[TowerTalk] Understanding Coax Loss Measurements

[Edward Mccann]

Thanks for your input Jim B.

Ed McCann
AG6CX

Sent from my iPhone

> On Nov 28, 2020, at 5:14 PM, Jim Brown <jim at audiosystemsgroup.com> wrote:
> 
>> 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
> 
> 
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