[LarrysList] UHF Connector

Larry Staples larrystaples at mac.com
Fri Jun 10 11:26:52 CDT 2016

Fellow Hams,
An article about the supposed awful characteristics of the UHF connector comes up periodically.  Let’s take a look at the full picture.
I design high power RF medical equipment.  Which connector does it use?  N?  No.  The N connector center pin is not rated for the RF current at 1KW under moderate SWR.  Further, the voltage breakdown rating is also insufficient under those conditions.  What do we use?  Type “HN” or 7-16 DIN.  Both much more expense and less standard in the ham world.
But the old PL-259 meets the needed ratings.  As a bonus, the center pin is much more tolerant of mechanical abuse.  But what about this impedance being wrong thing?  It’s true, the PL-259 is not “constant impedance”.  What this means is, if you treat the PL-259 like a very short transmission line (piece of coax), that coax is not 50 ohms.  So, it is like you patched on a piece of the wrong coax, one half inch long.  What is the effect of this?  At HF, absolutely nothing.  At 50MHz?  Nothing.  At 146 MHz.  Sorry, still nothing.  At 450 MHz?  Well no real loss, but you might be able to detect it.  At 1296 MHz?  Well, OK, here it starts to matter.  That connector length has to be significant in terms of wavelength for the issue to matter.  For those so inclined at math, at what frequency is that half inch piece significant, lets say 1/20th of a wavelength?
So, the N connector is the better choice when used at good SWR, modest power, at 1296MHz and above.  But what percent of amateur use does this represent?  If you don’t mind mixing connectors in your shack, it’s a great one for your 40 watt 440 MHz FM rig.
What would I use when I wanted the same connector across a lot of equipment?  If price was no object, the 7-16 DIN.  But in the real commercial world, the PL-259.  That is why manufacturers choose them, both for ham gear and a lot of commercial equipment below 400 MHz.  Cheap, rugged, and right for the job.  And please try the crimped ones; they are very easy to terminate correctly.

Drew Vonada-Smith, K3PA
drew at whisperingwoods.org

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