Your tests really do not measure gain perse of the antenna but more
the efficiency of the antennae tested. Now that can be calculated into
a dB ratio and presented as gain. In reality it is not actually the
gain of the antenna.

The db expressed was not intended to be the gain (dbd, or dbi) of the
antenna.

That would reconcile the large variations of
readings between the extremes.

Radiated power(Pr) from a 1/4 antenna is

18.27* Im^2 = Pr

where Im is the magnitude of the antenna current. Gain calulations of
an antenna factor in power loss to heat and other factors(Pl). Thus
the total power into an antenna is the sum of power radiatied as a TEM
wave and those losses which are incurred. While at very small power
levels the heat loss in an antenna does apporach zero. There are other
losses besides heat. The largest of all is ground loss.

Mobile installations can be as poor as 5% efficient. That results in
only 5% of the total power input actually being radiated. A very good
mobile installation can be as good as 65% efficient. In dBs that would
be about 11dB.

Lastly,I beleive that you mentioned that the distance separating the
two antennea were about 200 feet. A better distance would be 350 feet
minimum. This will get you beyond 10 wavelengths separation. In that
distance, near field power is a nonfactor and the TEM wave off the
antenna is fully formed. The near fields from an antenna are
measurable out to about 3 wavelengths from the antenna. It is there
that the TEM wave is nearly formed and by ten wavelengths from the
antenna is its strongest.

Trust me antenna efficiency is far more important than antenna gain in
a mobile installation. HIgh ground losses, can make the best mobile
antenna look horrible.

james

OK, so in the real world we are never effected by "antenna
efficiency", "ground loss" ect.ect.?

The test is as stated. It was never intended to be a lab test. It
was intended to show what would happen if this particular test
scenario was followed.

On Tue, 31 Jan 2006 16:01:52 -0500, wrote:

+OK, so in the real world we are never effected by "antenna
+efficiency", "ground loss" ect.ect.?
+
+The test is as stated. It was never intended to be a lab test. It
+was intended to show what would happen if this particular test
+scenario was followed.
*****

In the real world ground losses in a mobile installation are real and
can be quite large. These losses affect efficiency and thus
performance.

What you did is to show that there can be marked differences between
antennae and their istallation. The more complex issue is, are these
same differences repeatable from vehicle to vehicle and area to area?
I seriously doubt that they are.

james