Long range, low bitrate, small data transceiver unit for telemetry data

Satellite phones :-)

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wireless ap and decent directional dishs

Would a GSM/GPRS cell phone data module work?

See

They work great where ever you have cell phone coverage. The data charges can add up if you have to move a lot of data. The costs are low for low data rate applications. $25/month (Canadian dollars) gives us

256KB/month which means about 8KB/day. The more data you sign up for, the lower the cost per byte. Check with your GSM cell phone provider.

The hardware is reasonable priced and the developer's kit is inexpensive. The dev kit even includes a power supply with power cords for most countries except Australia.

Actually, that raises an interesting question - I know various applications including buoys, wild animal research collars, etc. use a satellite uplink to communicate GPS data and other telemetry to home base.

Who does one contact about buying bytes on a bird like this? I'd be interested to find out what it costs to set up this sort of thing.

A general search on argos satellite applications will yield lots of results.

Mark Borgerson

EXTREMELY interesting, thanks for the link! One transmission a day on a floating platform is about $77 per month, which gives you position data plus 256 bits of telemetry.

There is a clause in there about not being able to get bird time if there is a commercial equivalent to Argos, though. I wonder what commercial equivalents there are... hmm, more research necessary.

There are some devices that are good for 10Km, but probably not much more... see

Ken

10 km would be quite optimistic for those devices.

The sensitivity is specified at -120 dBm, which is about the same as specified for NBFM radio telephones in the VHF range. These have typically 1-5 W of transmitter power and in portable operation with their own antenna, a few km of reliable coverage would be expected.

The original poster is apparently in Australia, so the 0,1 W output power for the Radiometrix module could be used, however, in Europe, only 0.01 W transmitter power could be used, thus reducing the range even further.

To realistically reach the 10 km distance, the other station would have to be high up in a cellular or water tower or alternatively, at both ends of the link, the antenna would have to be above the tree tops or on top of the buildings in urban areas.

If the system is intended for export, it should be noted that the regulations for various radio transmitting devices varies considerably, including allowed frequency bands, power levels, acceptance tests etc. for licensed and license exempt devices.

I would suggest using GPRS if it is available in the area.

Paul

Have a look at

- the modems will do 20-30 km depending on terrain and antennas, battery life would depend how much you want to transmit.

Tom

Yes, we make them. We put GPS engines on collars and transmit the data over RF. In order to get the kind of range you're looking for, you have to have special transmitters and receivers and nice conditions. For example, our Osprey model has 150dB gain. It's a small (one-handed), water-resistant, battery-powered receiver. We get 50 miles / 80km with ideal conditions with a good antenna.

If people, mountains, rain, animals, trees, rocks, buildings, cars, etc are in the LOS, you'll get reductions in range.

As for batteries, there are lead-acid batteries and there are Lithium cells. How much weight can you afford?

How much data do you want to send? Beyond certain thresholds - which are very small - the data can get corrupted very easily. Small amounts of data (10-50 bytes) work very well.

Someone else mentioned Argos - we have our own Argos PTT, and we do sell them seperately and/or to third parties. Trust me, you do not repeat NOT want to make one yourself.

--
Magnus McElroy
Electrical Engineer (EIT)
HABIT Research
http://www.habitresearch.com
(250) 381-9425

Thank you very much for the "Argos" link. I have found it very interesting. Following link from the Argos' web site provides a list of transmitter manufacturer for the Argos system

My intented implementation in the original posting/question is a semi-controlled baloon. Because of the very limited weight carrying capability of the baloon, we can not carry big, high power transceivers. Transmitters for the Argos' system could be very small (as light weight as

7gram t be carried on a bird . But because our implementation requires two way communication and we do not have the oportunity to wait the next pass of the Argos' satellites over Australia, unfortunatelly Argos system does not seems to be applicable in our case.

So I'm still looking for * Long range (10-100km) * Low bitrate (1200-19200 baud) * Small * Battery operated * radio transceiver units to send/receive digital data to be used between a semi-controlled baloon and a ground station for telemetry and control application.

Why didn't you say that in the first place ?

It makes *ALL* the difference if the stations are down in the ground clutter of if you have a free line-of-sight path.

So apparently you only have the weight restrictions on the balloon system, not on the ground system?

Do you have power restrictions on the ground system ?

