Current Journal of Applied Science and Technology

Volume XXX, Issue XX, Page XX-XX, 2022; Article no.CJAST.97073

ISSN: 2457-1024
(Past name: British Journal of Applied Science & Technology, Past ISSN: 2231-0843,
NLM ID: 101664541)

Design and Implementation of FM

Transmitter for Security and
Communication Purpose at the Coast
General Hospital Wards
Nyamieri, Dominic Ondieki a and Mosiori, Cliff Orori a*
a
Department of Mathematics and Physics, Technical University of Mombasa, P.O. Box 90420 –
80100, Mombasa, Kenya.

Authors’ contributions

This work was carried out in collaboration between both authors. Both authors read and approved the
final manuscript.

Article Information
DOI: 10.9734/CJAST/2022/XXXXX

Open Peer Review History:

This journal follows the Advanced Open Peer Review policy. Identity of the Reviewers, Editor(s) and additional Reviewers,
peer review comments, different versions of the manuscript, comments of the editors, etc are available here:

Received: DD/MM/20YY
Original Research Article Accepted: DD/MM/20YY
Published: DD/MM/20YY

ABSTRACT

An FM transmitter is a small electronic gadget that has a wire (aerial) that produces electromagnetic
radio waves capable of transmitting energy through at space. It creates recurring radio waves that
exchange in form of current which is then applied to receiving wire (aerial). At a point where signal
reception occurs, the radio waves get energized by a rotating current in the receiving wire. It is
therefore, a complex gadget considered to be a high voltage energy system. It design is complex
and thus demands critical maintenance procedures which are costly. In Kenya, there is rapidly
growing demand for the use of FM transmitters both among individuals and institutions alike. This
project was carried to design, construct and implement an FM transmitter that is cheaper to buy,
easy to maintain and expected to be equally efficient when in operation. An FM transmitter was
designed and constructed using the transistors, resistors, coils, capacitors and microphone. It was

_____________________________________________________________________________________________________

*Corresponding author: E-mail: cliffmosiori@gmail.com;

Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

mounted on testing symbolic bed assumed to that of the patient (at Coast Level Five Hospital) who
figuratively required the attention of medical personnel (doctor/nurse/caretaker). It was connected to
12V DC power source and tested. In this paper, we report the successful completion of the project.
Its findings are outlined and discussed. The results revealed that a locally designed FM transmitter
that operates on low power can be designed that has an appreciable range of signal transmission. It
was recommended that further investigations be carried out on the signal coupling circuit so as to
improve range of transmission further.

Keywords: Coast General Hospital; LC Tank circuit; BJT; Oscillator circuit; stable frequency; power
transistors; amplifiers; coupling capacitor; emitter resistor.

