AASCIT Journal of Physics 2017; 3(4): 18-27 http://www.aascit.org/journal/physics ISSN: 2381-1358 (Print); ISSN: 2381-1366 (Online)

Development of Am Field Strength Meter

Babalola Micheal Toluwase 1, * , Akeredolu Bunmi Jacob 2, *, Ewetumo Theophilus 3

1Department of Physics, Afe Babalola University, Ado Ekiti, Nigeria 2Department of Pure and Applied Physics, Federal University, Wukari, Nigeria 3Department of Physics Federal University of Technology, Akure, Nigeria Email address

[email protected] (A. B. Jacob) * Corresponding author Citation Keywords Babalola Micheal Toluwase, Akeredolu Bunmi Jacob, Ewetumo Theophilus. Development of Am Balanced Full-Wave Detector, Field Strength Meter. AASCIT Journal of Physics. Vol. 3, No. 4, 2017, pp. 18-27. Micro Controller, Demodulation, Abstract Phase Locked Loop The Amplitude Modulated field strength meter circuit consists of an antenna, AM demodulation unit with signal indicator output, tuning circuit comprising of a phase lock loop (PLL), integrator, differential amplifier, frequency divider, microcontroller output with serial communication interface and a varactor. The AM demodulator IC uses Received: April 29, 2017 balanced full-wave detector method for demodulation. Internally, it has a full wave Accepted: July 30, 2017 rectifier circuit that gives signal strength indication output, and frequency oscillation that Published: September 20, 2017 can give audio output as well. The output signal is fed into an analogue to digital converter (ADC) of a microcontroller (PIC 16F877) to display the measured value. This system will display the frequency received by dividing the frequency from the oscillator, and this will be fed into PIC16F877 to give station frequencies that will be locked into. To be able to confirm the stations, an audio output is incorporated so that the station programmes can be heard. Tuning to different stations is done using PLL circuit which generates a local oscillation via a varactor for balanced full-wave demodulation. The system is equipped with facility to interface with computer via comport using visual studio2008.net program to store the data at every two seconds time interval.

1. Introduction Communicating over long distances has been a challenge throughout history. In ancient times, runners were used to carry important messages between rulers or other important people. Modern telecommunications began in the 1800s with the discovery that electricity can be used to transmit a signal. For the first time, a signal could be sent faster than any other mode of communication e.g. transportation. Yet there are many challenges which face the so called modern communication system, such as a barrier that reflects the signal away from reaching the targeted audience. More importantly the strength of signal transmission which conveys information to people varies with the time of the day because of topography and weather [1]. Addressing this problem leads to development of monitoring equipment to express the quality or value of a particular signal strength at a certain distance from its transmission station [29]. The paper will assist in the development of field strength meter. In Telecommunications, a field strength meter is a measuring device which measures the intensity of the electric field caused by a transmitter. A field strength meter in its simplest form is a simple radio receiver. The tuner circuit is at the front end; then the 19 Babalola Micheal Toluwase et al. : Development of Am Field Strength Meter

signal is detected and fed to a micro-ammeter, which is the transmitter power output in watts and d is the distance scaled in dBųv [29]. The frequency range of the tuner is from the radiator in metre. usually within the terrestrial broadcasting bands, though Field intensity measurements are made in support of a some field strength meters can also receive signals in the reference. Section 12.4.2.1 of the Nigeria broadcasting code gigahertz range. In an ideal free space, the electric field NBC [22] specifies that a broadcaster shall maintain strength produced by a transmitter with isotropic radiation is specified minimum values of field strength within its readily calculated as [27] assigned coverage area depending on its mode of transmission and its location’. Accordingly, the acceptable E= √ (1) minimum values shall be as indicated in table 1: where E is the electric field strength in volts per meter, P is Table 1. The acceptable minimum values of field strength within assigned coverage area in Nigeria.

