Eddie
Henry has more than one chart showing different things,
the chart with & without radials shows signal strength received at the rx antenna at a height of 10mtrs & sited 30kilometers from the sigma4,
across the top is the sigma4 height above ground in meters,
down the side is signal strength in dBm,
it shows that when the sigma is isolated from mast & coax,
radials increase signal strength by almost 2db when the sigma4 is 10mtrs above ground & that the radials advantage reduces the closer the sigma4 is to ground,
what part is confusing you Eddie ?.
If you want to see the software I used in action watch the video you posted with the guy testing chokes using sdruno software with his rspduo
[MEDIA=youtube]8vBlROYjvMs[/MEDIA]
the spectrum screen is scaled in dBm on the left & also has a bar graph s-meter,
look under the bar graph you will see dBm & snr.
