[amsat-bb] Re: [aprssig] TransAtlantic Balloon on 28 MHz (signal)

[Roger]

So...in several weeks you will launch?

Roger
WA1KAT

On 2/23/2012 3:57 PM, Bob Bruninga wrote:
>> 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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