Aerospace and Electronic Systems - March 2019 - 33

controller, transmitter, transmitting antenna, and battery
[8]. All the electronic parts and battery are put in a thermal
protection box to maintain the inside temperature within
the allowed limits. Atmospheric pressure and relative
humidity are measured by the micro electro mechanical
systems based pressure sensor and the polymer-based
capacitive humidity sensor, respectively. The temperature
measurement is done with the help of a glass bead thermistor of small size. The outputs from the sensor circuits are
processed by the ADC. The GPS receiver module with integrated patch antenna gives altitude, time, location, and
velocity of the balloon/sonde by processing the received
signals from GPS satellites. The microcontroller reads the
ADC and GPS data and generates the telemetry data frames
for transmission. Reed Solomon forward error correction
coding is used to improve the data reliability [9] and cyclic
redundancy code is used for data integrity [10]. The specifications of Pisharoty sonde are given in Table 1 [8].
The digital telemetry data is modulated on a carrier
with frequency programmability in the range of 400-406
MHz which is the internationally allotted band for
Radiosonde operations [5]. The type of modulation used is
frequency shift keying (FSK) [11]. The radio frequency
signal is suitably amplified to the required power level

Figure 1.
Schematic of Pisharoty sonde system.

MARCH 2019

and is transmitted with the help of an omnidirectional
monopole antenna [12].
Two AA sized batteries are used to power the
Pisharoty sonde, with capacity for more than four hours
operation. At higher altitudes (upper troposphere) the
atmospheric temperature falls to around À85 C [13].
The temperature of the electronics parts should be kept
above À40 C as per specifications. For this purpose, all
the electronic parts and battery except sensors are kept
inside a thermal insulation package. The block schematic
and photograph of Pisharoty sonde are shown in Figures 2
and 3, respectively.
Ground station consists of receiving antenna assembly
with low noise block (LNB), Pisharoty sonde receiver and
data processing and display software installed in PC. On
establishing the connection with the receiver via Ethernet
interface, the processing and display software acquires,
processes, stores, and displays the data. The data can be
displayed in numerical or tabular form.
Two independent antennas, one monopole and one
quadrifilar helix [14], mounted on an elevated platform,
are used to receive signals from the balloon-borne sonde.
The dual antenna system ensures uninterrupted signal
reception throughout the sonde ascent, without any
mechanical movement, as the radiation patterns of the
two antennas are complementary and cover the entire
hemisphere as shown in Figure 4. The output of each
antenna is fed to LNB, which is installed near to the
antenna, for sufficient amplification of the received signal
to cater to the signal attenuation caused by long interconnecting cables to the Pisharoty Sonde Receiver.
Pisharoty sonde receiver is a low-cost dual-channel
receiver for simultaneous reception and demodulation of
signals from both antennas. The data from both channels
are processed by the front end software in PC/Laptop and
displayed in real time as physical parameters. The block
schematic and photograph of Pisharoty sonde receiver is
shown in Figures 5 and 6, respectively.
The Pisharoty sonde system has features like frequency programmability, balloon burst indication through
ascent/descent rate variation analysis, sonde switch off
based on prefixed time/altitude for frequency reuse, etc.,

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Aerospace and Electronic Systems - March 2019

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