At 08:14 PM 7/22/2006 +0000, Ed Stallman wrote:
>Hello Group, I ran two length of 3/4 inch 75 ohm CATV cable 200 foot each
>to my newly installed tower. one each for 6 and 2M ! What I'm looking for
>is an impedance transformer to match my radio/antenna, I believe a 62 ohm
>transformer. I remember seeing these somewhere made from copper water pipe,
>I think they were 1/4 WL? I've searched on the internet with no luck! can
>someone point me in the right direction with a URL or publication, ARRL VHF
>book. even the formula would be helpful for knowing the outside and inside
>diameter of the tubing.
>
>Thanks Ed N5BLZ
>_______________________________________________
Ed,
Since the ARRL VHF Handbook is not in print, I checked the RSGB VHF Manual.
They refer to a Cot (Co-Tangent) transformer which is two short pieces of
coax used to transform a 50 ohm line to a 75 ohm line.
You need a 29.3 deg of
From a 50 ohm system you need 29.3 deg of 75 ohm line followed by 29.3 deg
of 50 ohm line to the 75 ohm feed. You must take into account the felicity
factor in figuring the length of each line. 29.3 degrees is the same as
0.081 wavelength.
If you make the coax out of tubing, the formula for coax transmission line is:
Zo = 138log10 D/d
D= inside dia of outer shield
d= outside dia of inner conductor
Hope this helps.
Lee Scott - AA1YN http://www.aa1yn.com
Home of the VHF & Up Register http://www.aa1yn.com/vhf
Home of the VHF Talk chatroom http://vhftalk.aa1yn.com
Hooksett, NH
FN43gc52
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