W7TI wrote:
Has anyone ever made their own hardline? I'm thinking 1/2 inch copper
water pipe with a center conductor supported by some plastic discs
spaced every so often. You might not get it exactly to 50 ohms but I'd
think the loss would be so low it wouldn't really matter.

Comments?

It's certainly possible - and regularly done for short quarter-wave
impedance transformers at VHF/UHF - but there are practical problems for
making long runs: difficulty of obtaining center rod in long lengths,
has to be built on-site, difficulty of splicing, standard connectors
have to be adapted... and in the longer term: internal condensation and
corrosion, difficulty of repairing...

Those are just a few problems that come to mind ,from experience with
using shorter lengths outdoors in a damp climate (though you wouldn't
think it right now in England).

Except for those special-purpose applications, it really isn't worth the
trouble. It's easier to turn detective and find surplus sources of
hardline such as 50-ohm Heliax (used at cellular sites world-wide) or
the 75-ohm hardline used in the USA for cable TV.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

With so much 1/2" and 3/4" end of reel scraps at your local cable TV
franchise (most for free - to cart away) -
the disposal guys charge the CATV companies to take it away !!

The number of web links (amateur web pages) should give you an idea of how
many hams are using the CATV cable - especially
for VHF and UHF frequencies !

http://jonz.net/W3DHJ/catvhardline.html

http://www.n1bug.net/tech/catvline.html

http://www.rogerhalstead.com/conn.htm

http://www.qsl.net/k4pwo/connector.htm

http://www.repeater-builder.com/rbtip/w8zd.html

http://www.mindspring.com/~daverice/radio/hardline.htm

http://www.repeater-builder.com/rbti...gineering.html

http://www.qsl.net/n9zia/wireless/ha...onnectors.html

w9gb

"W7TI" wrote in message
...
Has anyone ever made their own hardline? I'm thinking 1/2 inch copper
water pipe with a center conductor supported by some plastic discs
spaced every so often. You might not get it exactly to 50 ohms but I'd
think the loss would be so low it wouldn't really matter.

Comments?

--
73, Bill W7TI

I've made a short section (12") of hard line for a MW dish feed. It's no
easy task! size relationships are critical and there's no easily available
material for the center conductor the right size for 1/2" copper pipe. I
ended up using hobby brass tubing for the project. The transition between
the center conductor and the connector is a bit finicky, too. Forming the
taper is a pain! The return loss is 7 at 3gHz, not great, but usable. In
short, the suggestions about CATV hard line are good ones, The 3/4 " works
up to 5 gHz with reasonable losses and that's with home brew connectors.

Good luck!

Phil, KB2HQ

"G.Beat" wrote in message
news:J_g%a.152188$o%2.65532@sccrnsc02...
With so much 1/2" and 3/4" end of reel scraps at your local cable TV
franchise (most for free - to cart away) -

On Thu, 14 Aug 2003 21:13:49 -0700, W7TI wrote:

Has anyone ever made their own hardline? I'm thinking 1/2 inch copper
water pipe with a center conductor supported by some plastic discs
spaced every so often. You might not get it exactly to 50 ohms but I'd
think the loss would be so low it wouldn't really matter.

Wellll....

The stuff isn't that difficult to make.
Making it correctly is something else.

OTOH, with half inch I think you will find the loss is not as low as
you have been thinking.

With half inch connectors are fairly simple to make.
Splices are also relatively easy to make if you have a lathe.
The commercial stuff uses gasketed brass rings with at least 4 screws
through the flanges to hole the sections together. The center
conductor can be joined using a threaded fitting, or just soldered
with the outer conductor slid back.

BUT as to the practicality of using hard line...
You need the proper spacing for the spacers
Breakdown voltage is less than for coax cable the same size with foam
or solid dielectric.
Copper oxide will become a problem unless the feed line is "purged"
with dry Nitrogen.

