Beacon transmitter

It´s now time for me to give you a short summary of the work that has been done concerning the Radio beacon. But I’d first like to give you a motivation of why the beacon is so important for those of you who need a short reminder off the construction of our experiment please take a short look at Så vad är det vi ska göra egentligen? / So what’s all this about then? (please note though that we’ve changed from airbags to parachute for the landing system).

Since all the data that will be recorded after the FFU has separated from the RMU will be stored onboard of the FFU it’s a primary objective to be able to find the FFU after it has landed. To track the FFU two different systems has been integrated into the FFU. The first system is a GPS which receives the current coordinates of the FFU while in flight. The coordinates are then transmitted through a satellite modem and are then received through a web interface. The second system is the beacon transmitter. A beacon transmitter is a consists of a simple radio transmitter who transmits a signal in an devoted frequency. This signal can then be tracked by a simple receiver. The tracker/receiver consists of a simple radio receiver working at the same frequency as the transmitter  and a simple analog meter displaying the strength of the received signal. By pointing the receiver antenna at different directions is simply its possible to track in what direction the transmitter is located.

In practice the system used by SQUID consists of the TX1 transmitter from Radiometrix. The transmitter makes use of a simple quarter wave whip antenna (which in reality consists of a stripped coaxial cable). For the experiment the beacon will be sitting within the eBox while the antenna is attached to one of the parachute ropes. The transmission is done over 169.4125 MHz and is then received by the receiver.

TX1 transmitter

To test the transmitter function a NRX1 receiver, from the same company making the transmitter, has been bought. This transmitter will be integrated into a simple circuit. The idea is to make use of the Received Signal Strength Indicator (RSSI) which is provided by the receiver. The RSSI works by providing a voltage on one of the legs of the receiver which varies depending on the strength of the received signal.  The circuit will consist of battery holder, power switch, the receiver, analogue current meter and a receiver antenna. The analogue current meter will be connected to the RSSI pin and will vary by the signal strength of the voltage provided by this pin.

NRX1 receiver

The testing will start during next week and will be rounded of by the drop test. During next week a simple transmitter circuit will be built including the transmitter, a power switch, antenna and battery. The testing will start of by placing the transmitter in the Lilian wood nearby KTH, the receiver will then be used to try to find the transmitter. I hope to have some more info about the progress of these tests shared to you all during next week.


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