atv transponder on a balloon

[on4bhm]

Hi group,

Would there be any intrest on releasing a hellium balloon into the stratosphere with an atv transponder.
I was thinking on 13 cm input and 6cm output (= into our repeater on0snw input)
so everybody could check on the streaming of batc if he get's over the transponder. (via on0snw streaming to batc)

Any remarks, pitfalls i should think about?

kind regards
73's
on4bhm
sysop of on0snw

[M0DTS]

Interesting idea, lucky you have privileges to do that

I would certainly be up for trying to access when it gets high enough up so the antennas need some signal towards the horizon as well as straight down please!

I monitor the PI4VRZ foxhunt balloon each year on the Sunday of IARU ATV Contest it's tx is on 13cm which is a reasonable signal at times for the distance, maybe you can read about their experiences:
http://www.ballonvossenjacht.nl/

The 70cm telemetry is useful for dish alignment too, the Holland balloon only has voice transponder on 145/435 i think to line up on which can be a bit vague, especially if i am trying to point a 1m dish for 5.7GHz!

Good luck with the project

Rob
M0DTS

[on4bhm]

I know the dutch vossenjacht.
i will be watching this year also.
they repeat the transmissions on pi6atv. and we have a link from them via pi6boz.

I was thinking on a linear transponder 70cm -> 2m
i can do it with sdr.... i order a tronger processor to do it.
and also a new sdr rx/tx

i also ordered a dvb-t stick that can tx.

so many tests to do...

how would reception be of a 2mhz dvb-t signal in 70cm band @25km altitude?
with a fec of 1/2

would the picture be constant... or would there be many dop-outs?

73's
on4bhm

[M0DTS]

Interesting idea to choose 70cm...
What power can you run airborne on this band? this willgive you an idea of the link budget required for good signals.

The repeater on 145 from PI4VRZ is very good at 500KM away and probably 70cm too. Normally at 25-35km altitude the 10mW rtty HAB signals are quite strong like 25-30dB over the noise but thats only in 3KHz, in 2MHz it's a different story!

I'm thinking you will need more than 1W ERP from the balloon for 70cm DATV to get more than 10dB signal to noise and there will always be fading with the antenna continuously moving.

Maybe someone else has some better ideas?

Rob
M0DTS

[on4bhm]

i have a pa of 40w for 70cm.
but its heavy.... heavy cooling plate.... maybe i can do with smaller one... temp drops at 20km altitude...
so i should be able to make 4w erp in dvb-t @2mhz

i have absolutely no idea what this experiment would give...

i hope i can get a permit to lift the balloon one day... all is stricktly regulated over here! it must be a science project!

73's
on4bhm

[Phil M0DNY]

Bear in mind that as the air pressure drops at altitude (down to 2% at 25km), you have a lot less convection from the heatsinks, so if anything they may need to be bigger if you're aiming high!

I look forward to seeing how you get on.

Phil M0DNY

[on4bhm]

So if i understand correct:
the density of the air will compensate the lower temperature? or not completely?


i'm more concerned with the power requirements and the capacity of the lipo's i will need => more weight => more hellium => bigger balloon => more expensive....

i will upload picture of smallest atv repeater ever....
2.350Mhz input -> 5750 Mhz output (200mW for the moment) with osd of position and altitude.

[Phil M0DNY]

More helium = more expensive, I know that well!

I don't know how the trade-off works out with temperature and pressure, there's a lot of other factors such as whether the heatsink is exposed, and how much heat you're absorbing from solar radiation.

As you say, the main issue is the power source, I'm just saying you shouldn't reduce the heatsink spec. Energizer Ultimate Lithiums are the batteries recommended by the UKHAS for HAB flights btw, as they have been proven to perform well in the extreme temperatures, and provide a decent power density.

Regards,

Phil M0DNY

[on4bhm]

i was planning on using lipo's
3 times 5000mAh