DISCUSSION AND CONCLUSION

We have shown how a software defined receiver for radiosonde application can be built with the help of commercially available RTL-SDR and LabVIEW. The advantages of the developed receiver are quick development time, modularity and mobility. Design of Quarter-wave monopole and QHA antennas to be used in receiver system is also discussed to help the researchers and hobbyist to establish their own receiver for radiosonde application. The sensitivity of the RTL-SDR based receiver is evaluated for different data rate and frequency deviation values. Further to establish the maximum distance for which receiver can receive the data, real time radiosonde flights are used.
Results showed that minimum SNR value of 20dB is required to achieve BER of 10-4. SNR measurements with respect to radial distance of transmitter shows that when RTL-SDR receiver is coupled with monopole antenna it can receive the data up to about 65-70 Km. and when coupled to QHA data could receive up to the range of 75-80 Km. Further from the analysis of one year of radiosonde flights at NARL it can be confirmed that RTL-SDR based receiver is a good contender to implement a low cost receiver for meteorological balloon telemetry system. However few improvisations such as inclusion of Reed-Solomon decoder, metallic enclosure for RTL-SDR, a band pass filter at front end and use of low loss RF cable etc. can be used to make the receiver system further robust and reliable. Further it is possible to implement that two channel receiver using two RTL-SDR devices fed with monopole and QHA for hemispheric coverage with little modifications in software.