[TowerTalk] DB's, ad nauseam

[Tom Rauch]

> power levels at differing angles of radiation. We all know there is no
> such thing as a perfect mirrorlike reflection going on in the ionsphere.
> Indeed it varies not only time to time but also angle to angle and time to
> time. Sometimes it appears to be quite linear and sometimes very non
> linear. Its too simplistic to say that i raised my antenna gain 1 or 2 or
> 3 db, or whatever, and what i heard is an accurate representation  of that
> theoretical change. Sometimes, due to the non linear reflectivity, the
> change may actually be greater.

Non-linear reflectivity only occurs when the transmitters signal has 
moved all of the available charges in some area the reflective 
medium, and it runs out of charges to move.

The result is the signal re-radiation from the ionosphere no longer 
follows the transmitter power in a linear manner, the reflected 
power increases at a SLOWER rate than the transmitted signal! 

Reaching that effect requires ERP levels in the order of millions of 
watts.

If you are seeing some other effect, where the increase is more 
than the transmitter ERP increase, you have experienced a 
measurement error. It could be caused by QSB or poor meter 
calibration.

Sometime we also fail to consider we might be using the slope of 
the lobe of an antenna. Another antenna with about the same gain 
on the nose of the main lobe might actually have provide radically 
different gain at that off-peak angle.

The ionosphere is absolutely linear for power level changes at 
normal power levels.


73, Tom W8JI
w8ji@contesting.com

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