[TowerTalk] Understanding Coax Loss Measurements

[Jim Brown]

On 11/30/2020 12:44 PM, Kirk Kleinschmidt via TowerTalk wrote:
> I may have improperly used my power ratio to decibels calculator.:)
> With exactly 10 W going into the cables, I measured
> 8 W out (RG-11); 7.2 W (RG-213); and 7 W (RG-6) at 30 MHz.
> Upon reflection (pun intended), my 2.8 dB figure can't be correct...

We can't use a 50 ohm wattmeter to measure loss in 75 ohm cable, thanks 
to the standing waves resulting from the mismatch. A study of how 
transmission lines work is advised. See the ARRL Handbook and Antenna Book.

What DOES work is the method I outlined earlier with AC6LA's spreadsheet 
and a properly calibrated Vector Analyzer.

73, Jim K9YC