Wimpie wrote:
El 04-04-14 2:35, escribió:
snip
Yep, but it isn't a GP antenna which by definition has a radiator about
1/4 lambda.
I understand your reasoning, but do a google (image) search on "GPA
antenna" and you we see that many people don't follow your convention.
5/8 and 1/2 WL are also included. It is not the name, but the
operating princple that is of importance.
Sorry, I follow what engineering text books say, not what some Google
search algorithm comes up with.
snip
You will have common mode currents of some magnitude with ANY GP type
antenna.
Clear, but by using a half wave radiator (end-fed) CM current is about
13 dB lower to start with, and that saves me a lot of aluminum that
doesn't contribute to the radiation. Again, I know
design/construction is more elaborate.
Did you include the coax shield in your simulation?
All antennas connected with coax will have a long conductor consisting of
the coax shield running from the radials to about ground.
You will be hard pressed to notice 1 dB difference in a typical amateur
system.
that was the reason I mentioned:
"The effect of sloping angle on zero elevation gain is small, and you
get hardly measurable more gain when they are almost vertical. Sloping
radials have some other advantage: less birds."
The biggest advantage to sloping radials is they move the impedance from
20 Ohms to much closer to 50 Ohms.
I still can't reproduce, or find a reliable reference for your 3.67
dbi for a quarter wave with quarter wave 85 degr sloping radials.
This will make the third time I will say that number is probably the
result of small angles and closely spaced wires, i.e. garbage.
We drifted away somewhat from Irv's posting....
--
Jim Pennino