Urban Areas microvolt/m Rural Areas i. AM Sound Broadcasting 72 dB i. AM Sound Broadcasting 66 dB ii. VHF-FM Sound Broadcasting 60dB ii. VHF-FM Sound Broadcasting 48dB iii. VHF-Television (Band III) 60dB iii. VHF-Television (Band III) 49dB iv. UHF-Television (Band IV) 65dB iv. UHF-Television (Band IV) 60dB v. UHF- Television (Band V) 70dB v. UHF- Television (Band V) 60dB

The AM field strength meter measures the strength level of a in figure 1. It works as follows. An antenna A 1 intercepts an signal that is being received from any AM transmitter. It detects AM radio wave and supplies the signal to a radio frequency the electric field of AM radio frequency (RF) signals. The meter amplifier S 1 of a receiver chip U 0. The radio wave is reads the signal strength directly on the display [3, 17, 29]. To amplified by the RF amplifier S 1 and is fed to a mixer S 2 design sensible and sensitive AM field strength meter, it is together with oscillator signal from controlled oscillator S 3. useful to understand the amplitude modulation process. The controlled oscillator signals is generated from frequency Amplitude modulation (AM) occurs when the amplitude of synthesiser and fed into the mixer; multiplicative mixing a carrier wave is modulated, i.e the process of impressing a occurs between the AM rf input and oscillator signals. The low frequency intelligent signal into a high frequency carrier mixer output provides the intermediate frequency (IF) at pin signal [19], and it has an equation of the form: 1 of the receiver U 0. The output signal from IF filter is fed to IF amplifier via pin 3. The output signals from IF amplifier = [ + (t)] cos2 t+ ∅ ) (2) S4 is internally fed to the balance full-wave detector S 5. The balanced full-wave detector demodulates an audio signal where the modulating signal component (t) is added to the which corresponds to a modulated broadcast signal. The carrier amplitude , then the modulated carrier wave is detected audio frequency output is passed through an AF pre- , the term [ + (t)] describes the envelope of the amplifier S to audio amplifier S through pin 6. modulated wave. The frequency is the frequency of the 6 7 The Local oscillator signal from the local oscillator S via carrier while ∅ is its phase [12]. A device that performs 3 modulation is known as a modulator and a device that pin 10 of AM receiver U 0 is fed to comparator and inverter performs the inverse operation of a modulator is known as a which convert the sine wave to square wave before input to demodulator (sometimes detector or demodulator). A device programmable divider U 4. The divider divides the frequency that can do both operations is a modem. [2]. An AM receiver fx of the channel signal with a predetermined ratio N. The detects amplitude variations in the radio waves at a particular new signal is fed to a phase detector of PLL U 19 which is frequency. It then amplifies changes in the signal voltage to supplied further with the reference signal from reference drive a loudspeaker or earphones [28]. A perfect AM oscillator U 21 . The detector compares the frequency divided transmitter, modulated with a single sine wave tone would signal with the reference signal and produces a signal which radiate a constant average power regardless of modulation represents the frequency difference and/or phase difference. level, with spectral power shared among the assigned The signal has its ripple component removed by a low pass frequency carrier and two sideband frequencies above and filter (LPF), and is therefore amplified into a control signal. below the assigned centre frequency by the frequency of the The DC voltage level of the control signal is supplied to the modulating tone. A field strength meter, or calibrated power local oscillator S 3. The oscillation frequency of the local bolometer, would read a constant value, with or without a oscillator is changed according to the voltage level of the modulating tone [17] control signal. The local oscillator S 3 is therefore called "voltage controlled oscillator (VCO)". The signal from a 2. Method field strength indicator is amplified and fed through the microcontroller to the display. The control key input the 2.1. Basic Description of the Block Diagram frequency of the channel station, and both the field strength The block diagram of an AM field strength meter is shown readings and the frequency of channel station are displayed AASCIT Journal of Physics 2017; 3(4): 18-27 20

on the LCD. The audio signal is taken from pin 6 of U 1 and re-amplifies before it is fed to the speaker.

Figure 1. Block diagram of AM Field Strength Meter.

