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[aprssig] TransAtlantic Balloon on 28 MHz (signal)

Bob Bruninga bruninga at usna.edu
Thu Feb 23 20:57:57 UTC 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
challenge.

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
more.

Bob, Wb4APR




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