[CQ-Contest] 62 ohm coax cable

David Pruett k8cc at comcast.net
Sun Dec 11 22:54:04 EST 2005


My entire station is fed with 75 ohm CATV hardline.  The homebrew yagis are 
all matched to 75 ohms at the load, then in the shack I use what is called 
an ASYNCHRONOUS TRANFORMER to bring the impedance back to 50 ohms.  First 
described (at least that I saw) in Ham Radio Magazine and the NCJ back in 
1978, it uses short lengths of 50 and 75 ohm to convert a 75 ohm load to 50 
ohms.  It looks like this:

50 ohm in ]================={}=================[ 75 ohm load
                 .0818w             .0818w
                 75 ohm             50 ohm

Because there are frequency-specific lengths of coax involved, it's 
obviously a single-band system.  I've had these for almost two decades at 
K8CC with no failures.  No ferrite involved, but you do tend to get a lot 
of practice installing PL-259s.

The lengths get long enough that on 160 and 80 I tend to use un-uns for my 
50:75 matching, but there is no reason why an asynch section wouldn't work 
there as well.



At 04:37 PM 12/11/2005, Rick Dougherty NQ4I wrote:
>Hi all is there such an animal as 62 ohm coax? I am trying to do some
>matching with my 50 ohm system in the shack with some 75 ohm cable tv
>hardline...maybe there are some other ways to make the cabletv hardline look
>like 50 ohms?? thanks de Rick nq4i

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