[TowerTalk] Coax Losses on 160 and 75?

[Jim Brown]

Gerald,

AC6LA's ZPlots implementation is an automated version of what Steve is 
suggesting. You measure S11 twice for some known length of the coax you 
want to test, first with the far end open and then with the far end 
shorted. This produces nulls, the depth of which depend on the loss in 
the line at the null frequency. You save each of these sweeps to a data 
file, then export them to ZPlots, which is an Excel spreadsheet that 
does the math.

So as I understand AC6LA's ZPlots, he computes the line loss from the 
nulls within the frequency range of that measurement for that length of 
line. These loss values are then matched to the computed loss from the 
equation for loss in a line to determine the constants for that equation 
needed to fit the values at those nulls. The fundamental equation is 
then plotted vs frequency. The equation for loss is from the trans lines 
equations, taking into account resistance of the conductors at the 
frequency of interest (including skin effect).  An easy place to see 
that loss equation is on a data sheet for Times coax. The numeric values 
in that equation are for that particular coax; what ZPlots does is 
empirically determine those values for the coax we've measured.

i'm sure that Dan will correct any errors in my educated guess. :)

This is pretty easy to do if you have any decent vector impedance 
analyzer that can export data and Excel running on a computer. It works 
with any of the AIM units, with my VNWA, and with other comparable 
analyzers. Download ZPlots, which is an Excel spreadsheet. Note that 
ZPlots does NOT work with Open Office and Libre Office spreadsheets, 
probably because it depends on Excel's macro language. ZPlots imports in 
several text data formats, including Touchstone .s1p. I don't know about 
other analyzers.

73, Jim K9YC

On Fri,8/12/2016 11:53 AM, TexasRF--- via TowerTalk wrote:
> And the results are intuitively obvious for even the most casual observer,
> right?
>   
> The pdf mentions 1/4 and 1/8 wavelength multiples. Can we take it that
> random lengths do not work for the concept?
>   
> 73,
> Gerald K5GW
>   
>   
>   
> In a message dated 8/12/2016 1:41:50 P.M. Central Daylight Time,
> steve at karinya.net writes:
>
> http://www.karinya.net/g3txq/wet_ll/tl_formulas.pdf
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>