Could you use directional tracking antennas on the ground ?

With such applications, I would suggest that you stay away from the license free bands and get a dedicated frequency (pair) with a sufficient power limit (say 1-100 W) for the ground transmitter from your telecom authorities.

For the control functions, you might even consider systems intended for model aircraft control and use a completely separate system for telemetry downlink on a different frequency band and thus be able to continuously communicate in both directions. You might even set up multiple telemetry receiving stations on the ground at different locations.

Paul

These people would seem to have trod the same path already

I suppose he could have his receiver up a tethered balloon too to increase line of sight.

A few suggestions:

- Contact your aviation authorities early in the project. You might get some useful hints.

- Contact your telecom authorities early in the project. You might get good suggestions of what kind of systems to use and what _not_ to use. If this is a one off launch, you might even get dedicated frequencies for the launch with generous power limits etc.

- I would suggest keeping the command and telemetry circuits separate, i.e. keeping both unidirectional at the protocol level, i.e. no ACKs transmitted back at the protocol level.

If the telemetry is constantly transmitted, try to grab as much as possible, but do not expect 100 % capture.

The telemetry could be sent on a license free band (check your local telecommunication authority if this is acceptable for airborne systems) and use a steerable high gain receiving antenna to recover the telemetry. There is no limitation on the receive only antenna gain that can be used and thus it is easy to attenuate any local noise source from similar equipment in the same band.

Use some telemetry inputs to monitor the command receiver outputs.

When you want to command the balloon, blindly and repeatedly send commands to the balloon and monitor the telemetry for the command receiver outputs. When the command receiver output has changed, you can stop sending that command.

If the balloon is going to ascend to say 10 km, the radio horizon will be about 400 km away and practically any station within that 500000 square kilometers (larger than most European countries) will be in LOS path. If you are using some shared frequency bands, be prepared to compete with all other transmitters within that frequency range. Thus, I would _strongly_ suggest that you get a dedicated command frequency for your balloon.

Regarding the problem of a hill 50 m high at 1 km distance as someone pointed out, I actually live 1 km from a sandy ridge created by the Ice Age, which is 50 m higher than my balcony and 70 m above a nearby lake. It is one of the steepest hills within a few hundred kilometers. While I agree that it is hard to get any signals from that direction, I am also very happy, since by climbing that hill, I can make VHF/UHF contacts from 100-300 km with 2-5 W transmitter power and a 10 dB yagi antenna.

If one would be fortunate enough to have such a hill close by, I would strongly suggest moving the balloon telemetry station on such hill.

Paul

Another low bitrate satellite service that is available worldwide is Inmarsat D+. This provides bi-directional communication to small mobile terminals most places more that 5 degrees away from the poles. The smallest terminal available is the SAT-201 which is around 4.5 inches in diameter and 2 inches tall. More info from

Ian

Thank you for the link and information. It is very intereting. On their brochures

they say data transmission rate from terminal to satellite is ~10bits per second and receive bitrate is 9 bits per second. They also say "By pressing a panic button, the message transmission frequency can be dramatically increased - for example, to every few minutes, to provide Search and Rescue authorities with rapidly updating position reports." which is very good for the applications given in their web site.

I'm afraid our applications requires almost continious communication between ground station and balloon at 1200-19200 baud and that's why Satamatics's terminals would not be appropriate for our application. But it is good for me to learn the existance of such an alternatives. Thank you.

How they charge their services? Does cost defined by the amount of data communicated ? Do you know how much it cost?

Thank you

Leo

Thanks - Magnus pointed me to Skywave's Inmarsat-D+ products, and that kind of opened the funnel for me, I've been looking at all sorts of options. They basically fall into three categories:

• Argos - restricted use (my application is probably eligible), 256 bits uplink only, low power requirements.

• Inmarsat D+ SMS - bidirectional telemetry and command information. It would also be possible to use a prepaid [voice] satphone's SMS capabilities to do the same thing, possibly cheaper (Skywave hasn't returned my emails asking for pricing info).

• Other satellite data services (R-BGAN, Inmarsat mini-C, etc etc). Would allow full uplink of image data as well as low-bandwidth telemetry. I would never need to recover the vehicle if it had this fat a satellite pipe.

The eye-opener for me is that all this stuff is really COTS and really cheap (compared to what I thought it would cost, anyway); it looks as if