Delivery in day(s): 4
Part I Specify the functional specification and
Specify the functional specification and design using different FM radio frequency channels from 88MHz and 108MHz.
The overall FM repeater system explanation and its function
The FM radio is a terrestrial communication system that transmits the radio waves on land. The transmission is done at the broadcasting station where the information or the message signal is encoded and transmitted within a band limited frequency. The system, thereafter, encodes the signal using matching x-former and transmits it through the antenna. The antenna is placed on a tower which is of great length depending on the distance it is meant to project the signal. The antenna is set to have a specific power and gain value which determines the distance a signal will travel before it loses most of its energy. There are two sections of the FM radio: the transmitter end and the receiver end. These two perform the encoding and decoding of message signals respectively. In a practical case, the signal is transmitted by a broadcasting radio station or a telecommunication company and an user equipment or a mobile equipment such as a cell phone or radio gadget receives the signals and processes them to get the transmitted message. The FM radio repeater system has several components that constitute the transmitter and the receiver.
FM transmitter block
The transmitter is the initial component in the wireless media communication link design. The transmitter takes the encoded message and modifies the AC signal using a modulation technique. The generated carrier signal is transported either directly to the antenna or through a cable to the antenna. The transmitter determines the amplitude or the power level of the signal for transmission. The higher the amplitude of the wave, the more powerful the wave and the further it will travel. The power levels that the transmitter is allowed to generate are determined by the local regulatory bodies such as the FCC in the USA. In this project, the FM range provided is
RF Bandpass filter
FM receiver block
RF Bandpass filter
The digital up-converter is comprised of the following DUC cascaded objects of three interpolation filters and an oscillator that up converts the interpolated signal to a specified pass-band frequency.
Band-pass filter design
Input matching network (IMN) design using smith chart
RF power amplifier design
Output matching network (OMN) design using smith chart
Antenna-matching quarter wavelength transformer
Power budget calculation from output of mixer to transmit antenna chain
FSPL and link budget from the transmit antenna to the receiver input calculation
During transmission, the radio waves encounter a lot of losses due to climatic conditions, land features, and other forms of interference. Signal power diminishes during transmission due to the geometric spreading of the wave front, hence, the free space loss. Geometric spreading happens because the wave front radiated signal energy expands as a function of the distance from the transmitter.
Figure 1 Tx to Rx link via Radio waves [source: Dr. Tahseen Al-Doori]
The link budget quantifies the communication link performance.
Consideration for parasitic/stray capacitance/inductance, PCB board layout considerations, practical component values selection.
Final complete circuit design with components values specified from output of the up-converter mixer to the transmit antenna.