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.