On Dec 31 2008, 4:10*pm, Roy Lewallen wrote:
dBi is more than just dB. It's field strength (in dB) relative to a
known standard.

Roy, certainly you must recognize that the term dBi is not a direct
unit, or measure of field intensity (field strength). The direct,
primary unit of measure of field intensity in accurate, common use is
volts/meter (V/m).

The term dBi is only a measure of the relative gain of a particular
radiator in particular directions stated in decibels with respect to
an isotropic radiator.

Other things equal, the field intensity at a given location is
determined by the gain of a transmit antenna system along paths
serving that location ALONG WITH the matched, r-f power applied to the
feedpoint of that antenna.

The gain of a transmit antenna system in dBi includes nothing about
the absolute amount of power it radiates in various directions.
Therefore by itself, antenna gain(s) in dBi cannot define the absolute
field intensity in standard units/sub-units of V/m that such an
antenna can produce at a given location.

Ergo "dBi" is not a measure of absolute field intensity (field
strength).

RF