[Space] Debriefing Notes

nils at shkoo.com nils at shkoo.com
Thu Feb 11 02:19:32 UTC 2010

The digipeaters on the mountains will repeat via RF when they hear a 
packet, assuming your path is set right.  As long as you have a decent 
antenna on your receiver, you should pick those up fine, even if you're 
directly underneath the balloon.  At least in theory. :)

On aprs.fi there are some info on some of the nearby repeaters and their 
power output:


Also, I really recommend getting an external antenna to receive as well. 
Anecdotially, it makes a big difference for me when I'm using my HT. 
Just hanging out I generally manage to receive a beacon every couple 
minutes with the builtin duck antenna, but several a minute with the 
external antenna.  It's even more of a difference when I'm in a big metal 
box like my car.

If we want to get really fancy we could set up a mobile digipeater with a 
directional antenna (like a Yagi or something) to receive, keep it located 
somewhat away from the balloon, and point the Yagi at the last beaconed 
location. :)


On Wed, 10 Feb 2010, Mikolaj Habryn wrote:

> It's so obvious when you explain it :) This probably does explain all
> of our APRS problems. So if we want to talk to both distant
> digipeaters and to chase crews (who are aiming to be directly
> underneath), what's the best thing to do? Dual antennas?
> m.
> On Wed, Feb 10, 2010 at 4:57 PM,  <nils at shkoo.com> wrote:
>> Here are my thoughts on the APRS problems:
>> It sounds like the transmit antenna was mounted horozontally.  This would
>> make it very difficult for the digipeaters to pick up the signal, since
>> most everything uses vertical polarization.  The difference in signal is
>> on the order of tens of dB (reference
>> http://en.wikipedia.org/wiki/Antenna_%28radio%29#Polarization).
>> Also with a horozontal antenna, you would only be broadcasting to a strip
>> on the ground, and half the transmission is sent off into space.  With a
>> vertical antenna you send the signal in all (horozontal) direcitons.
>> Also, the APRS packet takes about a second to transmit.  If the payload is
>> rotating rapidly during that time, the coverage area of the transmitter
>> will change so it'll be less likely any one digipeater will see the whole
>> packet.
>> -nils
>> On Tue, 9 Feb 2010, Andrew Gerrand wrote:
>>> What was done well:
>>> - SMS messages
>>> - Data logger
>>> - Balloon fill (the fitting was the key)
>>> - Retrieval
>>> - Good launch site
>>> What went wrong:
>>> - Overfilled balloon
>>> - Didn't measure the pull
>>> - If we'd had three points of connection, 2-3 metres long, to the
>>> payload we would have had less or no swing
>>> - Android GPS bugs
>>> - Stressing the balloon through the angle of the fill (not having a hose)
>>> - APRS LI batteries got too cold
>>> - APRS system too immature - didn't play with it enough
>>> - Water condensation caused problems
>>> What we need to do:
>>> - Figure out how to calculate how much helium to put in a balloon to
>>> take it to height X
>>> - Maybe get a better balloon? We need more lift
>>> There was more but it got a bit rambly and I tuned out for parts =)
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