Roy, W7EL wrote:
"There are only two ways to change the free space gain of an
antenna---change the efficiency , or change the pattern."

I agree. Terman defines "directive gain" and "power gain" which involve
the pattern and efficiency of an antenna.

The isotropic antenna is by definition omnidirectional. All others are
more directional and thus have gain in their best direction.

The power ratio of a 1/2-wave resonant conductor radiates in its best
direction 1.64 times the power per unit area from an isotropic antenna.
This is a simple power ratio, not dB. This is from Terman`s Table 23-1
in his 1955 edition.

My original posting in this thread was based on the fact that antenna
voltage distribution depends on constructon and frequency. Voltage
amplitudes at all points on the sntenna increase when the rms voltage at
any point rises.. Radiation and reception from an antenna are a function
of antenna voltage. This is unrelated to directive gain.

A higher antenna Q results in higher voltage. The dipole we discussed
was resonant. We`ve seen the textbook curves for resonant circuits which
pften show impedance versus frequency, and we have tuned lumped and
distributed versions. A high Q series resonant circuit has little
resistance to limit current at resonance. A high Q parallel resonant
circuit has little conductance to limit voltage.
My posting said: "Reducing antenna Q by fattening the antenna, reduces
the antenna potential by about the same factor."

A higher Q antenna results in more voltage, more radiation, and more
reception. It also has less bandwidth.

I usually read Roy`s postings because they are interesting and I often
learn something from them. They are greatly appreciated by me and many
others have said they appreciate them too. Some aren`t even EZNEC users,
so there is still room for growth.

On the issue of antenna Q, I recall a Yagi design article which advised
against large diameter parasitic elements as they would have
insufficient Q and not perform properly. That seemed strange to me at
the time but maybe there was something to it.

Best regards, Richard Harrison, KB5WZI