Tam/WB2TT wrote:
"Antonio Vernucci" wrote in message
...
...............
If you instead put your receiver/antenna in a point where the two waves
have equal amplitude and same phase, your receiver will measure 200
joules/s (i.e. four times the power produced by each wave alone, not just
two times).
.....................
73

Tony I0JX

You know that can't be right, because combining two antennas gives 3 db
gain. For example, if you connect them in series, you will get twice the
voltage, but the impedance also doubles.

If you supply your power to two identical antennas instead of one, each
antenna gets half the power. If there's no mutual coupling between the
antennas (seldom actually true), then each then produces 0.7071 times
the field strength that the original antenna did, because each is
getting half the original power. At the points where the fields from the
two antennas completely reinforce, the sum of the fields is 0.7071 +
0.7071 = 1.4142 times the field produced by the original antenna. This
is a field strength gain of 3 dB compared to the original antenna, and
it's a field strength gain, as Antonio says, of 2 (6 dB) compared to the
field produced by each of the two antennas.

Your comments about impedance and voltage makes me wonder if maybe
you're confusing feedpoint voltage with field strength. If you connect
two antennas in series and supply the same total power as you did with
one, both the current and the voltage of each will be 0.7071 times the
values the single antenna had. Again, though, all this assumes no mutual
coupling between the antennas, which is seldom true.

Roy Lewallen, W7EL