From Atmosphere Research
Transmitter are one of two main components of our telemetry system. At the operation of free flying measuring probes, the scientist always faces the same question: How do I get the measured data of my system? Our transmitter, together with our ground stations, form a closed data transmission system. The communication is done over a coded radio network, so only our ground stations are able to work with our transmitters and vice versa. To reduce the technical effort for the user these two main components are available as complete packages, which contain all necessary parts and functions to operate a probe with this telemetry.
The transmitter are specially designed to be used on small research balloons, where the available space and payload weight is very limited.
With data transmission rates of 160 kBaud, they are nearly 10 times faster than other systems. That's why our telemetry, for the first time, allows to fly measurement systems even with high sample rates respectively high measure resolutions and nevertheless transmit the data live and entirely to the ground station!
The capacity of this transmission is still not fully exploited, but for higher data rates we always have to go into a compromise with a lower range.
At the same time the transmitter do also form a complete operational support platform for a connected measurement system.
The aim here is to provide all functions normally needed by any slave system, which can be used nearly 'plug & play'. This way the user (scientist) does not has to think about the development of these support systems and is able to focus on his actual area of expertise, the measurement system.
- very small, very light
- with or without case
- support of multiple ground stations, this way any range can be reached
- downlink for user data and status information
- uplink for control commands, direct control of the transmitter and the connected devices
- 16 MByte internal memory (buffer during connection losses)
- high transmission reliability (packet loss rate < 1%, despite of frequently connection losses of several minutes)
- live data transmission
- integrated GPS without COCOM limits
- 2 programmable voltage sources
- 2 digital interfaces
- power supply over internal battery pack (charger integrated) or an external power source
- 7 free programmable digital/analog input/output - pins for control and measurement tasks (planned)
- second radio channel for higher transmission capacity (planned)
The system has additional unused resources, like internal hardware interfaces, which are reserved for future expansions.
- input voltage range 7 - 22 V DC
- max. power consumption 5.5 W (without load on the voltage sources)
- temperature range -40 - +85 °C
- GPS limits < 50 km altitude
- voltage source 1 1.2 - 5 V, 500 mA
- voltage source 2 1.2 - 12 V, 500 mA
- weight (without case and cables) ca. 90 g
- type 2x 2-cell LiPo (7.4 V, vacuum suitable)
- capacity 4000 mAh, 30 Wh
- min. charge input voltage 12 V
- charge current intern 1 A
- charge power 9 W
- weight ca. 170 g
- Digital interfaces 2 (1x system control, 1x user data stream)
- interface types optional currently: USB, RS232, RS422, RS485 (planned: CAN, LAN)
- baud rates up to 256 kBaud
- radio - frequency band standard: 869 MHz (optional: 920 MHz, 2.4 GHz, 3.4 GHz)
- radio - output power up to 1 W
- radio - data rate 160 kBaud
- radio - range over 100 km (at 869 - 920 MHz), over 50 km (at 2.4 - 3.4 GHz)
- antenna type stab antenna
Our transmitters, or the entire telemetry system, was designed to operate where large among of data have to be transferred between two places over a long distance, but no local infrastructure is available or not intended to be used. A concrete example are measurement systems on board of free flying research balloons, which measured data have to be transferred to the user on the ground directly.
The transmitter's characteristic to provide not only a fast telemetry, but also to function as a complete operative platform for the connected measurement system, makes them particularly versatile.
The following describes some typical operation scenarios (see also the application part of our ground stations):
- Thanks to the 2 programmable voltage sources, the instrument can be supplied directly from the battery pack of the transmitter. This safes space and weight, because there is no need for additional batteries and supply electronics.
- These sources can also be configured during the flight, so it's even possible to switch on or off parts of the measurement system (for example to safe energy).
2. Extensive control of a complex measurement systemSituation: A complex measurement system with it's own data processing and control unit has to be operated with the transmitter. The measurement system has several different sensor units.
- Over the uplink of our telemetry, the user is able to transmit any desired message. Correct coded system commands are executed by the transmitter itself, all others will be forwarded over the two digital interfaces to the connected devices. Responses of these device also will be registered and then, independent from the user data stream, forwarded through the radio connection to the ground station and the connected PC.
- So the user is able to communicate with his measurement system completely transparent, like over a serial connection and can influence its behaviour instantly.
- For example, the user could take spontaneous decisions about the sensor operation based on the received live data, like switch sensors on or off, trigger one-shot measurements, change sample rates or measuring ranges, run fine tuning or calibration procedures, request status information, all independent from the user data stream
- A disrupted frequency band is an essential problem for each telemetry. The information of the transferred data could get modified, transmission packages could get corrupted and lost or the connection between ground station and measurement system breaks down completely.
- Our telemetry - system uses several processes to compensate such noise (like frequency hopping). Additionally, failed package transmission are repeated. For this purpose the transmitter provide a large internal memory of 16 MByte, which buffers the incoming user data stream, until it is able to be transmitted successfully.
- That means a very noisy environment of course has a negative influence on the effective transmission rate of the system, but it can be ensured, that only very few data are actually lost.
- The behaviour of this buffer and the transmission are able to be modified by the user to adapt them to the environment conditions and the requirements of his experiment.
- Even this is possible, under some limitations
- The max. transmission rate is 160 kBaud, wherein the effective rate can be less, depending on disturbances. Is the input data rate at the transmitter's interfaces greater than the current transmission rate, then the user data are buffered in the internal memory.
- Thanks to the command uplink of our telemetry, this behaviour can be used to deal with even higher data rates for a limited period of time. During the launch and climb phase the measurement system operates with less data rate, so that the buffer keeps empty. With the live data and the GPS position and altitude the user is able to decide, when the balloon enters the especially interesting area or flight phase for his experiment. At this point he can send the remote command to set the sample rate to its maximum. Now the recorded data are still transmitted with the maximum available transmission rate, while in the background the buffer stores the supernumerary incoming data. Of course, as soon as the buffer is full, data will be lost. At this point the measurement system should be switched back to the low sample rate to give the telemetry a chance to empty the buffer again.
- Equip the measurement system with a cutter, which can be remote controlled and separates the instrument from the balloon, so that the flight can be interrupted any time.
- Over the uplink and the controllable outputs of the transmitter this cutter can be triggered selectively.
- The telemetry provides the live monitoring of the current flight data, therefor also the transmitters integrated GPS can be used.
- The measurement instrument is connected to the user data interface of the transmitter.
- The control system of the glider is independent from the measurement and connected to the command interface.
- Parallel to the user data stream and the flight data updates over the downlink the uplink can now be used to send control commands to the gilder control system. This way one could set a new target for an auto pilot system or even a direct remote control of the gliders flight behaviour is imaginable.