1. INTRODUCTION if a FM transmitter is designed and implemented

that performs at low voltages. If efforts are not
In the recent times, the world has entered an era made to produce an FM transmitter that is
referred at as “information age” [1] when uniquely affordable easy to maintain and efficient enough
modified electronic communication systems are and yet operates on low power, the desire to
influencing on how we live and operate. achieve simple and affordable radio broadcasting
Frequency modulation (FM) transmitter provides remains a mirage. A transmitter in the world
greater signal to noise ratio than amplitude today [6] is composed of a power supply, an
modulated (FM) transmitter for the same antenna oscillator [7], a modulator, amplifiers for audio
input. FM transmitter has been adopted by frequency (AF), intermediate frequency (IF) and
governments and state parastatals as a means radio frequency (RF). They consists of three
of radio broadcast for public enlightenment major aspects; the receiver, the channel and the
campaigns, news and educational programmes. source which is the transmitter [8]. According to
As a follow up, a number of tertiary institutions Uchiyama et al. [1], with the aid of an antenna, it
and private companies that are attempting to propagates RF signals such as radio, television
engage in electronic media [2]. The demand for or other telecommunications [9] from one
the use of FM transmitter is constantly growing position to another for purposes of
among private individuals and institutions or communication. Against this background, the
cooperate societies. Locals and communities TUM research team took up the challenge and
wish to share news independent of government designed, constructed and implemented an FM
control but under regulatory bodies [3]. However, transmitter gadget that incorporated a very high
this normally requires complex equipments [4] frequency (VHF) power transistor No. 2C1971
that are also high power consumers or require (NTE343) at the output stage. In this paper, we
high voltage design systems whose maintenance report on a project prototype design of a FM
costs are exorbitantly high. According to Fathy et transmitter that make use of 12V DC power
al. [5] an FM transmitter requires large currents supply but able to generate RF signals for local
at high voltages of up to 20kV. Such transmitting broadcast with enough power to propagate a
stations experience higher over-voltage risks in distance of over 70 meters.
their towers. However, Basu, & Bhowmik, [2]
noted that high voltage power supply system 2. THEORY
designs are probably the major challenge for
players in FM signal transmission. A number of Transmitters are classified according to how they
challenges experienced by FM transmitter have process and radiate signal information [5]. A TV
become an impediment to individual payers and transmitter processes and radiate sound and
institution that wish to adopt FM radio broadcast picture signal [10]. Radio transmitter processes
as an electronic media of communication tool. and radiate sound signals only [1]. An FM
These individuals, institutions and organizations transmitter is a low power type of transmitter.
lack enough allocated funds to develop .or According to Uchiyama et al. 2020, it requires an
purchase and maintain complex transmitting oscillator tank circuit to generate the radio
stations. One of such an institution is the Level frequency carrier waves. It uses VHF radio
6 8
five, Coast General Hospital, in Mombasa frequencies of from 8.8 ×10 Hz to 1.08×10 Hz
County. to transmit and receive FM signals [5]. Modern
Frequency Modulated signal transmission
At the Coast General Hospital, in Mombasa requires the action of an audio pre-amplifier [11],
County, Kenya, this dilemma could be sorted out a unique signal modulation process and then

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

transmission ability. Its wireless performance and where, f is the modulated frequency output.
working mechanism depend on the inductor coil
& the variation of its capacitance [12]. It transmits
d c (t ) (6)
the audio signals through the carrier wave by the
difference of frequency. At the microphone edge
W1   2f1
dt
[13], a very low audio signal is first generated. It
is then amplified to produce an inverted amplified
When equation (6) is differentiated w.r.t velocity
signal by a bipolar transistor whose common-
of output we obtain equation (7) as [3];
emitter configuration is biased to operate in the
class A region [6]. The audio input signal from
d c (7)
 2f c  2f
the microphone enters the base of the transistor
resulting into a modulated FM carrier signal. The
audio input signal from the microphone enters dt
the base of the transistor resulting into a
modulated LC tank circuit carrier signal [14] of a reducing to Eq. (8) as;
FM in nature. In general, the audio signal is first
amplified by an oscillating circuit, amplified by an
amplifier and processed by a variable frequency d c (t )  2f c dt  2fdt (8)

oscillator circuit within the frequency range.

When the Colpitt LC oscillator circuit [13] is given and integrating Eq. (8) gives Eq. (9) which can
a voltage input, it generates RF signals that further be reduced to Eq. (10),
oscillate between an inductor and a capacitor. It
then mixes with a small input signal producing an
 c (t )  2f c  dt  2ka Vm (t ) dt
(9)
overall modulated output signal which is
proportional to the real baseband signal
expressed as [8];
 ( c ) (t )  2f c  dt  2kaf  Vm (t ) dt
(10)

C ( t )  Ac cos  c ( t ) (1)

The instantaneous voltage varies as in Eq. (11)

as
 c ( t )  2f c t   (2)

V(t )  Vpeak cos(2f mt (11)

where A is the amplitude of carrier, Өc(t) is the
angle of the carrier while  is the phase of
carrier signal. This signal power is further Hence resulting into Eq. (12) as;
amplified by a power amplifier and the output
signal is then matched with an antenna set at low 2f c t  2ka (12)
d c ( t ) 
2f m sin2f m t 
impedance output [6]. When the Voltage Control
Oscillator frequency fc, and the input voltage is
Vm(t) are regulated, they can be expressed as Eq.
(3) and Eq. (4) respectively as [13]; Reducing to Eq. (13);

V  Ac cos (t ) 2f c t  ka
(3) (13)
d c (t ) 
f mV peak sin2f m t 
And
Such that amplification and voltage can be
f1  f c  f
(4) expressed by Eq. (14) and Eq. (15) respectively
as;

(14)
Resulting into a shift in frequency in Eq. (5) as; V peak
m f  2 
f  k a  Vm (t ) fm
(5)