Typically the coax is *almost* air tight. It is purged with a very
low flow and pressure of dry Nitrogen. IF the flow increases and or
the pressure drops you know three is a problem.

Don't purge it and it *will* develop problems sooner or later. If you
live in a hot dry climate this might not be much of a problem.

IF you make your own, it will probably still cost twice as much as
good coax.

IF you are looking at saving money, or coming up with a good "low
loss" cable try (as others have already suggested) the 75 ohm TV hard
line. It's usually free, works great, you can easily find 1/2 inch
and 3/4 inch. I understand 1 inch is also available.

It's relatively easy to make connectors for the 1/2 inch and 3/4 inch.
I'd think the same approach used for the 3/4 inch would work for the 1
inch.

The only drawbacks are the difficulty of making short radius turns,
care in handling it, and the 1/2 inch is relatively fragile. The 3/4
inch and up is pretty rugged but still requires care in making bends
or it will easily "kink" which pretty much renders that piece useless.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Comments?

I remember one case where making coax was done and was appropriate. It
was a line that was several inches in diameter and probably no more than
20 meters long. The purpose that it served was to "feed" an end-fire
array of loop receiving antennas (along the line's length). The reason
to use the line was to have a VF that was as close to 0.99 as possible
so as to phase the distributed elements as optimally as possible.
Attenuation and power had nothing to do with the issue.
The result was a unidirectional pattern. One in each direction
depending on which end one connected to. Three of these fellows (and
six connections) made a reasonable direction finder with an
instantaneous beam every 60 degrees.
Life is much too short for one to use anything other than Heliax (or
TV cable) for the "normal" radio uses.
73 Mac N8TT
P.S. The fellows who replicated the Luxemburg effect with extremely
high power were said to have made their transmission lines out of
irrigation pipe. They must have had much more time than money.

--
J. Mc Laughlin - Michigan USA
Home:

"Ian White, G3SEK" wrote in message snip

Except for those special-purpose applications, it really isn't worth
the
trouble. It's easier to turn detective and find surplus sources of
hardline such as 50-ohm Heliax (used at cellular sites world-wide) or
the 75-ohm hardline used in the USA for cable TV.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

W7TI wrote:
TX 4:1 BALUN OPEN WIRE LINE 1:4 BALUN YAGI

Why don't you make the open-wire line an even number of half-wavelengths?
Then all you need is a 1:1 choke at the transmitter. No loss in the
baluns at all because there aren't any.
--
73, Cecil http://www.qsl.net/w5dxp



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W7TI wrote:

W5DXP wrote:
Why don't you make the open-wire line an even number of half-wavelengths?
Then all you need is a 1:1 choke at the transmitter. No loss in the
baluns at all because there aren't any.

I'll give it a try. Thanks.

The spacing of 450 ohm window-line might be better for 6m than the
3"-6" spacing of open-wire line.
--
73, Cecil http://www.qsl.net/w5dxp



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On Sat, 16 Aug 2003 16:20:06 -0700, W7TI hath writ:

Ok, since what I'm really after is low loss (not necessarily shielding)
how about this:

TX 4:1 BALUN OPEN WIRE LINE 1:4 BALUN YAGI

Do you think the loss in the baluns would outweigh the reduced loss in
the open wire line? I'm looking at doing this on six meters where I
have a fairly long run of coax - about 120 feet. Surely someone has
tried this before.

How about CATV hardline? I'm using about 70 feet of the stuff for
6M and 2M. I'm using the 1/2" stuff for 6M and the 3/4" for 2M.
It should be FREE -- the Most Important cable characteristic. HI!HI!
No reason why you couldn't use the 3/4" stuuf on 6M -- tho', I think
it might be overkill.
As another posted mentioned (for open wire), you can cut it for
n-multiple 1/2 wavelengths, and use the Flexible Stuff for pigtails
at each end.

http://jonz.net/W3DHJ/catvhardline.html

HTH
Jonesy
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