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impedence match

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Subject: impedence match
From: (Bill Cotter)
Date: Mon, 23 Sep 1996 12:24:16 -0400

There was an interesting article in Ham Radio magazine several years ago on
just this topic. The author used a section of 1/2"(?) copper tubing (approx.
20") as an outside sleeve and 3/16"(?) (approx. 19") copper tubing as an
inner conductor to construct a 62.5Z quaterwave matching transformer for
each end of the CATV hardline. This clever arrangement made a convenient
low-loss matching section as well as an inexpensive SO-239 adapter. 

The construction is relatively simple:

        The center conductor of a modified SO-239 (mounting ears removed to
        form a cylinder) is soldered to one end of the inner-tubing conductor.
        The center-pin receptacle from a second chopped-up SO-239 is soldered
        to the opposite end. The outer-tubing section is slotted (approx. 1/2")
        at the hardline end for a compression clamp. Slide the inner-tubing
        assembly into the outer-tubing and solder the modified SO-239 to the
        NOT-slotted end.  After the section is assembled, the inner-tubing
        receptacle fits snugly over the hardline inner conductor. The
        outer-tubing clamp is tightened and the entire assembly is

I don't recall how he prevented oxidation between the Al/Cu junction.
Probably some sort of conductive, corrosion inhibiting jelly similar to that
used in AC power line connections. In our area of the country there are
ample supplies of free "tag ends" from the cable TV companies. They are
generally 100-250 ft in length, some with pvc jabbering and make excellent
VHF/UHF feedlines.


Bill, N4ALG

At 07:10 PM 9/22/96 -0400, Bill Rininger wrote:
>I have some 72 ohm hardline I would like to use for feedline.
>It is about 1/2 inch in diameter.
>I am looking for a way to construct a transformer to match it
>to 50 coax for 2 meters.
>Any ideas would be appreciated.
>FAQ on WWW:     
>Administrative requests:
>Sponsored by Akorn Access, Inc & KM9P

 Bill Cotter, Manager, NEOC_LAN           Mail:
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 University of Kentucky                   FAX:    (606) 257-9009
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