[TowerTalk] PL259 Insertion Loss?

[Paul Christensen]

> You can see every connector's impedance bump.  Not so with N 
> connectors....

You can with some "Brand X" Asian imports...

I recently made a set of precision OSL loads for use with a vector network 
analyzer.  The 50-ohm load was made using a 0.1% SMD resistor precisely 
fitted between the BNC's center pin and shell.

When checking return loss across a sample of five Asian BNCs, the 
repeatability was horrible.   For example, I could calibrate using one load 
and attain 60-90dB as I swept from 500 kHz to 60 MHz.  If I switched to an 
identical load, return loss degraded to 20 dB and in one case, return loss 
would change substantially with the slightest pressure applied to the 
connector.  These changes are indicative of QC problems.  The connectors 
look well made to the eye but are in fact an electrical performance 
disaster.

However, when switching to Amphenol brand BNCs for the test load samples, 
repeatability was excellent with no more than a couple dB variation.  When 
you're up in the 60+ dB return loss area, nearly any mechanical change will 
be magnified under this test so it's important to maintain top QC.

This one test alone made me a believer in paying a bit more for 
quality-controlled connectors, regardless of whether they're 
constant-impedance types or not.

Paul, W9AC