[TowerTalk] Ameritron Remote Controlled Switches

w8ji.tom w8ji.tom@MCIONE.com
Mon, 09 Nov 1998 10:20:49 -0500

Hi Steve,

> Why would UHF connectors handle high power better than N style connectors
> in your RCS-8 series coax switch?  Comparing the data I have from
> on their UHF and N connectors, this might seem otherwise for their
> "standard" models.  The voltage rating for the N is far greater, and I'd
> like to think both connectors can intermittently handle 10 amps or less
> RF at the 5 KW level or below. 

The voltage rating might be greater in catalogs, but in real world hi-pot
tests N connectors always arced at much lower
voltage than properly assembled PL-259's!! The biggest problem in the
connector is arcing across the surface of the insulation at the base of the
male center pin.

If you look inside a male N connector, you'll clearly see the weakest
point. It is the very small air gap between the center pin and the grounded
shield connection surrounding that pin. Air gap is .070 inches or less in
most connectors, and it is all air with NO helpful dielectric!

In contrast the closest air gap in a standard PL-259 - SO-239 combo is
about .15 inches! That gap is on the face of the SO-239. That is the
"weakest point".

A secondary problem is the poor current handling capability of the N. It is
far worse than the 239/259 combo. The pins are smaller in OD, and have less
mechanical tension. That results in localized heating and eventual failure
in the center pin mating areas from loss of tension in the female spring

> "UHF" Connectors:  rated for 500 V Pk and DC to 300 MHz with their
> model
> vs.
> "N" Connectors:  rated for 1,500 V Pk and DC to 11 GHz for their TFE
> Has your experience at these power levels shown otherwise?

Absolutely. I have no idea how they tested the connectors to derive those
ratings, but factually N connectors are always the weakest link in any HF
system. Good quality 259/239 combos will easily carry 10 kW ICAS power when
matched, and PTFE connectors will handle the limits of any cable you can
attach at HF. In contrast N connectors are puny weak problem sources. I
don't trust "N's at all for any sort of power, especially with a line

The only good use for a N connector is at UHF, in applications where
impedance is critical.... or when the connector needs to be weather
resistant without outside weather shielding. They are no better than a
standard BNC for power, current, or voltage handling.

73 Tom

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