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1-6 of 6 messages
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WB6BYU 75 ohm to 50 ohm converting
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by N0ZYZ on June 16, 2008
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Just wondering if you could explain number 4 below? Sounds interesting.
Charley
4) use 1/12 wave matching sections of 50 and 75 ohm coax
at each end to transform up to 75 ohms and back to 50 ohms
5) use wideband 50 : 75 transformers at each end
6) use shorted stubs or other methods to transform between
50 and 75 ohms.
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RE: WB6BYU 75 ohm to 50 ohm converting
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by WW5AA on June 16, 2008
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Matching to what is the question? With out any indication of the resistance of the load, I can't figure out what what this means. Am I missing something?
73 de Lindy
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RE: WB6BYU 75 ohm to 50 ohm converting
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by WA7NCL on June 16, 2008
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Read this:
http://ourworld.compuserve.com/homepages/demerson/twelfth.htm
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RE: WB6BYU 75 ohm to 50 ohm converting
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by WB6BYU on June 17, 2008
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Sorry it took me so long to respond, but it looks like you got the information you need.
If you have further questions, my email is listed in my eHam profile.
Good luck!
- Dale WB6BYU
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RE: WB6BYU 75 ohm to 50 ohm converting
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by N3OX on June 24, 2008
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I've done the twelfth wave transformer thing, it works quite well.
A tip; it is possible to crimp RG-59 F connectors onto several types of 50 ohm cable with decent results (though I backed most of mine up with solder.) Double-shield RG-55 (don't ask me where to get it, I just had some) works great in my application.
If you use cable with a small, solid inner conductor then it will go right into an F connector. I've also nearly succeeded in getting a good fit with a *compression* F connector on RG-8X and soldering a stiff copper wire to the center conductor to make that connection. The trick is that you need to fatten up the jacket a bit. The compression connectors slide a metallic bit under the shield and then clamp down radially when you compress them, holding the jacket and shield tight to the metal thing inside while simultaneously making a good mechanical connection to the jacket. You have to fatten up the RG-8/X jacket a bit to make it work; I haven't worked out all the details. I did it with electrical tape but I don't like that too much; it's been my experience that compressed multi layer electrical tape tends to flow a bit, but stay tuned.
I mention it because F connectors and F barrels are so cheap compared to most 50 ohm connectors... and of course, they're a snap to install on the 75 ohm cable you'll be using.
I bought my 75 ohm cable on a 500ft spool at Home Depot "RG-6/QS" ... it actually has some Carol part number that I don't remember right now... but as is the usual case with much of the cheap 75 ohm cable, it's hard or impossible to solder the shield... so I decided to try to use readily available F connectors on the 50 ohm cable instead...
Anyway, several twelfth wave transformers in daily use here, it's a good technique.
73,
Dan
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