Dave wrote:
At an altitude of 100,000 feet 1000 mw [1 watt] should reach to the radio
horizon of about 300 miles assuming a good receiver on the far end of the range.


Do you mean that I should be able to pick up a signal from 300 miles
away??? I don't believe I understand the forces at work here.


A vertically polarized 1/2 wavelength antenna should work fine. At least it
would be my starting point. Second option would be an inverted [upside down] 1/4
wavelength ground plane. Either antenna is not expensive.


I was hoping to only put an antenna on the vehicle that I chase the
balloon with. It weighs too much to put it on the balloon itself.
However, would it decrease my performance that much??? I asked this
similar question to Aerocomm(who manufactures the radios). They sent
me two possible antennas, but I'm not sure either is really what I
want.
http://www.coronaos.com/hg908y.pdf
http://www.coronaos.com/hg908p.pdf


What information is to be transmitted? If you are looking for moderate speed
telemetry then a path loss versus error rate study needs to be done. If data is
being transmitted a gain antenna may be required at the receiver. Gain antennas
are not expensive and the antenna needs to be pointed at and follow the
balloon's flight path.


I'm not really sure how much data is transmitted. You need to check
out the product description for these devices. From a programmer's
perspective, I don't need to do any initializing of the radio.
Whatever data I transmit out of the serial port is what shows up out of
the other radio's serial port. Pretty basic. I am not planning to
send images back, just little bits of data. But I would like the
reliability of the connection to be such that I could send back a photo
if I needed to.

It would be nice if somebody could give me a link to a website where I
could buy the proper antenna with a proper connector.


Here is the e-mail from Aerocomm:

You can try one of the antennas that I have attached information on.
The panel offers better overall coverage while the yagi is more focused
and covers longer distance. These are not officially approved for use
by the FCC. Remember that the ConnexLink has a reverse polarity SMA
jack for the antenna connector.



Thanks for all the replies!
Brett