Building Remote Sensor for Scientific Researchers

Hi there,

I’m helping a research scientist build a remote sensing device to protect forests from illegal logging. I’m new to SDR and would like to have some advisors I can bounce questions off of. If anyone is willing to field inquiries related to SDR and satellite comm options, please drop me a line!

I’m looking at Outernet as an option due to its low price point. I’m waiting to find out if the Twitter integration still exists so that we can get data from the field. Any guidance on that method or other ways of receiving very small data packets back from the device is welcome.

Thanks, all!

Matthew Epler
http://mepler.com

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I’m not sure about the startup costs for such an endeavor, but here are the prices to use such a satellite:

https://satellitephonestore.com/inmarsat/service/bgan

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Thanks for the link! If the Twitter service does still exist for Othernet, am I correct in thinking this could be used to get simple data back? Here’s the thread where it’s mentioned: Is line of sight that important?

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@matthew_epler the Twitter integration was for broadcasting tweets. We are working on a return channel, but it won’t be ready until next year.

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@Syed thanks for the reply. Still a little confused. I can broadcast a tweet from anywhere using the Dreamcatcher hardware - correct?

If so, I can monitor the twitter account for any changes and it’s effectively a packet delivery system. Am I right?

Thanks again,

M

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No, you can receive a tweet anywhere using the Dreamcatcher hardware (and the Outernet satellite service)

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Ah, thanks. That clarifies it.

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check this: https://www.sparkfun.com/products/13745

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now thats Freaking Cool…
Bookmarked that!!!

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I’ll second that!

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@Syed it will me amazing once you get the return channel working

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@zoltan thanks for the link. I had seen that and their website said you need a clear view of the sky for it to work. To verify, I’ve scheduled a phone call with their support team this morning. I’ll report back here.

UDPATE: notes from call with Rock7:

  • Iridium’s Short Burst Delivery is perfect for small packets sent sporadically.
  • Satellites (66 total) travel North-South.
  • Retries if not sent. (Frequency of retries will affect battery power)
  • Do not rely on signal strength returned by unit via AT command. While accurate, it only happens every 20 seconds so it will have changed by the time you read it and do something about it. Instead, just try to send and if it doesn’t go through, retry.
  • Patch vs. Helical
  • Patch has ground plane. Larger = better. Eliminates interfernce better than helical. Has a half-dome reception pattern.
  • Helical has radial reception pattern and better for orientations that are not fixed or need a wider view of sky. Recommended for our purposes due to flexibility of orientation when mounting.
  • All of their boards can be ordered with SMA connectors for antenna
  • 9602 vs. 9603. Both the same functionality and price. 9603 is smaller/lighter and has smaller/more finicky headers. Both 5V, UART, no microcontroller or logic - just the AT commands and responses.
  • RockBlock + is waterproof unit, runs on 9-30V and uses RS232. Ideal for longer-cable situations.
  • When building housing, avoid metal, carbon fiber, and fire-retardant plastics (due to high carbon content). Also, if using a patch antenna, leave at least 5mm distance between antenna and case walls.
  • Supercapacitor on the board is for storing energy needed in bursts for transmission. In sleep mode, this still draws power. Some people add a FET transistor inline with the cap so that it is completely shut off during sleep.

Since this forum is dedicated to OUTERNET and related projects, I’ll stop posting anything related to competitor projects but will continue to discuss general concepts like antenna design, etc. for anyone interested. Just wanted to follow through on the info for anyone else like me looking for a 2-way solution.

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Actually since we are a bit off topic already, there is actually no good reason other than finance why Outernet can’t also buy and then offer some uplink bandwidth on the same satellites it is broadcast by.(sadly RockBlock interfaces with Iridium satellites not Inmarsat) I agree that it would be a new expense and perhaps diversionary, but a limited uplink on a band that we can get some easy hardware for would be a massive value add to sume of us living remotely in war torn areas which would draw subscriptions or credit purchases like the old twitter feed especially if you took BTC in cases where our local currency is embargoed. Maybe there are less hacker geeks than I imagine but there is already a place for the backcountry satellite messenger devices, perhaps Outernet could hang off of that added service fo use in wealthier countries as a sort of buy one shere one deal like OLPC but use the existing goodwill from humanitarian connections to make Outernet the low bandwidth short message uplink of choice for Red Cross/Crescent, Médecins Sans Frontières, and others.

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A return channel (transmit) is always something we think about. I’ve looked into it in detail. It’s a financial problem more than a technical one. The problem is paying for bandwidth. Most of the organizations that have a real need for a messaging service would have no problem paying for Iridium or Spot Messenger (Global Star).

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For a return channel how much bandwidth is needed if it is limited to at first some very narrow PSK/FSK, even CW; the types of uplink seen on bent-pipe transponder amateur satellites would be fine depending on what the Inmarsat will accept from analog. Even allowing one SMS a week, perhaps more if requested/purchased for an emergency would be pretty cheap especially if pooled and on a subscription model. It would likely only take a sliver of frequency especially if there is a automated side channel protocol for requesting permission/time and receive acknowledgement to be transmitted on the downlink. During a test period concerns of jamming might be discounted though they would eventually need to be addressed in the protocol and not just in obscure hardware, I suggest spread spectrum/freq hopping. Best of all uplink could still be done with hacked hardware like FM walkie-talkies or the emerging pool of SDR-TX options like hackRF and a TX amp if they used a good yaggi antenna(assuming that the Inmarsat galaxy does sub GHz UHF), even better if it were frequency shifted up to microwave freqs for nice small but tricker to build DIY antennas and circuits.
Considering what people are willing to pay for similar service I think both hardware and bandwidth would both help keep the org afloat, encourage some sweet and possibly pioneering cheap hacking both in the first and third world while also enabling/financing the primary education and econ dev missions. COnsider what is already happening with Brazilian pirating bandwith off of the US Navy’s FLTSATCOM, now begin to make it a legal and viable communication asset for humanity.

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I’ve got a RockBLOCK and highly recommend it. Did some work on interfacing with it here. It works great. The service is reliable and their API/portal is very straightforward to implement. If your application can justify the $13/mo/device + ~$0.10/message cost, then it should work great. I tested mine on the dashboard of a small aircraft and it did not have any issues.

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I’ve not used a RockBLOCK, but I’ve only heard good things about it. It would be ideal if the modem price could get under $100. The monthly and per message price is not unreasonable, considering that it has full global coverage.

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the biggest problem when you want to scale a return link for thousands of users is the collision I guess… GEO satellites are not too practical as millions of users can see a single satellite…

perhaps with clever techniques like synchronous network (maybe GPS based) it can utilized for avoid collision

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Zoltan, the problem has been solved various ways over the decades. But at first with DIY equipment a low bandwith experimenters club approach would work until there is an easy rockblock equivalent module made and then likely a real packaged solution available. The reality is I doubt even amateur radio licensees could get a waiver permit to use DIY TX gear for Inmarsat comms, we will have to use established hardware but it is out there, just not as easy to access right now as iridium stuff.

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Yeah, RF HW is very important to avoid interference with other sats radiation pattern of the antenna, antenna, pointing, hamironcs, output power all should have tuned and set precisely…

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