[chbot] Sundays balloon-adventure, report please

[André Geldenhuis]

On Tue, Jan 8, 2013 at 12:48 PM, Mark Atherton <markaren1 at xtra.co.nz> wrote:

> Hi Andre,
>
> 4 baud / 10mW / 433MHz sounds like a superb mix to me.
>
> +10dBm TX, with a 150km clear path gives an RX level around -130dBm.
>
> You should be able to get 20dB processing gain (due to the very narrow
> bandwidth) over a regular NBFM signal (with nominal RX threshold of
> -120dBm), so all these numbers seem to stack up well at first glance.
>
> If you want to borrow a 5 ele 430MHz Yagi, I have a commercial one kicking
> around. That should add 10dB over a whip on a handheld (if that is what you
> were using).
>
> Yeah we were using a five element yagi, basically one of these<http://www.google.co.nz/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&ved=0CGEQFjAG&url=http%3A%2F%2Fwww.amsat.org%2Famsat-new%2Finformation%2Ffaqs%2Fcrow%2FJulAug06AmsatJournal.pdf&ei=2vLrUKqkI8qamQWhl4GIDg&usg=AFQjCNECFW3bIiqjq4eEQA66zhBdVajxhw&sig2=Xd6tAubbzDFfsHhNQiVBrQ>.
Not sure how well they perform compared to a proper tuned one.


> I also have a 430Mhz helical filter you can borrow which should do a half
> reasonable job of keeping adjacent channel cr*p out of the front end.
>

Awesome, that could definitely be good to have a  look at borrowing
sometime, much obliged.


> Please post more details about the modulator, transmitter etc.
>

The transmitter was one of
these<http://nz.element14.com/quasar/qam-tx1/module-transmitter-am-433mhz/dp/1304024>.
We used direct digital synthesis on an arm STF103ret6 driving one of the
12bit DACs.  The encoding was DomnioEX4 which I based on the fldigi
implementation.  The antenna on the balloon was just a 1/4 wavelength wire
dangling out the bottom of the payload.


> PS any photos from the launch site ?
>
> Hanna did a bit of a write up here <http://team9point99.blogspot.co.nz/>

Cheers
Andre
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