Re: [TowerTalk] N connectors

[Chuck Counselman <ccc@space.mit.edu>]

The overriding issue for me is whether a connector can handle 
legal-limit power at high SWR (e.g., = 15), 'cuz sometimes this is 
how I operate; and everything else in my feed system [incl. 
power-amp, LPF, dir. couplers, common-mode chokes, tuner(s), 
balun(s), lightning-protector(s), and the coaxial cables themselves] 
_can_ take it.

In Amphenol's spec. sheet for the type N connector 
<http://www.amphenolrf.com/products/typen.asp>, the maximum 
continuous power rating is 600 W.  At what frequency is not stated. 
If we assume that this value of power refers to f = 11 GHz and that 
the max.-power rating is inversely proportional to frequency because, 
due to skin effect, resistance is inversely proportional to 
SQRT(frequency), then the max.-power rating at 30 MHz would be about 
20 times greater, i.e., 12 kW.

Twelve kW may sound like a lot, but it corresponds to an RMS current 
of 15.5 A, which is less than you can get with legal-limit power and 
SWR = 15.

A type N connector is rated for higher _voltage_ than a UHF 
connector, but _current_ is the limiting factor.  The problem is the 
small size of the center pin in a type-N connector.  The specified 
resistance of this pin connection is 1 milli-ohm.  The power 
dissipated in 1 milli-ohm by an RMS current of 15.5 A is 0.24 W.

-Chuck, W1HIS
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