2.2. Circuit Description Very good cross-modulation behaviour is also achieved by AGC delays at the various signal stages. Low noise working The circuit in figure 3 can conveniently be divided into is achieved in the differential amplifier by using transistors three parts; the AM receiver circuit, frequency synthesizer with a low base resistance. A double balanced mixer provides circuit and controller circuit. the IF output at pin 1 of TDA1072. Local oscillator operates 2.2.1. Receiver Circuit at 455kHz above the wanted incoming signal frequency i.e if The sensing unit (antenna) used, was a monopole antenna the wanted signal RF is 1000kHz, then the local oscillator of 50 ohms, which was capable to intercept or capture a radio frequency will be 1455kHZ. The oscillation frequency is wave travelling through space and able to deliver them to a generated by a frequency synthesizer with varactor D1, and a receivers. Other features of the antenna include its length, parallel tank (made up of coil L1, and capacitor C20 and C2) power received and antenna factor, made it an ideal choice connected between pins 11 and 12 of IC TDA1072. The local for this project. The main component of the receiver is a oscillator needs to be tuned to a range 990 to 2100 kHz, such TDA1572 AM receiver chip U, around which everything else that, it’s frequency plus the IF frequency (455 kHz) equals was based, TDA1572T is a 16-lead mini pack plastic package, the received frequency, that is a range of 990 to 2100kHz. i.e normally measuring and yet it contains 10 major circuit from (535 + 455 to 1645 + 455kHz). A varactor diode D1 blocks, these blocks are integrated on a chip. TDA 1572T which gives about 90 to 200pF along with the capacitor C21 performs all the main function of an AM superhet radio set the tuning span and the tank inductor L1 of 95 , formed receiver including RF Amplifier, Local Oscillator, Mixer, by a copper wire wound round a ferrite core. Extra oscillator Detector, AF Amplifier, AGC system and Field strength output from pin 10 of IC TDA1072 is fed to programmable indicator. The captured signal from an antenna is fed to pin divider through transistors Q1 and Q2 and a comparator U32 14 of RF amplifier via capacitor C23. The differential which are used to amplify and convert the analogue signals amplifier in the RF stage of TDA 1572T employs an AGC (sine wave) to digital (Square wave) to form input signal to negative feedback network to provide a wide dynamic range. programmable divide The intermediate frequency signal from 21 Babalola Micheal Toluwase et al. : Development of Am Field Strength Meter

