[TowerTalk] Understanding Coax Loss Measurements

[Jim Brown]

On 11/28/2020 2:10 PM, Edward Mccann via TowerTalk wrote:
> Thanks Jim:
> 
> But not sure which your “yes” addresses, part 1 or part 2?
> 
> 1. “If I use the VNA with direct input of ladder line, say nominal 450 ohm Zo, but with measured parameters more near 400 ohms, should I not run OSL calibration with a 400 ohm load prior to running the sweep?”

NO!  We are calibrating the analyzer to the measurement plane, which can 
be it's input and output terminals, or it can be a pieces of 50 ohms 
coax attached to one or both ports.

If I'm not mistaken, the SARK is a VIA, not a VNA.  -- A VIA (Vector 
Impedance anzlyzer) has one terminal, only measures S11. VNA a(Vector 
Network Analyzer) has input and output, can measure all four 
S-parameters (so it can measure the gain/loss of a two-port device).

> 2. “The response below seems to imply that calibration with a 50 ohm load will yield “good results for coax and two-wire line of any impedance?”

That's exactly what I said.

The potential issue with 2-wire line though is that if the analyzer is 
running from a computer, it can unbalance the line, so it should be 
seriously choked and floating from anything grounded.

73, Jim K9YC