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Author Topic: Mixing Different Types of Coax  (Read 1270 times)
AK4SK
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Posts: 150




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« on: January 11, 2013, 10:50:22 AM »

When is it OK and not OK to use different types of coax between a radio and the antenna? In my station I use RG-8X between the radio and tuner, between the tuner and a bias-t for a remote switch, and from the switch to the inside of my entrance panel. From the outside of the panel to the remote switch I use LMR-400 and from the switch to the feed point is also LMR-400.

I have read that it is bad to mix coax but I have also read about people using short lengths of a different type of coax than the main feed line for jumpers in the shack. I'm just looking for clarification of when coax should definitely not be mixed and when it is OK.

Thanks,
Chris
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WB6BYU
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Posts: 13355




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« Reply #1 on: January 11, 2013, 11:09:24 AM »

Mixing coax types with the same impedance isn't a problem.

The power rating will (typically) be that of the weakest link.

The loss will be the total loss of all the sections combined.


You do have to be a bit more careful combining coax of different
characteristic impedances because you can get some impedance
transformation affects, depending on the lengths involved.
Sometimes this is done intentionally, for example, a quarter wave
of 75 ohm coax as an impedance matching section between a
112 ohm loop and 50 ohm coax.  If you just use random lengths
of 50 and 75 ohm coax you could end up with an SWR over 2 : 1,
even with a 50 ohm load on the other end.  But in many cases
the 75 ohm coax has lower loss, and may result in more radiated
signal regardless of the mismatch.
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AK4SK
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Posts: 150




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« Reply #2 on: January 11, 2013, 01:37:07 PM »

Thanks for the info. I thought that what I was doing was fine but when I was thinking about it recently I was unsure.
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