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

V  Ac cos c(t ) (15) components and devices that included resistor,

capacitor, trimmer capacitor, inductor,
microphone, diodes, transmitter, and antenna in
Thus, forming Eq. (16) which is commonly which its output stage operated using the VHF
referred to as the voltage of FM transmission NTR 342 transistor circuit.
expressed as;
These components were inserted after correctly
Ac cos(2f c t  ka (16) identifying their designation terminal and polarity
V identification joints. The FM transmitter employed
f mV peak sin(2f m t ) the transistor 2N2369 which is a 250 mW power
output stage as shown in Fig. 3.
Using this voltage in Eq. (16), the variable Its oscillating tank circuit employed the NPN
capacitor changes the resonant frequency to an transistor of 2N3904 amplify that was coupled
FM frequency band. The final modulated signal with an inductor and a variable capacitor. The
from the antenna is radiated outwards in the form design was to ensure that when a current is
of FM radio waves of a specific frequency band. passed through at the variable capacitor and
inductor, L1, the oscillating tank circuit oscillates
3. METHODOLOGY at resonant carrier frequency (FM) such that its
negative feedback exits through capacitor C2 to
3.1 Components the oscillating tank circuit. The microphone was
connected to a coupling compactor C1 so as to
Some of the electronic components used in this feed a signal to the base of the transistor Q1. All
study included the Omni-directional microphone, the other components were mounted 5mm above
transistors, various capacitors, various resistors, the panel board and trimming of the excess leads
100 m copper wire, an IC Omni antenna, battery was well done immediately after soldering.
as a power source, PC board, and FM receiver.
The power source in this study was from a 12 V 3.3 FM Amplification Circuit
DC source.
Fig. 3 shows the amplification circuit. The design
3.2 FM transmitter Component Layout used resistors, capacitors, a trimmer capacitor,
audio signal output, and audio-antenna to form
Fig. 1 shows the block design diagram for the FM the amplification stages [15].
transmitter circuit assembled from the electronic

Fig. 1. Block diagram for the transmitter layout

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

Fig. 2. FM Transmitter Circuit

Fig. 3. Circuit of amplification/Receiver/alert/doctors desk (Basu, & Bhowmik, (2020))

A NPN Bipolar Junction Transistor, BC109 that circuit that undermines performance. A 30 x 30 x
operates at about 9V was selected to assemble a 15 cm plastic casing was adopted as a cabinet
pre-amplifier circuit. The quiescent collector casing to accommodate all the primary inputs.
current was determined and adopted. The Load
Resistor, R4 was determined. The bias current 3.4 Testing of the Design
and voltage across the load resistors was
determined as being about 10 times the base The following tests were performed according to
current to form the Voltage Divider Resistors R2 IEE Regulation, 1988 and the findings were as
and R3. Every component was carefully and follows: the continuity test which was to detect
neatly soldered using 40 watt soldering iron to any open circuits in the FM transmitter; static test
avoid being pulled out using a clean 60 watt to confirm transistor terminal voltages before
soldering iron to provide safety. Soft soldering completing the circuit to AC power source; the
since it is suitable for light points in copper and polarity test that was mean to confirm correct
electronics joint to avoid open circuit or short terminal connections and the transmitter range

