This is a most interesting project you would like do. its just hunting down the fox the over here is a transmitter this project includes both transmitter as well as receiver , and the main goal of the project is to keep track of some moving objects or animals . This sought of arrangement is generally seen in wild animal tracking systems where the rangers keep track of the animals to take care of there number and to protect them from poachers.
Receiver :
Antenna Design
The antenna used in the receiver is a YAGI antenna. A YAGI antenna is a
Directional antenna which consists of three main elements reflector, dipole and directors.
In our antenna we have four directors with specifications as in fig-1.The reflector and the
directors’ drive the signal (E M waves) coming in direction of director towards the dipole
and so the signal in one direction (from director to reflector) is picked up maximum which
makes the antenna behave as a directional antenna. The more the number of directors the
more is the gain.
Specifications
Operating frequency……………………………... (MHz) =145
Reflector length…………………………………….... (m) =1.06
Fed element length…………………………………... (m) =1
Reflector Spacing……………………………………. (m) =0.36
Number of Directors……………………………….......... =4
Element Diameter………………………………….... (m) =0.01
Director Spacing (m) Length (m)
D1 .25 .97
D2 .43 .94
D3 .33 .93
D4 .43 .89
Forward Gain……………………………………….. (dB) = 11
Forward to backward ratio…………………….. (Const) = 29.45
Input impedence………………………………...... (Ohm) = 32.4 + j 0.4
Array length…………………………………………. (m) = 1.80
Circuit Description:
The FM receiver is designed using the popular Sony chip CXA1619BS used for
AM/FM receiver circuits. The chip is a 30 pin dual-in–line package with the following
functional blocks :
· Front-end block (RF amplifier, mixer , oscillator)
· IF stage
· FM discriminator
· AF Power amplifier
The transmitted signal is picked up by a high gain and high directivity Yagi –Uda antenna
(described in page 1) designed to pick signals around 145 MHz frequency.
The signal from the antenna is fed first to a Band Pass Filter which suppresses adjacent
channels and allows only the selected high frequency signal. The Band pass filter used here
is a LC circuit designed as below.
Band Pass Filter:
C1 = C2 = 7 9.6 pF Resistor load = 1K
L1 = L3 = 0.015 μH Frequency = 145MHz
L2 = 159.15 μH Loaded Quality factor=72.5
The signal at the output of the Band pass filter is fed to the circuit shown in fig -5 which
consist of chip CXA1619BS.
Chip Structure:
The internal building blocks of the IC can be observed below in fig (4)
Circuit operation:
The signal from band pass filter is fed to FM RF IN pin 13 of the IC. The tuning of
the signal is done by selecting the RF frequency and the local oscillator frequency with the
help of L2-C2 and L3-C3 tank circuit respectively. Fine tuning is done through ganged
capacitors. The heterodyning is done in the FM FE block which generates the IF signal of
10.7 MHz. The signal through FM IF (pin 18) is now sent to the FM IF block inside the
chip .This is done only after it is passed through a 10.7 MHz Ceramic filter (CF2).
The FM IF selects and amplifies the IF signal and generates the AF signal using the
FM discriminator block .The output of the IF block is the audio signal that is delivered to
pin 22 and then to pin 25 (AF IN) through a coupling capacitor. The FM discriminator is
tuned to 10.7 MHz using the ceramic/crystal resonator (CF3). The AF signal (demodulated
output from IF block using the FM discriminator) is further amplified (to drive the ear
phones) by the AF power amplifier. The volume at the output (ear phone) is controlled by
using a variable resistor (potentiometer) of maximum 50kOhm resistor RV1.The audio
signal is then fed to earphone through pin 28 and capacitor C21.
This was built for a competition at iit bombay.
