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Julianfer5

Battery had to be disconnected during launch. Two microswitches connected the battery when it was ejected out of the launch tube. It started transmitting immediatly.

I also did the software for a beacon that was launched from the ISS a few months back, that had to wait for two days before starting transmitting.
That is a great idea haha, so simple yet so effective, Damn amazing stuff man!. Last question hahaha, Is active attitude control worth it on a pocketqube? Can you use everyday neodymium magnets for passive control? Thanks!

srnet

That is a great idea haha, so simple yet so effective. Last question hahaha, Is active attitude control worth it on a pocketqube? Can you use everyday neodymium magnets for passive control?
Active control would be hard, remember the power constraints caused by the low surface area available for solar panels. The more stuff you add ther more there is to go wrong.

We used a single neodymium magnet which worked well. In retrospect it should have been at a different angle so that the solar panels spent more time fully pointing at the sun. A second magnet, also realised in retrospect, would probably have stopepd it spinning along its long axis. The spinning caused the FSK RTTY to fade in and out a bit.

Its easy to dismiss the FSK RTTY we used as old tech, but it was the main reason for the projects sucess. The advantage was that virtually every radio amateur in the World listening on 434mhz had the gear to pick up the basic telemetry. As a result we had a great many reception reports from all corners of the World. Even at 2000km+ I was able to pick up the data sent at 100mW using a simple omni antenna.

I did write Arduino FSK RTTY software for the LoRa devices.

$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Julianfer5

Active control would be hard, remember the power constraints caused by the low surface area available for solar panels. The more stuff you add ther more there is to go wrong.

We used a single neodymium magnet which worked well. In retrospect it should have been at a different angle so that the solar panels spent more time fully pointing at the sun. A second magnet, also realised in retrospect, would probably have stopepd it spinning along its long axis. The spinning caused the FSK RTTY to fade in and out a bit.

Its easy to dismiss the FSK RTTY we used as old tech, but it was the main reason for the projects sucess. The advantage was that virtually every radio amateur in the World listening on 434mhz had the gear to pick up the basic telemetry. As a result we had a great many reception reports from all corners of the World. Even at 2000km+ I was able to pick up the data sent at 100mW using a simple omni antenna.

I did write Arduino FSK RTTY software for the LoRa devices.


Yeah I was thinking indeed attitude control would be too demanding for the power capabilities of a picosatellite that size, I am actually contemplating the idea of possibly keeping the voice synthesizer meaning anyone can tune in without decoding, maybe some sort of alternation between coded audio and synthesized voice. Did you take any action to counteract the doppler effect?

Thank you so much man!


srnet

I am actually contemplating the idea of possibly keeping the voice synthesizer meaning anyone can tune in without decoding, maybe some sort of alternation between coded audio and synthesized voice.
Voice ?

You sure, have you actually tested that you will have enough link margin that it will be heard ?


Quote
Did you take any action to counteract the doppler effect?
It would in theory be possible to adjust the frequency of transmissions to compensate for ground reception, but it could only be done for one particular point on the globe, or if you had two way comms with the satellite to instigate the 'compensation' when required. 

But to answer the question then no, we did not take any action to compensate for doppler, basically because its not really possible in such simple systems. I did (extensivly) test that the ground based recievers could cope with the known frequency shifts due to doppler.

$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Julianfer5

Voice ?

You sure, have you actually tested that you will have enough link margin that it will be heard ?


It would in theory be possible to adjust the frequency of transmissions to compensate for ground reception, but it could only be done for one particular point on the globe, or if you had two way comms with the satellite to instigate the 'compensation' when required. 

But to answer the question then no, we did not take any action to compensate for doppler, basically because its not really possible in such simple systems. I did (extensivly) test that the ground based recievers could cope with the known frequency shifts due to doppler.


I have not tested anything yet but will start testing soon hopefully, voice could be an interesting addition to the amateur ham community even though RTTY decoding is dead easy with an SDR nowadays. Yeah I thought doppler effect would be hard to counteract at such a basic RTTY transmission it would not have much effect.

Anyways I'll start experimenting with a couple LoRa radios I have ordered and will keep you updated, But pretty much its a basic PocketQube possibly acting as a mothership to launch the smaller picosatellites.

Thanks Man your help is really helpful and the work you did and are doing is amazing!


Cheers,
Julian

srnet

#20
Jun 20, 2018, 08:12 am Last Edit: Jun 20, 2018, 08:16 am by srnet
It all comes down to numbers.

You need to know how much power you have available, how much current and for how long.

