[amsat-bb] Re: [aprssig] TransAtlantic Balloon on 28 MHz (signal)
bruninga at usna.edu
Thu Feb 23 12:57:57 PST 2012
> We are working on a 28 MHz transatlantic Balloon with a
> CW transmitter on 10m using (of course) a vertical dipole.
> Do you have a 10 meter (28 MHz) vertically polarized beam?
The response was as expected. No one has. Therefore we will accept
horizontal beam headings. Also we will ask for signal strength reports
including a reference signal level with and without antenna.
We just did a far-field test line-of-sight over 0.88 miles and had a 75 dB
Signal margin (vertical to vertical). This is above about 21 dB of antenna
noise. This implies about a line-of-sight range of over 8000 km. So it
looks like signal strength should be no problem...
The FT-817 S meter was tested to reveal a ridiculous range of from 1 to 20
dB per S unit. The range comparison is not much better as shown here...
-43 dBm S+++= .25 km
-55 dBm S++ = 0.4 km
-63 dBm S+ = 2.5 km
-73 dBm S9 = 8 km At altitude even overhead
-93 dBm S8 = 82 km
-97 dBm S7 = 100 km
-98 dBm S6 = 115 km
-99 dBm S5 = 130 km
-100 dBm S4 = 184 km
-101 dBm S3 = 206 km
-102 dBm S2 = 231 km
-103 dBm S1 = 258 km
Min signal = 8000 km
So hearing it won't be a problem, but guessing where it is will be a
We are currently waiting on the Helium and the balloons. Total mass is about
double the weight of a 9v battery.
Launch probably a few weeks away yet. Oh, and Hydrogen (H2) which is 50%
lighter than Helium only gains about 5%. The way to think about it is not
to compare He to H2 (2-to-1) but to compare Air-to-Helium (10-to-1) and
air-to-H2 (10-to.5) so the difference in lifting capacity is only 0.5 out of
10 or about 5%. Now it makes sense.
The real advantage of H2 is you can make your own. He is a limited natural
resource that we are running out of even faster than we are running out of
dead dinosaurs. And it takes millions of years of radioactive decay to make
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