the mixer output via pin1 of TDA 1072 is filtered through IF processing unit. It is a complete computer on a chip, and filter. Designing of IF filter was done using the formula, entire processor, memory and the I/O interfaces are located on a single piece of silicon. For this reason, it takes less time 1 = (3) to read and write to external devices. Pic16f877 U1 has three 2√ types of memories which are: flash program memory, Where is the centre frequency, L is the inductor and C is Electrical erasable memory and static random access memory. the capacitor. Pic16f877 is also has 33 inputs and output pins that can be Since 455kHz was selected as centre frequency, the IF individually configured as inputs or outputs filter, FL1, consists of two pole ladder crystal filter X3 and These ports have been assigned to the various tasks in the X4 of 455kHz, a matching transformer TR1, capacitors C28 circuit; and C29. The matching transformer has 13 turns on the PORTA bit 0 is configured via firmware as an analogue primary coil and 9 on the secondary coil of TR2. A trimmer input for analogue to digital conversion. One channel is used capacitor C50 is used to resonate the inductance of 31 H of in this project to convert received signal strength from pin 9 the primary coil of TR1. of TDA1572T, in analogue form to digital, which will be 1 C29 can be calculated as follows: = , the then be displayed on the LCD unit, 2√ PORTC bits 6 and 7 were used as transmit and receive pin value of C29 is given as; = 3.9 for asynchronous communication with a user PC (personal The TR1 and C29 are used to tune to 455 kHz, giving a computer) using RS232. PORTA bits 1, 2, 3, 4, 5 and good match for IF filter: a 2 pole ladder filter is from toko. PORTE bit 2 are used for the user keypad. Each of these pins Inside the TDA 1572T the full- wave balanced envelop was configured as inputs. A 10 kΩ (R1 to R6) pull-up detector is used for demodulation of the intermediate resistor was used for each pin, while a de-bounced button frequency to audio frequency signal, internally it has a low serves as the keypad. Via firmware the PIC monitors the state pass filter to block residual IF carrier from signal path. The of each pin. When not depressed the PIC sees logic 1 and audio frequency signal is amplified by AF pre-amplifier, does nothing and when depressed the PIC sees logic 0 and which uses an emitter follower with a series resistor (inside performs the associated routine attached to it. The keypad the TDA1072), together with an external capacitors, provides allows channel selection from 500 kHz to 1699 kHz. the required low-pass filtering for AF signals. The audio PORTB and the lower 4 bits of PORTC were configured filter at pin 6 of TDA1072 consisting of the capacitor C27, as output and were used to give data for the programmable C26 and resistor R33. The AF output voltage at input signal divider used in the frequency synthesizer 50 is 130mV, (Data sheet TDA 1072) so there will be PICs generally have internal oscillator buffer configuration need for amplification, because a normal audio line is 0.5 to option. In the circuit design, the HS (high speed crystal) 2 Volts. (Kennick, 2001). LM 386 is used to amplify the option is used with a 16 MHz crystal X1, because 16 MHz audio signal before fed to speaker. crystals are widely available in the market. Also the circuit The AGC amplifier provides a control voltage which is clock is the time base for the generation of the serial proportional to the carrier amplitude. Second-order filtering communication baud rate with the PC of the AGC voltage achieves signals with very little distortion, even at low audio frequencies. The AGC voltage 2.2.3. Frequency Synthesizer is fed to the RF and IF stages via suitable AGC delays. A frequency synthesizer is a circuit design that generate a The data sheet of IC TDA 1072 has a graph of field new frequency from a single stable reference frequency. For strength voltage indicator in volts against RF input signal in frequency span 535 KHz to 1605 KHz, the standard divide dBµV, this graph has good linearity for logarithmic input by N value and a fixed divide by M value of 2 are used. signals over the whole dynamic range. A buffered voltage Since N needs to be between 535 and 1605, The ICs required source from the IC TDA 1072 provides a high-level field for the programmable divider is LS74161. The LS74161 is a strength output signal. At maximum voltage of 28V, the 4 bit synchronous, pre-settable counter. This counter is fully corresponding RF input is 120dB µ and this was used in programmable; the output may be preset to logic 0 or to calibrating the field strength of the received signal. Philips logic1. Pre-setting is synchronous. To achieve the semiconductors (1989) programmability from 990 to 2060 for this work a 12 bit counter is needed. Three LS74161 (U33, U32 and U31) are 2.2.2. Controller Circuit with User Input and cascaded to make a 12 bit counter. The output from the VCO Output Interface (Microcontroller) and is coupled to the programmable counter via a 2.2uf capacitor LCD C7 and converted to square wave using the 7414 Schmitt The pic16f877 is a controller used in this paper. It is an 8 trigger NOT gate U34. bit RISC (reduced instruction set computer), central

AASCIT Journal of Physics 2017; 3(4): 18-27 22

Figure 2. Block diagram of frequency synthesizer.

