[Space] Debriefing Notes

Greg Stramback grog at piratelabs.com
Wed Feb 10 18:13:25 PST 2010


If you mount the antenna vertically, on the TOP of the payload, your
radiation angle is going to be going upward, away from the ground.  At such
a low power, you'll have problem hearing things.

Also, I didn't see the payload... is it a metal enclosure?  Antennas don't
work very well without a groundplane (unless they're specifically designed
for use without one).

My suggestion: mount the antenna facing downward on the bottom of the
payload.  Polarization stays at vertical, ground plane ensures radiation
angle is downward.  Also, switch to a cheap 19" quarter-wavelength antenna
that costs about $5-10.  That way when it gets destroyed from landing...

If you put two antennas on the rig, you'd need to use different impedance
cable... around 90+ ohms to match them properly.  Better to just stick with
one.

-g-



On Wed, Feb 10, 2010 at 5:51 PM, Mikolaj Habryn <dichro at rcpt.to> 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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