[amsat-bb] Re: [aprssig] TransAtlantic Balloon on 28 MHz (signal)
nss at mwt.net
Fri Feb 24 06:00:45 PST 2012
Line of sight may be in theory 8000 miles, and possible in satellites,
but in this ballooning you will never ever get this because the Earth
gets in the way. You may at best get a line of sight of 400 to 500 miles
at the most.
The Original Rolling Ball Clock
On 2/23/2012 10:38 PM, Roger wrote:
> So...in several weeks you will launch?
> 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
>> 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
>> 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
>> 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
>> Bob, Wb4APR
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