The reference oscillator is 500 Hz, A crystal oscillator of 8 Where R F is 2.2 kilo-ohms (R 17 ) and 1 kilo-ohms (R V2 ) MHz, X2 was obtained and divided down to 500 Hz. The variable in series circuit is shown in figure 2. The NOT gate 7404, (U15, U16 R18 is 10 kilo ohms, Therefore, and U34) serves as amplifier (buffer) for the crystal to 2.2 1 = 1 3.2 = 1.325 oscillate and the two 1kΩ resistors (R9 and R10) are the 1 10 10 feedback resistors for the amplifier. LS74161, a 4 bit counter divides 8 MHz, X2 by 16 to get 500 kHz, Also three 4017 This gives a gain of less than 2 decade counters (U21, U22 and U23) are cascaded to form a 2.2.5. Audio Amplifier divide by 1000 counter, the result is that 500 KHz is divided The LM386 is a power amplifier designed for use in low by 1000 to get 500 Hz, on pins 12 of the 3 rd 4017, U38 voltage consumer applications. The gain is internally set to 2.2.4. Phase Locked Loop 20 to keep external part count low, but the addition of an The integrated circuit CD4046, U36 is the phase locked external resistor and capacitor between pins 1 and 8 will loop used in the circuit. The reference oscillator output signal increase the gain to any value from 20 to 200. The inputs are of 500Hz is fed on phase comparator II of PLL. The output ground referenced while the output automatically biases to of VCO (from TDA1572T receiver) is fed back to the phase one-half the supply voltage. The quiescent power drain is comparator II second input, through a programmable divider only 24 milli-watts when operating from a 6 volt supply, that has been programmed to divide by any number from 990 making the LM386 ideal for battery operation. to 2100. The loop will lock when the frequency fed back 2.2.6. RS232 Serial Port through programmable divider is equal to 500Hz of reference Serial Ports come in two sizes; there are D-Type 25 pin oscillator frequency. A simple RC filter is employed as the connector and the D Type 9 pin connector both of which are loop filter. Where C12 is fixed at 1000µf, the value of R male on the back of the PC, thus you will require a female varies via a digital switch between 10 kΩ, 100 kΩ and 330 connector on your device. RS-232 communication is kΩ. The CD4066 analogue switch is controlled by the PIC asynchronous, a clock signal is not sent with the data. Each controller. The need for using different loop is to ensure fast word is synchronized using its start bit, and an internal clock lock and smooth lock. The centre frequency of the low pass on each side, keeps tabs on the timing. The first step in filter is given as connecting a device to the RS-232 port is to transform the 1 RS-232 levels back into 0 and 5 Volts. This is done by RS- = (4) 2 232 Level Converters. An example of such a device is the This gives a frequency cut-off of 0.015Hz for R = 10 kΩ, MAX-232 use in this work. 0.0015Hz for R = 100 kΩ and 0.00048Hz for 330 kΩ. The 2.2.7. Power Supply output of the phase comparator/detector is amplified using The circuit is powered from an 18 volts rechargeable LM 741 OP-AMP. A non-inverting amplifier configuration is battery source. A transformer is provided to charge the used. The gain of the stage is; battery. The voltage is then regulated to 12 volts and 5 volts for each stage using voltage regulator 7805 . 1 (5)

23 Babalola Micheal Toluwase et al. : Development of Am Field Strength Meter

Figure 3. Complete Circuit Diagram of AM Field strength meter.

A firmware program was developed to test the working of this circuit, below is the flow chart used. AASCIT Journal of Physics 2017; 3(4): 18-27 24

Figure 4. Flow Chart for the Microcontroller.

Figure 5. PC graphic user interface.

Plate 1. Real-Time Data Logging with Laptop. 25 Babalola Micheal Toluwase et al. : Development of Am Field Strength Meter

The flow chart is then converted to the source codes using from abroad ranges from N100,000.00 to N300,000.00 ($280 ASSEMBLY program. The Real-Time Data Logging with to $840), the rate of conversion was $1 to N360. This clearly Laptop is shown in plate 1. The PIC programmer is used to indicates that the newly developed FSM is cheaper since part “burn” the source codes into the PIC. The serial port program were sourced locally. Table 2 shows the cost analysis of the is written using visual basic dot net 2008 edition. This field strength meter. program reads the serial port data and displays in a text box with the TIME information shown in figure 5. The complete Table 2. Cost analysis of FSM. work is shown in plate 2 Materials Quantity Cost (N) Cost ($) AM receiver 1 2,000 6.0 Battery 3 2,400 7.0 Transformer/ crystal Oscillators 1 1,200 3.3 PIC 16f877. Microcotroller 1 1,000 3.0 Other components 20,000 56.0 Casing 1 3,000 8.0 Transportation 3,000 8.0 Total N35,000 $91.30

