1. Radio Receiver Design for Unmanned Aerial Wildlife Tracking
Daniel Webber*
, Nathan Hui†, Ryan Kastner†, Curt Schurgers†
*Santa Clara University, † University of California San Diego
Abstract
The use of radio collars is a common method wildlife
biologists use to study behavior patterns in animals.
Tracking a radio collar from the ground is time con-
suming and arduous. This task becomes more dif-
ficult as the size and output power goes down to
accommodate animals as small as an iguana. Our
solution is to fly a low cost Unmanned Aerial Sys-
tem equipped with a sensitive receiver chain to lo-
cate several transponders at once. The challenge is
that the system needs to be low cost and be able
to detect the transponder within a range of tens of
feet. Initial ground tests indicate that the system
was able to detect a collar 70 feet away for under
$100.
Background
Currently we have partnered with the San Diego Zoo
to build a proof- of-concept and deploy it in the field
to learn if this is a viable solution [1]. Compared to
current methods of tracking a single radio collar at a
time, this we envision a system able to track multi-
ple collars simultaneously with the help of Software
Defined Radio (SDR). To accomplish this we need
to not only reevaluate the way the receiver is built
to track multiple collars, but also develop a system
to detect such collars from an effective range.
Figure: A prototype version of the UAS equipped with the
receiver.
Receiver Overview
For the system, several different components inves-
tigated to test whether they are sensitive enough
to detect the radio collars at an adequate range
while staying within a reasonable budget and physi-
cal footprint. The components that were considered
and investigated were:
• Antennas
• Low Noise Amplifiers
• Software Defined Radios
Software Defined Radios
The Software defined radio was chosen for its’ versa-
tility, large instantaneous bandwidth and form fac-
tor. While industry standard SDRs are available,
they were too heavy for the UAS or cost prohibitive.
More recently lower end SDRs have been created
from a popular chip set found in digital TV dongles.
Many versions of those SDRs were evaluated for
sensitivity, accuracy and their response to external
noise. The NOOELEC SDR, Airspy and RTLSDR
are the ones we evaluated.
Figure: The Airspy SDR along side with the NOOELEC SDR.
Antenna Design
To implement the system, an Omni-directional an-
tenna was needed. A dipole antenna was chosen
for its’ good omni directional pattern. Our primary
method was to derive a design from simulation soft-
ware. ANSYS Electronics Desktop was chosen to
achieve this.
(a) S11 Parameters Simulated from ANSYS
(b) S11 Parameters Results from Vector Network Analyzer
Figure: S11 Parameters Simulated Versus Measured
LNA Testing
Radio Noise Floor (dbm) SNR
Airspy -74.1 14.1
Airspy LNA -36.9 37.2
RTLSDR -59.6 5.4
RTLSDR LNA -36.0. 29.0
Table: LNA SNR Measurements on a Mini-Circuits,
PSA4-5043+ LNA.
Range Testing
Figure: SNR to Distance of each Configuration. Note ARRL
dipole is a non-simulation based design method created by the
American Radio Relay League
Range Testing
While each of these systems have been tested indi-
vidually, a field test was put together to look at all of
the systems together to better determine if these im-
provements found in the lab translate into the field
with actual radio collars. Due to recent government
regulations and logistics, flying a UAS for research
purposes have become difficult, so all of these tests
were not carried out on a UAS. Instead, a range test
for each system was designed to indicate the maxi-
mum distance possible where one could still detect
the collar. We developed a method to investigate all
iterations of the system and compare each in a rela-
tive manner. From our initial results it was obvious
that some systems outperformed others.
Conclusion
From simulation and physical testing, we demon-
strated that building a low cost and sensitive receiver
chain is attainable. The field tests demonstrate the
potential of the system.In order to determine if this
is a competitive alternative to aerial tracking, addi-
tional field tests will need to be conducted.
References
[1] G. A. M. d. Santos, Z. Barnes, E. Lo, B. Ritoper,
L. Nishizaki, X. Tejeda, A. Ke, H. Lin, C. Schurgers,
A. Lin, and R. Kastner.
Small unmanned aerial vehicle system for wildlife radio
collar tracking.
In 2014 IEEE 11th International Conference on Mobile
Ad Hoc and Sensor Systems, pages 761–766, Oct 2014.
Acknowledgements
The authors would like to thank the San Diego Zoo for provid-
ing valuable support, insight and the specific hardware that
is currently used for VHF tracking. This work was funded
in part by NSF REU Site: Engineers for Exploration, Grant
#1560162 and Grant #1544757.