang it up. Get a cheap 1/4wave commercial mobile
whip, cut it 19" long, stick it on a metal bracket and screw it to the house
gutering. Bandwidth is so wide at VHF you won't have a problem. I've never
bothered with an swr meter at VHF. The formulas work.

Brad.

"tom" wrote in message
news:LeZZd.695607$Xk.128464@pd7tw3no...
My other cohort suggested a ground-plane vertical, too. What's the deal
with ground plane verticals? It seems they are slightly mechanicaly more
complicated than a half wave dipole, but that's fine if there's some
advantage. Are they safer to use without an swr meter?

I just checked the owners maual, and it does have protection circuitry.

--
73
Tom H
VA7FAB

Now that's a good idea --- I'll just have to make sure I don't jab
anyones eyes out on the subway (I'm car-less in Canada). I'm trying
to imagine just how bulky it will be, hmmm --- I should be able to
manage it, I think.


1/8" brass welding rod is soft. If I were you, I'd cut the elements long
enough to turn the ends into little loops, for eye protection.


Ed K7AAT

I believe the original poster wanted to know how to create a dipole. If you want to make a dipole
with a vertical configuration, you have to use a method which keeps the radiators vertical and the
feedline horizontal for some part of a wavelength. Try this:

Make a TEE shaped assembly of PVC pipe using a TEE connector, one piece of PVC about one metre long
and two pieces of PVC about 25 centimeters long. The longer pipe mounts horizontally and the
shorter pipes are oriented vertically. Cement all the pieces into the TEE. Strip the outer jacket
off a length of RG58 about 20 inches from the end. Make an opening in the braid next to the outer
jacket and pull the center conductor through so that the braid and center conductor are sepatate.
Push the RG58 into the long pipe and make the center conductor bend up into the upper vertical PVC
and pull the braid down through the lower vertical PVC. If necessary, prune the center conductor
and braid for best SWR, but the SWR should probably be low enough as is.

-ken-

I get it, and then maybe once it's all set, I could put end-caps on the top
and the bottom of the vertical segment to keep it dry. Maybe it would be
good to put in some kind of fastener, too, holding the flexible braid
immobile against the interior of the downward-pointing vertical segment ---
before the installation of the end-caps, obviously.
I like it --- simple but effective.
But does the horizontal segment have to be an entire meter, though? I think
I can remeber seeing those T-like, FM antennas mounted on large towers but
with horizontal segments that were shorter than a meter --- I think they
were slightly shorter than the vertical segments.

--
73
Tom H
VA7FAB

On 17-Mar-2005, "tom" wrote:

I get it, and then maybe once it's all set, I could put end-caps on the top
and the bottom of the vertical segment to keep it dry. Maybe it would be
good to put in some kind of fastener, too, holding the flexible braid
immobile against the interior of the downward-pointing vertical segment ---
before the installation of the end-caps, obviously.

Yes, I omitted those refinements as sort of obvious.

But does the horizontal segment have to be an entire meter, though? I think
I can remeber seeing those T-like, FM antennas mounted on large towers but
with horizontal segments that were shorter than a meter --- I think they
were slightly shorter than the vertical segments.

I chose the one meter length arbitrarily so that it would be about a half wave. The idea is that
the feedline should be kept at right angles to the radiator for some distance. A coil of coax where
the feedling exits the PVC might be a good idea to reduce coupling.

73,
-ken-

If the idea of the coiled-feedline balun is to prevent the outer braid from
turning into a radiating element, wouldn't it be preferable to position the
coils in the feedline next to the antenna feedpoint instead of at the
opposite end of the horizontal segment? Or would there be harmfull,
inductive coupling to the the coils if they were that close to the
feedpoint?
Also, if one were to use a ferrite-bead type balun (not the type that the
feedline is wrapped around) instead of a coiled-feedline type balun, do you
think it would it be necessary to have electrical contact between the
ferrite-bead and the outer braid (necessitating stripping the outer
insulation)?


--
73
Tom H
VA7FAB

Tom, you are making this waaaay too complicated. Just solder up a
ground plane on an SO-239, hook a coax to it and start transmitting.
You don't even need welding rod. I have used coat hanger wire in the
past. Forget about baluns, beads and inductive coupling. We're not
launching a spacecraft here. Keep it simple.

Dick - W6CCD

On Fri, 18 Mar 2005 20:17:24 GMT, "tom" wrote:

If the idea of the coiled-feedline balun is to prevent the outer braid from
turning into a radiating element, wouldn't it be preferable to position the
coils in the feedline next to the antenna feedpoint instead of at the
opposite end of the horizontal segment? Or would there be harmfull,
inductive coupling to the the coils if they were that close to the
feedpoint?
Also, if one were to use a ferrite-bead type balun (not the type that the
feedline is wrapped around) instead of a coiled-feedline type balun, do you
think it would it be necessary to have electrical contact between the
ferrite-bead and the outer braid (necessitating stripping the outer
insulation)?

Check with your local club and see if someone has an swr meter you can
borrow. Most clubs are happy to help out.


Jeff
KBØGVI

I just got the rig all set up a few minutes ago with a vertical
groundplane --- a design I chose because it obviated the need for any kind
of matching due to it's intrinsic, unbalanced 50 ohms impedance. Works like
a charm too, thanks to everyone for all the excellent advice, its very much
appreciated.

--
73
Tom
VA7FAB
Skype Name:
va7fab_tom_in_vancouver