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

On 31 Jul 2006 09:59:54 -0700, wrote:
http://www.coronaos.com/hg908y.pdf
http://www.coronaos.com/hg908p.pdf

Hi Brett,

These are commercial antennas, the first is what you might use in your
chase car. It exhibits gain from the complexity of its design. It
also exhibits a sharp lobe that is inconsistent with use on a balloon
(unless you add tracking servos - yeh, you are not going there).

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.

If you have such a tight weight budget, you should be doing it
yourself. Packaged products are always heavier. You "could" get away
with a simple piano wire stinger stuck into the transmitter's jack.

73's
Richard Clark, KB7QHC

wrote:

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.

REDACTED

YEP! Three hundred miles away IF ... IF the balloon is at 100,000 feet
altitude!! The specs read "line of sight".

At an altitude of 10,000 feet the radio line of sight horizon is about 120 miles.

A typical UHF [900 MHz] receiver should be able to receive a signal as weak as
0.0000000000002 [2E-14] watts [1 uV] using a simple vertical antenna. Three
hundred miles line of sight from 100,000 feet altitude is approximately 1.4E6
wavelengths. The power density at 300 miles from a 100,000 feet high balloon is
approximately 8E-14 watts/wavelength^2 [2 uV]. The signal should be heard, but
the noise margin is low for reliable digital data transmission. A gain antenna
at the receiver will improve the signal to noise ratio significantly.

The forces at work here are simply the receiving sensitivity of your earth bound
receiver. Ham receivers have sensitivities less than 1 uV.

The power divergence from the transmitter was assumed spherical for 1.4E6
wavelengths, and the receiver was assumed to have 1 uV sensitivity.



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.

Above is for the balloon. Below is for the chase vehicle.




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


REDACTED

Either antenna should do the job. The hg908Y would let you eyeball sight along
the axis in the general direction of the balloon. Both are gain antennas.