On 6/26/18 5:47 AM, Charlie@thegallos.com wrote:
But then again, using bury-flex as an example, has 9.5 awg center conductor, or
.1079, or less than the N connector
73 de KG2V
The UHF connector has a larger diameter center pin (0.156") than the N
(0.1197"), so its current handling capability is (slightly) higher.
__
True enough. I think, actually, a better thing to look at would be the
"mating contact surface". In a N connector, I think the contact area is
between the faces of the two inner conductors - the pointy pin on the
plug is just to center into the pin on the receptacle side.
Take a look at the *RF* mating surfaces in the N
https://www.amphenolrf.com/media/wysiwyg/N-Type_Interface_Drawing.JPG
Skin depth in Copper at 7MHz is about 25 microns (0.001"). The center
pins are probably gold plated beryllium copper, and the conductivity is
probably about the same.
If we assume that most of the current is carried in a layer about 2-3
skin depths deep, just the outer surface of that 0.120" pin in the N
connector is carrying the current, and more importantly, the contact
area is a thin annulus, 0.120" OD, 0.116" ID - .002"* .75" (.118*2*pi)
If that connector is a bit dirty, or the mating surface is damaged or
off angle, then you've got a problem.
If you have an N where the female side center conductor is spring loaded
(2 slot or 4 slot), then you have the problem of the "prong" being
slightly bent, and not making good contact with the pin on the male side.
In the UHF connector, it's more like a pin plug in a banana jack. The
contact path is through the *side* of the pin on the plug. There's no
illusion of trying to carry the current in a constant diameter (constant
impedance) path, so the wiping and contact area is much larger.
And then, the similar thing applies on the shield side - there are
slotted/springy and non-slotted versions here. From an RF standpoint,
the mating surface is that little ledge inside the female, and the face
of the tubular part sticking out of the male. That face can be damaged
or roughed up, or even bent in a bit, so the contact area is reduced.
For the "drive across it in the mud" UHF connector, the shield contact
area is those sawteeth interlocking, and with an installer applying
force with pliers, that will deform to make good contact, even if
there's crud in there. and, again, no illusions about "constant impedance".
From a "lightning protection" standpoint, the outside of the cable
carries the current, and that's the screw thread and barrel, in both cases.
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