[RFI] Another Solar Panel RFI System

[Jim Brown]

On 12/18/2022 11:56 AM, wx5l at charter.net wrote:
> The FCC's should not label harmful interference with an S-meters reference.

Right. An S-meter displays the voltage at the input of a receiver. Its 
reading, even if properly calibrated, tells us nothing about the RF 
field strength (in mV/m) at a specified distance from a noise source, 
which is the only meaningful measurement. That's because the voltage at 
the receiver input depends on the 3D gain of the antenna, where it's 
located, it's height above ground, its proximity to surrounding 
conductive objects and their geometry, and how it's oriented with 
respect to any given source.

Not only that, but Field strength decays with at different rates in the 
near field and far field, which is dependent on frequency and the 
geometry of the source. And sources have magnetic fields, electric 
fields, and electromagnetic fields. In the near field of most sources, 
the magnetic field dominates, transitioning to the EM field at greater 
distance, again based on frequency and geometry.

RF field strength meters include a receiver driving a voltmeter, with 
calibration to an antenna suitable for the frequency range where it will 
be used.

Calibrated field strength meters are not cheap -- the last listings I 
remember for units used by AM broadcasters to comply with FCC regs were 
in the $3-$5K range, ant that was 20 years ago.

Modern alternatives likely include RF voltmeters and spectrum analyzers 
with calibrated antennas for the frequency(ies) of interest.

73, Jim K9YC