"Dave Platt" wrote in message
...
If the rubber ducky is measured by itself, it may not show
resonance at the right band of frequencies, however I wonder if
it uses the handheld case as part of the system, in which case
measurements might change to the anticipated range.

Just a wild guess.

That matches my own experience and experiments. An HT rubber duck
tends to use the HT case, and (via capacitive coupling) the user's
hand and body, as the "counterpoise". If you hook it to the end of a
coax cable, or directly to a service monitor's test output, the
"counterpoise" impedance will be rather different.

Also, the HT duck is often operating in fairly close proximity to
the head, with some amount of loading from that proximity affecting
its feedpoint impedance.

I've tested out a number of "ducks" by attaching them to an MFJ 256 or
269 antenna analyzer. They tend to shift apparent SWR quite a bit
depending on whether I'm holding the analyzer or not, and (if I am)
whether it's out in free space, or held near to my head as if on an HT
in use.

My impression is that most HTs have to be designed to tolerate a
rather lousy SWR on the antenna port... because it often *is* lousy.
Having an HT which burns up its final if you hold the radio wrong
would tend to cause the warranty-repair department to start raising
hell.



I have played with some mobile antennas and mag mounts for 144 to 450 MHz
and found the place it is mounted makes a lot of difference. That is why I
wanted the person to describe how he is checking out the antennas to see if
I could duplicat his results.

Just as bending the ground plane elements of a simple 1/4 wave antenna can
change the impedance a lot, I am sure many things will affect the HT
antennas. Many vertical antennas ar designed to work with a ground plane in
some way, especially the short ones. Not much of a ground plane with the HT
so the hand/arm and most anything else around the HT will probably have a
large effect.

I would hope most HTs are designed to handle wide ranges of impedances
without burning up or creating voltage spikes on the final transistor or
module. I know some specs on RF power transistors state they can handle
very large ammounts of SWR.