wrote:
Thanks, everyone. But you guys still made things complicated.

No, they didn't. Antennas themselves are complicated. Formulas exist only
for specific well-defined environments, none of which fits your
configuration close enough to be meaningful.

I said it
is just wire antenna, only for a very small output power, 10mW.

Output power has nothing to do with antenna impedance.

In
order to eliminate the confusion or misunderstanding, let me put some
pictures to illustrate:

(1) This transmitter, 10mW, at 450MHz, wire length(lambda/4 for
450MHz)=16cm. What is the wire antenna's impedance?
http://www.charto.info/antq1.jpg
(2) This transmitter, 10MW, at 450MHz, Rod Extendable Antenna is
extended exactly as 16cm(lambda/4 for 450MHz). What is its antenna's
impedance?
http://www.charto.info/antq2.jpg

Given that such specific conditions are as shown in the pictures, is it
still difficult to tell, even for a rough number within a range such as
50 to 80 ohms, or 500-800 ohms?

Yes, it is. And, whatever number you are given will not necessarily be
correct from one time to another. The impedance will change if you pick up
the radio or the camera. The impedance will change if you change position to
be near another object.

Suppose you are told that the impedance will be 20-j35? What will you do
about it? Since you feel that the expert advice you received simply
complicated the issue, one can only assume that you do not have the
knowledge to cope with an answer.

Go to your local ham club and find somebody with an antenna analyzer. Put a
quarter-wave wire into the connector and wander around while recording the
maximum resistance and reactance. You can see it change all over the place.
No, it doesn't go from zero to infinity. The impedance will be different
from that when the antenna is installed on your actual object.

Here is a number. Do with it what you will.... Z ~ 35-j35. If you don't like
this number, get EZNEC and model your own antenna. Or, get your own analyzer
and measure your wire. Be sure to include hand and body capacitance in your
model. Also be sure to model your tripod, soil conditions, nearby trees, the
object enclosure, etc.

Good luck.

John