Is it battery only (wont last long) or solar as well.

With those numbers you can work out how much transmit power you can use.

Then and only then you can postulate which transmission methods you can use.


There is a Video at the link below of a talk I did which explains the project in some detail, there is also a bit at the end on some of the early long distance research I did on LoRa;

https://www.youtube.com/watch?v=q00Fm-ij02M
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Julianfer5

#21
Jun 20, 2018, 02:30 pm Last Edit: Jun 20, 2018, 02:37 pm by Julianfer5
It all comes down to numbers.

You need to know how much power you have available, how much current and for how long.

Is it battery only (wont last long) or solar as well.

With those numbers you can work out how much transmit power you can use.

Then and only then you can postulate which transmission methods you can use.


There is a Video at the link below of a talk I did which explains the project in some detail, there is also a bit at the end on some of the early long distance research I did on LoRa;

https://www.youtube.com/watch?v=q00Fm-ij02M

Great talk haha!
So much stuff to think about when building the satellite!

Im still working on the power system since that is the basis of the whole satellite but I am just having trouble with finding GaAs solar panels since the system depends on that, just curious what provider did you use to get the cost down to 125 Pounds!!?? Also, I'm currently based in Spain so do FCC regulations apply (since they don't seem to like picosatellites due to their difficulty being tracked)?

Thanks

srnet

We used TASC solar cells, state of the art at the time, circa 28% efficiency;

http://www.spectrolab.com/DataSheets/PV/PV_NM_TASC_ITJ.pdf

At the time they were around $3 each, we used 24, but they may be $5 these days, they did become popular.

$50SAT cost £125 in parts to build, dont think I ever said that included the launch, which we did not pay for.

FCC or even CE stuff does not apply for satellites launched as an Amateur radio satellite.

It was not known at the time of launch if indeed a 200g satellite could be tracked by Norad, but we were able to do quite an accurate direction find on its transmitter and that matched to within 2 seconds of the postion in the sky predicted by the Norad tracking radar.   
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

srnet

You might want to take a look at my high altitude balloon tracker software, it uses an Atmega 328 and a LoRa device, it was also designed to have much of the basic communication setup that you need in a small satellite, it sends LoRa and\or FSK RTTY.

With small satellites (and small balloon trackers) you probably do not have the power available to run the receiver 100% of the time. So for the remote control you need, get the tracker\satellite to wake up from power saving sleep, say once a minute. The tracker\satellite sends a 'clear to send packet'. The ground based receiver has been told to send a command to do something (send a test message for instance), so its waiting to receive the 'clear to send packet', when it does it sends the command and waits for an acknowledge. It will retry the command send if it gets no reply.


HAB2 Tracker Software
$50SAT is now Silent (but probably still running)
http://www.50dollarsat.info/
http://www.loratracker.uk/

Julianfer5

We used TASC solar cells, state of the art at the time, circa 28% efficiency;

http://www.spectrolab.com/DataSheets/PV/PV_NM_TASC_ITJ.pdf

At the time they were around $3 each, we used 24, but they may be $5 these days, they did become popular.

$50SAT cost £125 in parts to build, dont think I ever said that included the launch, which we did not pay for.

FCC or even CE stuff does not apply for satellites launched as an Amateur radio satellite.

It was not known at the time of launch if indeed a 200g satellite could be tracked by Norad, but we were able to do quite an accurate direction find on its transmitter and that matched to within 2 seconds of the postion in the sky predicted by the Norad tracking radar.   
Ah ok, so there is no limit on how small they can be, interesting. I contacted spectrolabs a while back but still not reply...


You might want to take a look at my high altitude balloon tracker software, it uses an Atmega 328 and a LoRa device, it was also designed to have much of the basic communication setup that you need in a small satellite, it sends LoRa and\or FSK RTTY.

With small satellites (and small balloon trackers) you probably do not have the power available to run the receiver 100% of the time. So for the remote control you need, get the tracker\satellite to wake up from power saving sleep, say once a minute. The tracker\satellite sends a 'clear to send packet'. The ground based receiver has been told to send a command to do something (send a test message for instance), so its waiting to receive the 'clear to send packet', when it does it sends the command and waits for an acknowledge. It will retry the command send if it gets no reply.


HAB2 Tracker Software

Yeah I just noticed it on the talk, bummer but makes absolute sense, Another problem I have is I dont own an amateur radio license in my country so I'd need to find someone if I hypothetically ever continued with this and needed to send data. I'll take a look at the project but LoRa seems like the perfect radio architecture for this project, Amazing work man!

Thanks!

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