Jeff Liebermann wrote:
On Mon, 7 Jun 2010 14:11:58 +0100, Gaius wrote:

In article fda40c34-830f-438d-830e-0c1c23d2bc44
@c10g2000yqi.googlegroups.com, says...

BNC's are still 50 or 75 Ohm. Old versions had different diameter
centre pins in order to acheive the correct characteristic impedance.
Can you (or anyone !) provide some evidence of this, in terms of actual
measurements or manufacturers' specifications showing a difference in
the "Old" versions ?

I downloaded the mechanical drawings from the Amphenol web pile and
found that the center pin diameter is missing from the drawings. I'll
look elsewhere when I have time.
http://www.amphenolconnex.com/products/bnc.asp

I have a box full of 75 coax patch cables I salvaged from a radio
station cleanup. They all mate fine with a 50 ohm BNC jack. The only
difference is that the 75 ohm plug has no dielectric, while the 50 ohm
jack does.



http://www.wbdg.org/ccb/FEDMIL/prf39012_16h.pdf is the MIL drawing for
the plug.
note they only have ONE drawing for the center contact.

They also call out MIL-STD-348 for the pin contact interface.
http://www.dscc.dla.mil/Programs/Mil...oc=MIL-STD-348
http://www.dscc.dla.mil/Downloads/Mi...8/idstd348.pdf
is probably the one you want.

on the plug/pin, dimension C (the ID of the insulation inside the outer
conductor) has a minimum, but no maximum.

Likewise on the socket, dimension E, which mates with dimension C on the
plug does have a maximum, but no minimum, implying you can have a "no
dielectric" version.

Dimension D on the plug (the pin diameter) has only one value 0.052 to
0.054 inches.

Dim M on the socket (OD of center conductor) is 0.081 to 0.089,
presumably to correspond roughly with dimension R on the plug, which is
the same.