BNC - now I've seen it all ...

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A quote from the Cabletron Systems Cabling Guide:

    "Building Network Coax (BNC) connectors ...."

Add one more reputed explanation/definition of BNC.

Re: BNC - now I've seen it all ...



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"Reputed"? I don't think so.

MrT.



Re: BNC - now I've seen it all ...



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Indeed. I had a trainee radio tech try to tell me that a BNC connector was
both 50 and  75 ohm compatible.

Jason



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Jason James wrote:
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   There are 50 Ohm and 75 ohm versions.  IBM used 93 ohm RG/62 coax
with BNC connectors for terminals, as well.  The pin diameter is
different, to maintain constant impedance.


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Re: BNC - now I've seen it all ...



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Yeah,,..he thought a 50 ohm BNC was good for 75 as well.

 IBM used 93 ohm RG/62 coax
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93 ohms!  I wonder why? Guess you could use 50 ohm test equip etc and dial
in the mismatch loss.

Jason



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err, it was IBM. If you understand, then you'll know.
If you don't, think lock in with proprietary HW.
All the dinosaurs did it.
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Re: BNC - now I've seen it all ...



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Apple have been making a fortune that way for years, and have yet to become
extinct. They even change their own products to prevent accessories from
some models working with others. The lambs keep lining up to buy however.

MrT.



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Apple is a mere amateur.

but you are correct.
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Re: BNC - now I've seen it all ...



Jason James wrote:
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   They used 93 ohm coax to minimize line loss.  That way they could run
hundreds of feet between the concentrator and the terminals.  The
alternative was RS-232, at lower data rates.


--
You can't have a sense of humor, if you have no sense!

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A their site
http://www.amphenolrf.com/products/bnc.asp?N=0&sid46%B11E806D75617F ,
Amphenol say about their BNC connectors: '50 ? and 75 ? connectors are
intermateable to ensure non-destructive mating'.

Chris



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... further proof at
http://www.amphenolconnex.com/SearchResults.asp?ProductID19%1 wherein:
'Center contact .053" diameter, 30" Au. True 75 ohm'.  Compare with:
http://www.amphenolrf.com/PDF/grouped/bnctnc.pdf where the mating diameter
of the pin of a 50 ohm BNC plug (or TNC) is given as 0.052 to 0.054 inches.

It's the PTFE components that are different between the two impedances - the
75 ohm components have more air between the mated inner and outer parts.

Chris



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christofire wrote:
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   I was referring to the ratio of OD of the pair of center contacts to
the ID of the shell.  That is what determines the impedance.

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The diameters of the mating parts are the same for 50 ohm and 75 ohm BNCs
according to the Amphenol BNC catalogue at
http://www.amphenolrf.com/PDF/grouped/bnc.pdf .  Compare the drawings on
pages 107 and 124.  The difference is the PTFE 'filler' between the mating
parts in the 50 ohm case.

The pin diameter behind the mating part is different for the two cases, but
that has no bearing on whether the parts can be mated without damage.

Chris



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christofire wrote:
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   Sigh.  What a waste of time.  I have bought & used both types for
over 30 years.  I don't need the damn data sheets.  I have paper copies
from the thousands I've used.

   I didn't say the mating parts were different in the Amphenol parts.
I explained what determines the impedance.  



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Re: BNC - now I've seen it all ...


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Well, for some applications it my not make a difference....

geoff



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Not until after you try mating a 50ohm male with a 75 ohm female :-)

MrT.



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geoff wrote:
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   At low frequencies, it won't.  Try a 100 foot of 50 ohm cable for
video and see how much detail you lose compared to RG/59 or RG/6.  We
had both 50 and 75 Ohm output options in our telemetry products.  A six
foot cable would made a good module look bad when you used a 50 Ohm
cable on a 75 Ohm port.


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