[Elecraft] dBd vs dBi

[k6se@juno.com]

Logan, KZ6O wrote:

"You need to be a little careful of the Force 12 numbers.  What they mean
is that they have taken into account the effect of ground reflections. 
Notice the phrase  "compared to a full sized dipole at same height".
==========
Although I prefer "dBi" and and I prefer "free space" if "dBd" is used,
Force 12's use of "dBd" over real ground is still quite fair.

For example, a 40-meter dipole in free space has a gain of 2.14 dBi.  A
2-el 40-meter Yagi in free space might have 6.45 dBi (4.31 dB more than
the dipole).

Putting those same two antennas 75' over real ground with "average" soil
conductivity yields 7.92 dBi gain for the dipole and 11.46 dBi gain for
the Yagi.  Here the Yagi is only 3.54 dB better than the dipole !!

Therefore, Force 12's choice to to "dBd over real ground" is on the
conservative side!

On the other hand, nobody has *ever* been able to get 8.81 dBi gain out
of a 3-element Yagi, as SteppIR claims (about 8.2 dBi is the max
possible).

73, de Earl, K6SE