3.3. Testing of Am Field Strength Meter

On completion of the design and construction work, certain performance tests were carried out with the meter and the available one (imported field strength meter lag-gear, model TC805C) from the Electrical Engineering Department, University of Ibadan in Ibadan, Oyo State. The test took place in five different locations in Ibadan; the two Plate 2. Complete work of FSM. instruments were used to measure the AM field strength from AM transmitter of the Broadcasting Corporation of Oyo State in Ile Akede, Bashorun, Ibadan, transmitting at the frequency 3. Operation and Performance of the of 756kHz. System 4. Result and Discussion 3.1. Calibration of the Field Strength Meter The constructed meter performance was evaluated in terms The AM field strength meter was calibrated against a of sensitivity and against standard imported FSM. Figure 6 laboratory standard. The calibration was made to prove the shows the result of the field strength values in decibel- performance of the equipment after the construction. The microvolt against distance of various locations meter was also calibrated with the standard and imported where the measurement took place in kilometres (km) for field strength meter lag-gear, model. TC805C. The two two meters (imported and constructed FSM). It was observed meters were used together for measurement at the same time that, as the two meters were moving away from the at different locations in Ibadan Oyo state. Before the transmitter in kilometres, there was gradual decreased in the measurement the two meters were switched on, the field strength measurements. At Bodija market located 2.9m constructed meter was adjusted to give the same reading with away from Akede AM Transmission station, the variation the standard meter at initial reading of 30dBµV before tuning percentage in the values of the two meters was about 0.1%. to the station. On tuning the two meters to the AM broadcast Also at UI (5.8km away), the variation percentage in the two transmitting station, broadcasting at frequency of 756 kHz, meters was 0.05%, at N. B (7.0km away) the variation in the readings were recorded for five different locations. The result values of the two meters was 0.001%. But at Ibadan airport shown in figure 6, gives 95% accuracy with imported Model (8.0km away) and IITA (10km away) there were no TC805C. significant variations in the value recorded in the two meters, 3.2. Cost Analysis i.e the meters read the same value in decibel-microvolt ((dBµV)). The variations in values of the FSM measurement One of the advantages of using the newly constructed AM of the two meters were as a result of minor errors that might field strength meter is cost efficiency of the meter. By occur during the development of the constructed meter. analysing the cost of the constructed AM field strength meter, the total cost is N35,000.00 ($175), but the minimum cost of acquiring a field strength meter of the same frequency range

AASCIT Journal of Physics 2017; 3(4): 18-27 26

Figure 6. Graph of field strength (dBµV) against distance (Km).

specify with accuracy of 99% 5. Conclusion Hence, the use of this system is limited to area where AM An AM field strength meter capable of measuring AM Transmission is available signals from any AM broadcasting transmitters with centre frequency of 500kHz to 1650kHz, bandwidth of 10khz and References gain control from 0 – 120dBµV was designed, constructed [1] Ajileye, O. O, Jegede, O. O, Ayoola, M. A, Eguaroje, O. E and tested. The system consist of an antenna, AM and Mohammed, S. O (2014). Variations of Surface demodulation unit with signal indicator output, pre-amplifier, Refractivity for Different Climatic Zones across West Africa, frequency divider, tuning circuit comprising of a phase lock International Journal of Scientific & Engineering Research, loop (PLL), integrator, differential amplifier, microcontroller Volume 5, Issue 3, 521 ISSN 2229-5518. output with serial communication interface and a varactor. [2] Aru, O. E, Anorue, E and Nwaokafor, N. K. C (2014). Design The AM field strength meter integrates a digital tuning using and Construction of a Simple but Efficient and Cost Effective frequency synthesisers, and data logger for interface with a Amplitude Modulated Transmitter Using Locally Available computer. Frequency synthesiser helps to overcome some Material. International Journal of Engineering Trends and problem of accuracy and stability of signals. Technology (IJETT) – Volume 8 Number 7. A comparison test was conducted with this meter using the [3] Andrews J. K. (2006): Calibrating a Low Frequency Field signal level meter, lag-gear, model TC805C as a standard Strength Meter, W1TAG, November, accessed 23 rd of October meter. The work testing exercise was conducted in five 2013. www.w1tag.com/FSM_CAL.pdf. different locations in Ibadan city, Oyo State. Comparing the [4] Behzad R, (1996); RF Microelectronics, Prentice-Hall, fifth readings of the two meters (imported and constructed FSM), edition. the result shows that the constructed field strength meter was 27 Babalola Micheal Toluwase et al. : Development of Am Field Strength Meter

