N connectors are air dielectric coaxial transmission lines where they
mate. Impedance for an air dielectric coaxial line is:
Z0 = 60 ln(r0/ri)
So, a 75 ohm center conductor (ri) is necessarily smaller in diameter
than a 50 ohm center conductor for a given size shield diameter (r0).
If you mate a 50 ohm male N connector with a 75 ohm female N connector,
the usual result is to break one of the leaves of the center conductor
on the female connector.
The same does not apply to typical BNC connectors, as the 50 ohm BNC
has a teflon dielectric, but the 75 ohm BNC has an air dielectric, so
the center conductors are the same diameter.
More than you wanted to know.
-Chuck Harris
peter bunge via Groups.Io wrote:
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Hi Steve, an HP8714B just sold for $565 US.
I suspect you paid much less for the 75 ohm version and as much for
shipping..
My suggestion is to keep it and use it with 75/50 pads to learn about it
while watching for a cheap 50 ohm version, not working if you have repair
abilities, and use your 75 ohm version to troubleshoot and repair.
Do you have the pads? I have a couple of new Greenpar 502-4718-701, 90-48
that you can have for the price of shipping. Contact me offline.
Be aware that the 75 ohm Type N are different from the 50 ohm Type N and
you could damage them by attaching the wrong one. Someone else may have a
better explanation but 75 ohms seems to explain the different dimensions.
PeterB
[image: 75_50 ohm pads.JPG]
