Introduction
FM radio broadcast is one of the main types of radio broadcasting. FM usually denotes frequency modulation. This frequency modulation usually takes place on VHF airwaves in a frequency range of 88 to 108 around the world except Japan and Russia. This following article shares precise information on FM radio broadcast. So, find out everything about FM radio broadcast whether its advantages or disadvantages right here.
Sources have revealed that FM radio broadcasting is very popular especially in developed areas including Europe and United States because higher sound fidelity as well as stereo broadcasting certainly became quite familiar in this format. During 1930s, Edwin H Armstrong invented FM radio. He invented it to overcome the interference problem associated with AM radio broadcasting to which is relatively immune. Going further with the details on FM radio broadcast, we come up with the point that for accommodating an audio signal in FM radio, it does not require a bandwidth of 200 kHz. What is all required is 20 kHz to 30 kHz for a narrowband FM radio broadcast or FM signal. The 200 kHz bandwidth enabled space for ±75 kHz signal deviation from the appointed frequency.
Moreover, guard bands for minimizing or eliminating adjacent channel interference. However, the greater or higher bandwidth enables to broadcast for a 15 kHz bandwidth audio signal. Meanwhile the extra unused capacity is generally used for transmitting utility acts like background music for public areas, as well as GPS auxiliary signals.
The problem of AM radio interference during nighttime was generally addressed in different way. The time when FM was first set up, the available frequencies were far greater or larger in comparison to those used for AM radio broadcast roughly around 100. Using these frequencies meant that even at far larger power, the range of a given FM radio broadcast or FM signal was much shorter, thus its market was more local than for AM radio. The reception range at night is the same as in the daytime. However, all new radios included both AM and FM tuners, FM became the dominant medium, especially in cities. Because of its greater range, AM remained more common in rural environments.
Design Background
The to be established FM station, Rockstar Radio 94.7 MHz, is
a music/news/talkradio station serving mainly in Bo. Obrero, Davao City with a power of 20 000 watts. The station's studio, as well as the transmitter, will be
assembled in the fifth floor of the College of Engineering building in the University of Southeastern Philippines. DXJC will operate 20 hours a day, from 4 o’clock in the morning until midnight, 7 days a week.
1. name
2. operating frequency
3. operating power
4. operating time
Design Concept
a.) Frequency
For the project, a frequency of 94.7 MHz is used. A channel at the middle part of Very High Frequency band is selected because it is commercially available and it is more convenient for listener’s to tune their radios.
b.) Type of Module
Since the coverage area is relatively small, Rockstar Radio will broadcast in stereo where typically there is only one microphone, one loudspeaker, or (in the
case of headphones and multiple loudspeakers) channels are fed from a common signal path. In the case of multiple microphones the paths are mixed into a single signal path at some stage. Aside from mono being less expensive
for recording and reproduction, recording is easy and only requires basic equipment.
c.) Modulating Index m=Δf/fm
where:
Δf=peak carrier frequency fm=modulating frequency for commercial FM, Δf=75kHz fm=15kHz m=75/15 m=5
d.) Bandwidth B=2(m+1)*fm
B=2(5+1)*15 kHz B=180 kHz
Guard bands: 10 kHz at both ends, therefore B=180 + 2(10)
B=200 kHz
e.) Power Amplifier
In this design, we used a Class D power amplifier. The voltage mode Class D amplifier is defined as a switching circuit that results in the generation of a
half-sinusoidal current waveform and a square voltage waveform. A series-tuned output filter passes only the fundamental frequency component to the load. Class D amplifiers suffers from losses due to a number of reasons: non-zero
saturating resistance, finite switching speed and output capacitance of the devices. Class D power amplifiers are mainly used in the HF and VHF bands,
sometimes output levels up to 1 kW. They are not preferred at the frequencies in the GHZ range, although this might change in the future, Class D operation with efficiency as high as 80% at 1GHZ has been reported. A unique aspect of
Class D is that efficiency is not degraded by the presence of reactance in the load.
f.) Antenna Polarization
Vertical polarization provides the best possible coverage for frequency modulated radio signals since most of the receivers utilize vertical antennas
and the antenna design gives maximum radiation efficiency. The implementation of vertical polarization is implemented by using a half wave dipole antenna in an array system mounted on the vertical length of the
tower with a 1 wavelength spacing between each element for maximum radiation efficiency.
