Subject: Re: How to check for a 50 or 75 ohm connector
Date: Sun, 22 Dec 2002 01:58:44 -0800
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I have a large box of mixed BNC connectors/tees
Using the simplest equipment possible
(multimeter?) HOW do I check if
the connector is for 50 Ohm or 75 Ohm coax
connection. There are no
At the risk of oversimplifying things....
If you can't tell the difference it don't matter.
Stated another way, if a multimeter is the best
you can do, it's
unlikely that you'll be able to tell the
difference in any application
that you have the instrumentation to measure.
It'll take some doin'
to create a situation where the connector
Any application where a centimeter of
discontinuity from 50 to 75 ohms
matters, probably shouldn't be using a BNC anyway.
For most applications, reach into the box, pull
one out, and use it.
If you think that random hunk of coax is really
50.0 ohms, you also have
a surprise coming. Six feet of 52+/- ohms will
have way more effect than
1cm of 75 ohms in most 50 ohm systems.
Having said all that, if you have access to a high
resolution computer monitor
with high quality BNC input, you can install one
of your unknown connectors and
look for ringing on vertical lines. Use the green
input, cause it has the most
visibility. It's like a 75 ohm TDR with higher
resoluton than the
scope that most of us can afford...but still not
sure you'll be able to tell the
diff between connectors.
I got curious and put a 50 ohm elbow connector on
the 75 ohm green input.
at 1280x1024 resolution, I can't see ANY
difference with a 25X microscope.
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