[5] Bela. L (2002): Instrument engineers’ handbook: Process [19] Mohamad F. H, Mohamad H. J, Ahmad A. S (2015), Software and Digital Network. CRC Press New York. Pp 343. Readability of Amplitude Modulation (AM) Transmitter and Receiver Laboratory Manual. International Journal of [6] Best, R. L (1997). Phase Locked Loops, Design Simulation Innovative and Emerging Research in Engineering Volume 2, rd and Application, 3 Edition, McGraw-Hill. Issue 5. [7] Bray. J (2002). Innovation and Communication Revolution; [20] More C. T, Sharma A. K, Bhonsle R. V, Kenneth J. W. L from the victorian pioneer to broadband internet. Institute of (2010). Field strength measurement of VLF Radio wave electrical engineers. pp 59, 61-62 ISBN 0852962185. propagation at 19.8kHz between Australia and India. Proceedings of the 10 th Australian space science Conference, [8] Carusone, T. C, Johns. D. A, Martins. W. K, (1989), Analog nd 2010. National space society of Australian Ltd. ISBN 13; Integrated Circuit Design, 2 edition John Willey & Sons Inc 978,0.9775740-49. ISBN 0-471-14448-7. [21] Newkirk, D. and Kerlquist. R (2004). Mixer Modulator in D. [9] Doeblin E. O (1969). Measurement system, application and G Reed (ed). The ARRL. (81 st ed) ISBN 0-87259-196-4. design. McGraw Hill publishing company. New York. Newington [10] Dufff, W. G (1976). A hand book on mobile communications. [22] Nigeria Broadcasting Code (2010), 5th Edition Don white consultants. Inc. Warrenton Virginia. [23] Pejza. F. J (1972). A beginner’s guide to the ionosphere DX [11] Elimbinber J (1990). Designing with linear integrated circuits, monitor, international radio club of America. John willy and sons. Inc. New York. Pg 13-31. [24] Philips semiconductors (1989). TDA1072 AM receiver circuit, [12] Godse A. P and Bachi V. A (2009). Communication product specification file under integrated circuits, IC01 Engineering. Technical publications p. 36-38. ISBN 978-81- 8431-089-4. [25] Ranjana Singh, Nidhi (2013). Design and Working of FM Transmitter, International Journal Of Advance Research In [13] Gray L and Graham R. (1961). Radio Transmitters. McGraw Science And Engineering http://www.ijarse.com IJARSE, Vol. Hill publisher pg. 141. No. 2, Issue No. 10, October 2013 ISSN-2319-8354 (E).

[14] Hall D. V (1989). Digital circuits and systems. McGraw-Hill [26] Reehal. G (2002) A digital frequency synthesizer using Phase publishing company, New York. ISBN 0-07-025537-7. locked loop techniques, Degree Master of Science in the [15] Harris, D. M and Harris. S (2012): Digital Design and Graduate School of the Ohio State University. Computer Architecture. Morgan Kaufmann Inc. ISBN 978-0- [27] Robert B and Louis N. (1996). Electronics Devices and 12-394424-5 pp. 79. Circuit theory Prentice- Hall international Inc. New Jersey pg [16] Jain R. K (2004). Mechanical and industrial Measurements 819-879. process instrumentation and control Khana Publishers. India [28] Sams, H. W. (1977): Reference Data for Radio Engineers, 6 th pg 198-200. Edition, Howard W Sams & Co Indianapolis ISBN 10: 0-672- [17] James V. N.(1975), AM Field strength measurement (540 – 21218-8, p 27-47. th 1600kHZ), NAB engineering handbook, 6 edition. Vir. [29] Shiv Kumar Singh (2016). Study of Amplitude Modulation James consulting radio engineers, Denver Corolado. Pp 387 - Transmitter, International Journal on Recent and Innovation 409. Trends in Computing and Communication ISSN: 2321-8169 [18] Kennedy N. (2002), The One-Chip Receiver, A 7 MHz CW Volume: 4 Issue: 11: 28-33. Receiver Using The TDA1072 CHIP. www. th [30] Wikipedia, the free encyclopaedia: Field Strength meter, suddenlink.net/wa5bdu/1chiprx.htm. accessed 12 October www.en.wikipedia.org/wiki/field strength meter 2016.