Rick,
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.
73,
Dave/K8CC
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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