• Written by  José Luis Fernández Jambrina

COURSE 2017/18


In this laboratory, students have the opportunity to check practically the operation of the various electronic circuits and subsystems involved in communication systems in bandwidth channels: modulators, mixers, amplifiers, oscillators, PLLs, demodulators, etc ...

The practices are carried out on modules specifically designed for teaching purposes by ETSIT professors. On them, the students check or measure the parameters or the corresponding effects of the phenomena involved under study. Theoretical concepts such as bandwidth, quality factor, modulation index, intermodulation products, frequency deviation, distortion, coupling, etc., are displayed directly with the oscilloscope or spectrum analyzer or are easily calculated from the measurements made in the job. The spectrum analyzer allows to observe the spectrum of the signals (with and without modulation), the presence of harmonics and spurious, measure characteristics of the modulators, filtering, noise, etc. and the phenomena of coupling and tracking in a PLL.

Structure of the laboratory. Groups

The laboratory has 18 jobs plus one additional teacher. It is designed for two people, so the room per shift is 36 people (up to 38). The number of shifts is adjusted to the demand according to enrollment data. The assignment of students to the different shifts will be done through the Moodle platform during the first weeks of the semester.

The formation of couples in the different shifts and positions is done once the shifts have been formed, before the actual start of the practices. In any case, a certain flexibility is offered to be able to change shifts if there are free positions for it. This change of shift can be complete (for the entire semester) and be done at the beginning of the course or in a timely manner for a specific practice.

The laboratory classes are of maximum duration of four hours and all the practices will have a theoretical introduction in the classroom of 1h at the beginning of the same. The classroom for the theoretical introduction is the A120: from 15 to 16 hours in the afternoon shifts and from 9 to 10 hours in the morning shifts.

Throughout the course open shifts will be established for the finalization of specific sections of the different practices that could not be completed in the corresponding shift.

Memories of the practices

In this same page the pdf and doc files are available for the summaries of assemblies and measurements as well as the scripts of the different practices (theoretical introduction + laboratory manual). The student must carry a printed version of said manual to write down the results of the different sections.

The part corresponding to the script of the practice plus the corresponding test included at the end of it, conveniently filled, should be delivered to the teacher at the beginning of the next practice, one copy per laboratory position. The memory must be edited, not accepting written memories by hand on the printed empty manual.



This instrument is essential for the characterization of signals in the frequency domain. After checking the basic operation of the device, modulated signals are measured in AM, FM, broadcast signals, pulsed signals and used as a demodulator of some of them.

Additional Information

- Basic handling of the central frequency and span of the analyzer

- Measurement of bandwidth and demodulation of FM signals

- Measurement of pulsed signals and demodulation of AM signals


An I/Q modulator is used to generate AM, DBL and BLU signals. The signals in the time and frequency domain are characterized. The above signals are demodulated with an I&Q or envelope demodulator.

Using the same modulator the student will generate and characterize signals ASK, BPSK, QPSK, FSK (in the oscilloscope and the spectrum analyzer). In the modulator you will check the generation of the code, the constellation, the bandwidth of the unfiltered and filtered modulated signal. In the demodulator you will observe the effect of the channel checking the deformation of the constellation and the effect of the interference between symbols on the eye diagram.

Additional Information

I/Q Modulators (Analog Devices): typically used in Intermediate Frequency for a subsequent mixing process, although they are increasingly used as direct converters (from baseband to RF)

- Generation and measurement of AMG signals

- Generation and measurement of BLU signals

- Generation and measurement of FM signals

- Assembly for the generation of digital modulations

- Eye diagrams

- Constellations in baseband and intermediate frequency

Electric schemes


This practice is of special interest given the large field of use of oscillators engaged in phase. It compares parameters of different types of oscillators, revealing the need for a loop locked in phase. Three types of phase detectors are compared and the parameters of a PLL are measured: the transfer function (bandwidth, own frequency and damping factor), the latching and tracking range and the latching time. In addition, its operation as a frequency and phase modulator-demodulator is checked. Finally, a frequency synthesizer is mounted and the operation of its fixed and programmable dividers as well as the characteristics of the synthesizer are checked. The use of the spectrum analyzer is especially advisable in this practice.

Class presentation (pdf)

Theoretical introduction and laboratory manual (pdf)

Theoretical introduction and laboratory manual (doc)

Additional information

Commercial PLLs

Analog Devices page: Plls and full and fractional division synths. Direct Digital Synthesis (DDS)

Freescale: Application Note

Hittite: Microwave PLLs (with integrated VCO)

Altera: PLLs in FPGA

Designs ETSIT (GMR)

- Engagement and tracking margin

- PLL as an FM demodulator

- PLL as phase modulator and frequency synthesizer

Electric schemes



Here the student studies the different blocks of the transmitter, obtaining the amplitude-frequency characteristic (gain and bandwidth) of the intermediate frequency amplifier and the radio frequency amplifier. It also checks the correct operation of the local oscillator and the frequency converter.

In addition, the characteristics of the receiver are determined: sensitivity (noise figure), selectivity, pass band, rejection of the image signal and the IF signal. The operating margin of the CAG is also measured and the operation of the transmitter-receiver set (transceiver) is checked.

Class presentation Summary of assemblies (pdf).

Theoretical introduction and laboratory manual (pdf).

Theoretical and manual laboratory introduction (doc).

Additional information


UP-CONVERTER tipical. TEXAS instruments

UP-CONVERTER. Development kit. Nuwaves Engineering

Designs ETSIT (GMR)

- Amplitude response of a subsystem

- Spectral components at the output of a mixer

- Automatic gain control

- MDS. Measurement of noise figure

Electric schemes

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