[chbot] Sundays balloon-adventure, report please

[Mark Atherton]

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).

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.

Please post more details about the modulator, transmitter etc.

Thanks,

Mark

PS any photos from the launch site ?



At 09:48 a.m. 8/01/2013, you wrote:
>Hi Chris
>
>Sounds like a cool project :)  The reason we 
>went with 10mW was that the transmitter costs 
>about $5 and weighs about 1 gram.  Our entire 
>payload including 2 cameras, spot tracker, 
>electronics, batteries for 5hours + and 
>insulation etc only came to 900 grams and I 
>reckon we can reduce the weight some more.  10mW 
>also saves on battery weight.  We also don't 
>really need a faster data rate unless we want to 
>transmit video, which we have considered 
>doing.  Obviously our 4 baud data rate wouldn't be up to that :P
>
>Cheers :)
>Andre
>
>On Tue, Jan 8, 2013 at 8:08 AM, Chris Hellyar 
><<mailto:chris at trash.co.nz>chris at trash.co.nz> wrote:
>Hi Andre,
>
>Can I ask a possibly not relevant question: why only 10mW?
>
>There is unlicensed spectrum in the PRS band for 
>telemetry, or you could get a ham involved and 
>run licensed in the 70cm band (Although not that 
>frequency, that's in the repeater uplink section 
>of the band) .  Both options would let you run a higher bandwidth downlink.
>
>Just curious about the design decision as a 
>rapid ascent balloon is one of my (many) unfinished projects.
>
>I made the payload container a couple of years 
>ago and got as far as making the camera 
>controller and researching GPS's. My cunning 
>plan was to launch to time the burst with an ISS 
>overhead pass and relay telemetry off the APRS 
>digipeater on board.  It was my main motivation 
>to getting my amateur license at the time, 
>although now I've got the DX bug and that's a whole other bowl of cornies.
>
>Cheers, Chris H.
>
>
>
>
>On 07/01/13 23:58, André Geldenhuis wrote:
>>Partial success I'm afraid :P
>>
>>The spot tracker stopped above 60k feet which 
>>we expected but I had hoped it would start 
>>working once below that again.  It appears not 
>>for whatever reason.     We also had a 10mW 
>>radio on board the balloon transmitting 
>>location, altitude and temperature which the 
>>recovery team managed to track all the way out 
>>to 80km with good decoding except when the 
>>balloon was low on the horizon.  The last GPS 
>>fix was at 3436m at a composite position of 
>>-44.04174, -173.04946.  The position is 
>>composite as the last two messages only 
>>contained one of latitude and longitude due to 
>>signal breakup.   It puts the payload out to sea south of akaroa harbour.
>>
>>
>>The balloon ascended much slower than 
>>anticipated and we are not sure why yet, we are 
>>still going though the data to try and figure 
>>out what happened.  The slow assent was the 
>>reason the balloon went out to sea, it took 
>>much longer to reach its burst altitude.  Next time we will have cut downs :P
>>
>>We are hoping it washes up and someone finds it 
>>and returns it to us. The electronics will be 
>>wreaked but the two camera SD cards and data 
>>logger SD cards might still be ok and it would be nice to see the pictures :)
>>
>>We got about 80% of the objectives for the 
>>flight though and we planned to iterate all the 
>>electronics and replace the spot with a spot 2 
>>which has a ublox GPS unit so will work above 
>>60k feet.   We will fly the next iteration soonish.
>>
>>
>>I'll let the list know if we get any picures back
>>
>>Cheers
>>Andre
>>
>>
>>On Mon, Jan 7, 2013 at 8:51 PM, Mark Atherton 
>><<mailto:markaren1 at xtra.co.nz>markaren1 at xtra.co.nz> wrote:
>>Hi Andre,
>>
>>Looks like it was a sucess, well done.
>>
>> From <http://goo.gl/1o6o6>http://goo.gl/1o6o6 password microprize ...
>>
>>Launch time close to 10:42, with signal loss 
>>12:51, so just over 2 hrs flight time (?)
>>
>>Not obvious what altitude you managed, or I 
>>haven't found the correct button yet.
>>
>>Any chance of a quick report here and maybe a 
>>fuller report with photos at the next Tait-meeting ?
>>
>>Regards,
>>
>>Mark