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

test that was meant to determine how far the FM the collector current divided by the current gain,
signal was to be sent and be received. After hfe. This resulted into a base current (Ib) of 0.08
carrying out all other tests, the last test before mA as regulated by the voltage divider resistors
the connecting the designed FM transmitter to an R2 and R3. This gave a voltage of 0.7V across
AC power source, a continuity test was carried the base, Vb which was also more than the
out. A world FM radio receiver turned to the FM emitter voltage (Ve). Hence resistor Vb/Ibias = R2
meter-band was tuned gradually to detect and resulting into 22.25KΩ. Here we select a 22K
capture an FM frequency from the prototype resistor so that (Vcc-Vb/Ibias = R3 giving 90.1KΩ as
design. Once it was detected, the receiver was a result, the emitter voltage 1.08V which was
slowly moved away from the FM transmitter till about 12% of the Vcc voltage. Hence, Vb voltage
the signal was just lost. The distance was was about 1.78V. The value of Emitter Resistor,
measured to the farthest point signal at which the R5, was determined from the relation Ve/Ie, by
signal was just lost. Power consumption was also taking the emitter current Ie as approximately
tested. equal to the collector current, Ic and it was
obtained to be 540 Ohms which served the
4. RESULTS AND DISCUSSIONS purpose of bypassing the emitter current, Ie. The
coupling capacitor, C1 served the purpose of
4.1 Transistor Tests modulating current going through the transistor.
Its value was obtained as 5 uF. Resistor R1
Testing of the transistor showed that when Served as a microphone resistor to limit the
junction is in forward biased (base/emitter), the current passing through the microphone, to a
ohmmeter recorded very low reading in level the microphone can handle.
millimeters but on reverse biasing the two
junction and both junctions read high. Using specifications of the microphone, the
Connecting in reverse between the collector and current average current allowed through
emitter, the ohmmeter recorded reading high. microphone was to be 0.4mA. Using the relation,
When the NPN transistor diode junctions used in (Vcc-Vb)/0.4 the microphone resistor Rm was
the design circuit, it was tested using a digital obtained as 18.05K. Capacitor C4 served as a
multimeter. It was revealed that the correct DC signal bypass capacitor and its value was
terminals were connected to an ohmmeter with obtained to be 15 uF. Inductor L1 and capacitor
the base connected to the positive terminal while C6 formed the tank circuit components. Its
the negative common terminal was connected to operating frequency oscillations was determined
the emitter. The static test revealed a number of form f = 1/(2π√LC). Since this was an FM
faults such as open circuit and short circuits in transmitter to operate at a frequency between 88
transistors and other sections which were MHz to 100 MHz, the inductance of L1 was
corrected. It further revealed that the transistor obtained as 0.2uH while capacitance C6 was
had the following parameters: the VC Collector determined as 12pF and varied between 5 pF to
voltage was 8 V with reference to the base; the 20pF actively during transmission. Capacitor C9
VB base voltage was 1.7V while the VE emitter formed the Tank Capacitor that served the
voltage wasc1.0 V with reference to the ground. purpose of keeping the tank circuit in vibration
during transmission. Since this project used the
4.2 Implementation BJT 2N222, it was obtained that during testing, it
varied 4 pF to 10 pF. After transistor polarity test,
R6 and R7 were found to bias resistor and
In this project, the NPN Bipolar Junction
through calculation, they were determined to
Transistor, BC109 was selected and used. In the
have a value of 9.1 KΩ and 40.03 KΩ
single stage common-emitter amplifier, the Vcc,
respectively. Capacitor C3 served the purposes
voltage was 9V. This was an appropriate voltage
of coupling and after determination; it was
since the VCEO for this transistor is around 40V.
obtained to have a value of 0.01 uF and this
The quiescent collector current was assumed to
resulted in the emitter resistor, R8 for the
be about 1mA and was used taking the collector
amplifier circuit to have a value of 1.04 KΩ. After
voltage of about half of Vcc based on Vc/Iq
a number of tests, the results showed that the
relationship. The value of the load resistor, (R4)
FM transmitter performed well on a DC power
was found to be 4.5KΩ and approximated to 5KΩ
supply of about 12 volts and in this case there
to protect the circuit. The bias current was
was neither any frequency drifts nor any
approximated to be 10 times more than the base
detectable electrical noises.
current so that the base current, Ib was equal to

