Reg,
Thanks for the feedback. I really appreciate it! If I could, I had a
few additional questions regarding some of your points:


Reg Edwards wrote:

Secondly, the antenna pure input resistance changes from its optimum
(designed for) value to an entirely different impedance of resistance
+
reactance.

With the rubber-duck the antenna will be matched to the receiver
input. But
with a different antenna impedance there will be a considerable
mismatch
loss and receiver sensitivity will also be reduced.

Ideally, if the antenna is changed then both Tx and Rx impedance
matching
arrangements should be changed. Which you can't do!

The antenna I had in mind was made for Radio Shack handheld scanners,
and I have a Uniden handheld, which both have a 50 Ohm impedence I
believe... this would eliminate the impedance mismatch, wouldn't it?

The most likely result is that you will hardly notice any difference.
At
best, if you could measure it, you can expect a few dB improvement.
Depends
on how big is the rubber-duck you begin with. Don't throw it away.
You may
wish you hadn't.

The antenna it came with is about 6" long, and I assume it's made to be
a decent antenna for all frequencies the scanner is designed for (29MHz
to 900+Mhz). Just FYI, in case that changes anything...?

Orientation (polarisation) of the antenna relative to balloon antenna
orientation can also make a great difference.

That would be great if I could control the orientation of the
transmitting antenna. It can vary +/- 45 degrees or so during the
flight... the transmitting antenna is an inverted standard 2m handheld
antenna (8" or 9" long?). I've assumed in the past that if I held the
recieve antenna vertical, that's about as good as I can get...?

What does your "Reception is not too great at times" mean.

On the way down mainly, when it's decending between 30 and 100 mph.
I'm assuming this is due to antenna swing.

To effect a noticeable improvement, a 4-times increase in power from
the balloon transmitter would be noticeable.

I'd love to, but due to battery capacity and time of operation, .5W is
what I'm trying to stick with.

Thanks again for the insight! I very much appreciate it.

Dave