The station, as well as the transmitter, will be located at the fifth floor of the College of Engineering building in the University of Southeastern Philippines.
The area of coverage will be mainly Bo. Obrero, Davao City with a land area of approximately 800,000 square meters. Below are the topographical map of Davao City and the elevation profile of Obrero, Davao City.
System of Designing
a.) Block Diagram
i. The exciter is the most important part of an FM Transmitter because the FM signal is generated at this stage. It can operate as a low power standalone transmitter. The exciter section contains carrier oscillator,
buffer amplifier, and reactance modulator.
ii. After successful FM signal generation, the signal is split before being passed into the amplifier bank. This helps us ensure a low noise
amplification and improved signal to noise ratio.
iii. The various outputs from the splitter stage were directly coupled into an amplifier. A 1 kW Class C amplifier was used for this purpose. This
provides the effective power boost needed for the transmission of the signal over a range.
iv. The combiner unit is a reciprocal of the splitter unit. It is made up to three combining stages. The first stage employs four sets of 6:1 combiners to yield four 6 kW signals. The second stage uses two sets
of 2:1 combiners to two signals of 12 kW each while the third stage combines the two 12 kW signals to yield a 24 kW output.
b.) Antenna
The antenna used in this design is an omnidirectional transmitting antenna. The antenna has a gain of 2.15 dB and an impedance of 50 ohms.
Its grounding system is composed of metal clamps. The physical height of the antenna is 143 cm. Shown below are its vertical and horizontal patterns.
Frequency of
transmission, f = 94.7 MHz
λ=c/f
=3x108/94.7x106 =3.168m
Physical antenna length, l= λ/4 =3.168/4 =0.7191m Therefore, length = 71.91 cm
Ite
m # QTY Unit Description Price Amount
1 125 Feet SAT-PAK COM RG 213 Coaxial Cable 15,266.08 15,266.08
2 2 Pcs LMR-400-75 type N male plugs and grounding 6,600.00 6,600.00 3 1 Pcs Behringer Ultramizer Audio Processor 4,400.00 4,400.00
4 2 Pcs SHURE SM57 4,356.00 4,356.00
5 1 Pcs Altec Lansing VS2621 Speakers 2,350.00 2,350.00
6 2 Pcs Techno Tamashi TH-1049 599.00 599.00
7 1 Pcs ALTO Equalizer 31 band mono 4,500.00 4,500.00
8 1 Pcs MICKLE MT7-USB Mixing Console 4,999.00 4,999.00
9 1 Set BNC Connectors and Peripherals 20, 000.00 20, 000.00
10 1 Pcs Broadcom FM Broadcast Antenna 87-108MHz 11,450.00 11,450.00
11 2 Pcs 800 ft. 10-Gauge Bare Copper Grounding Wire 8,404.00 16,808.00
12 1 Pcs Airman Welder 350 amp 9.9 Generator 250,000.00 250,000.00
13 1 Pcs HP Envy Recline 27xt 53,679.00 53,679.00
14 1 Pcs Axel Oxygen 5 Broadcast Mising Console 254,952.14 254,952.14
15 1 Pcs Armstrong FM20000T2 20 kW FM Transmitter 2692582.07 2692582.07 12 months Building Rental, Power Consumption 50,000.00 600,000.00
TOTAL AMOUNT
3,922,541.2
9
FM Tower Construction and Materials 500000 500000 FM Station Studio Construction 150,000.00 150,000.00
6 Employee Salary 12,500.00 75 000.00
Labor Cost 588,381.19
Republic of the Philippines
University of Southeastern Philippines COLLEGE OF ENGINEERING
Obrero Campus, Davao City
BROADCAST ENGINEERING AND APPLIED ACOUSTICS
Rockstar Radio
94.7 MHz
Submitted to: Engr. Joey Dela Cruz
Submitted By: Cedric D. Conol Joannacel A. Paraiso