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

5. CONCLUSION 65-nm CMOS. In 2020 27th IEEE

International Conference on Electronics
An FM transmitter was designed and Circuits and Systems (ICECS). IEEE.
implemented a low power output class A power 2020;1-2.
amplifier with an LC tank circuit at the output. 2. Basu D, Bhowmik A. Design and
The tank circuit components were of the same implementation of a smart & portable
magnitude as those in oscillator circuit. The wireless fm transmitter for wide range
biasing resistor was of about 20 KΩ while the communication. Journal of Engineering
coupling capacitor of about 10 pF. Using this Research and Reports. 2020;28-42.
design, the FM transmitter was able to send FM 3. Fathy AA, Said MH, Mohamed HA, Rasmy
signal to a distance of about 30 meters in radius. SS, Ellaithy DM. Low-power low-
It was concluded that a practical FM transmitter complexity FM-UWB transmitter in 130nm
that requires a low power input operating on 12 V CMOS for WBAN applications. In 2020
DC power supply can be designed and 15th International Conference on
constructed easily as an undergraduate project Computer Engineering and Systems
for local markets, hospital and even for use some (ICCES). IEEE. 2020 December;1-5.
learning institutions in Kenya. Following the 4. Benali S, Trabelsi H. Analysis of 25% duty-
successful outcome of this project, it was cycle up-conversion passive mixer for
recommended that Bachelors of Technology in UWB transmitter. AEU-International
Applied Physics (Electronics and Instrumentation Journal of Electronics and
- BTAP) students of in TUM should be Communications. 2020;123:153295.
encouraged to undertake the design and 5. Artem V, Volodymyr S, Ivan V, Vladyslav
construction electronic projects to enhance V. Research and development of a stereo
Kenya’s technological development in encoder of a FM-transmitter based on
technology. FPGA. In International Conference on
Computer Science Engineering and
SOURCE OF FUNDING Education Applications. Springer Cham.
2018;92-101.
The project was funded by the University Council 6. Lewis MS, Crandell CC, Kreisman NV.
and Management of the Technical University of Effects of frequency modulation (FM)
Mombasa through the Partnerships, Research transmitter microphone directivity on
and Innovation office. speech perception in noise; 2004.
7. Ando N, Shimoyama I, Kanzaki R. A dual-
ACKNOWLEDGEMENT channel FM transmitter for acquisition of
flight muscle activities from the freely flying
The authors wish to acknowledge the University hawkmoth Agrius convolvuli. Journal of
Council and Management of the Technical Neuroscience Methods. 2002;115(2):181-
University of Mombasa that funded this study 187.
through the Vice Chancellor, Prof. Laila 8. Wang F, Chen X, Men A, Zhang L, Wu S.
Abubakur. They also acknowledge the support Carrier frequency offset estimation for FM
received from the Partnerships, Research and and symbiotic FM radio data system hybrid
Innovation (PRI) of the Technical University of signal. China Communications.
Mombasa through Dr. Michael J. Saulo, who 2020;17(1):129-139.
guided this study, Dr. Eric Ouma Jobunga, the 9. Bossy B, Kryszkiewicz P, Bogucka H.
Chairperson of the Department of Mathematics Flexible Brain-Inspired Communication in
and Physics and the Physics academic staff. Massive Wireless Networks. Sensors.
2020;20(6):1587.
COMPETING INTERESTS 10. Prabu S, Hancock PJ, Zhang X, Tingay SJ.
The development of non-coherent passive
Authors have declared that no competing radar techniques for space situational
interests exist. awareness with the Murchison Widefield
Array. arXiv preprint arXiv:2002.01674;
REFERENCES 2020.
11. Jouvie F, Lecointe D, Briend P, Jacquin F,
1. Uchiyama K, Guowei CHEN, Niitsu K. Nicolas E. Computation of the field
Design of fully-integrated self-powered fm radiated by a FM transmitter by means of
transmitter using on-chip photodiodes in ordinary kriging. Annals of

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 Ondieki and Orori ; Curr. J. Appl. Sci. Technol., vol. xx, no. xx, pp. xx-xx, 2022; Article no.CJAST.97073

Telecommunications-annales des 14. Deatanyah P, Menyeh A, Amoako JK,

Telecommunications. 2011;66(7) 429-443. Abavare EKK, Osei-Donkor A, Quarshie E.
12. Soltanieh N, Norouzi Y, Yang Y, Karmakar Potential exposure levels from
NC. A review of radio frequency broadcast transmitters in Ghana. Radiation
fingerprinting techniques. IEEE Journal of Protection Dosimetry. 2020;192(4):516-
Radio Frequency Identification. 525.
2020;4(3):222-233. 15. Moghavvemi M, Ismail MS, Murali B, Yang
13. Blunt SD, Jakabosky JK, Mohr CA, SS, Attaran A, Moghavvemi S.
McCormick PM, Owen JW, Ravenscroft B, Development and optimization of a
Higgins T. Principles and applications of PV/diesel hybrid supply system for remote
random FM radar waveform design. IEEE controlled commercial large scale FM
Aerospace and Electronic Systems transmitters. Energy Conversion and
Magazine. 2020;35(10):20-28. Management. 2013;75:542-551.
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