[TowerTalk] Open wire measurments

[Wes]

Paul,

I have a number of analyzers, the gold standard DG8SAQ, the FA-VA5, the 
RigExpert AA-55 Zoom, the EU1KY FAA-450 and a coax bridge used with my HP 8405 
Vector Voltmeter, but I do not have the CIA, so can't speak to it.

Having written about measuring window line a number of years ago when I had 
access to an HP-8510, which didn't cover HF, I decided to remeasure some line 
with HF equipment that I now own and with some hindsight and new computational 
tools.  Since we tend to quote things (in the colonies) in dB/100 feet, I 
decided to actually measure 100' of line as I mentioned previously.  As I don't 
have 100+ feet of air-conditioned space I was doing this outside and the WX was 
simply too toasty to do extensive tests at that time.  (I intend to revisit this 
when it cools off, November maybe.)  Nevertheless, my preliminary measurements 
showed that, even with the AA-55, completely battery-powered analyzer, some 
common-mode choking stabilized the results.

I have no doubt that less reflective loads can be adequately measured without 
common-mode suppression, but my task has to handle 100% reflections and do it 
pretty accurately.

Wes  N7WS

On 9/3/2019 1:30 PM, Paul Christensen wrote:
> Wes,
>
> "As has been suggested elsewhere in this thread, you might be tempted to try connecting the balanced line to the unbalanced test port of the analyzer, in the belief that since it is a "floating" device it's also "balanced".  This has not worked for me."... "So the line radiates; it's part transmission line and part antenna."
>
> No argument there, but that doesn’t mean the CIA cannot report back a valid impedance measurement.  I have yet to find an instance where it hasn’t worked with a complex Z on a balanced line.   I routinely reverse the balanced termination on the unbalanced reflection port and achieve the same result.  Moreover, I obtain the same (or nearly the same) result when using a 1:1 Mini-Circuits RF transformer, then OSL calibrate after the transformer.  By contrast, I often cannot obtain identical results when changing line polarity when: (1) using a "bench" type VNA device where powering comes from electrical mains; and (2) a transformer isn’t used.
>
> Paul, W9AC
>
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