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.