[TowerTalk] NCDXF Vertical Performance @ 500 Feet

[Jim Brown]

On 5/10/2022 4:46 PM, Tony wrote:
> In some cases, the beacons signals came within 1 S-unit of other Yagi 
> equipped stations here in New York and New Jersey including my own. It 
> most cases it was within 2 S-units. I believe the remote SDR receivers 
> have calibrated 6db per S-unit S-meters so the readings should be fairly 
> accurate.

This discussion is missing multiple factors. S-meter readings are based 
on the voltage at the input terminal of a receiver, and one s-unit is 
defined as 6 dB, which corresponds to a 4:1 power difference. That's a 
VERY rough indicator. Two S-units is a 16:1 power ratio -- the 
difference between 1.6kW and 100W, or between 5W and 80W.

S-meter readings depend on its calibration and linearity, which has been 
notoriously bad as long as there have been S-meters.

S-meter readings also depend strongly on the antenna feeding the 
receiver, as well as vertical directivity, which is strongly dependent 
on its height AND terrain.

The post IS correct to the extent that Elecraft rigs and SDR receivers 
in general CAN be accurately calibrated and have good linearity. I've 
done that calibration for my two K3s and their attached P3s, using an HP 
generator as a signal source, and set the P3 display in dBm.

73, Jim K9YC