Panels made in metal case with bench support and the electrical scheme on the front panel.
The board must consist of FSK (Frequency Shift Keying) modulator and demodulator sections that can be interconnected in order to simulate a complete transmission system.

Technical Features:

• The board must use the support board as a service module to provide the carrier signal, the modulating random digital signal, the error rate meter and the line simulator. FSK modulator and PLL demodulator.
• The panel must contain:
• NRZ encoder: it must encode the TTL level signal coming from the auxiliary generator into signals having bipolar NRZ line code.
• Duo-binary encoder: it will be used to study the operation of the FSK partial response transmission system.
• FM generator/modulator: it must be able to operate with digital modulating signals. The modulation index will be variable by means of a suitable drive (MODULATION).
• Receiver: it must be composed of an intermediate frequency amplifier (IF).
• FM demodulator: it must be of the PLL type, followed by a low-pass filter.
• NRZ decoder: it must accept in input the signal produced from the demodulator and it shall operate in base to a timing generated in the receiver from the clock regenerator. The NRZ decoder shall be equipped with a variable decision threshold used internally to distinguish between the logic levels of the received signal.
• Duo-binary decoder: it must allow to study the operation of the partial response FSK system. The circuit shall use the clock provided by the regenerator circuit of the receiving section and it is equipped with a manual drive to determine the level recognition thresholds.
• Reception clock regenerator: this module must simulate the extraction and regeneration circuit of the timing signal present in the receiving terminal of any data transmission system. The clock regenerator shall be composed by a PLL (Phase Locked Loop) which can be synchronized with the transitions of the received signal. For its nature, the circuit can synchronize with the frequency of the clock used for the transmission and also with its harmonics and sub-harmonics. To make the educational use easier, this regenerator clock must be equipped with a manual check of the PLL (f ADJ) free oscillation frequency, so that the PLL itself will be carried manually to lock to the fundamental frequency of the transmission clock.

For an immediate verification of the right lock, the regenerator must be  equipped with a Led (LOCK) that switches on when the regenerated clock coincides with the transmission one. In default of this signalling device it is necessary to display the two clocks (transmitted and regenerated) on the oscilloscope.
The clock regenerator shall be equipped with a phase shifter allowing to dephase the (rise) active edge of the clock of about 180 degrees, for especial test purposes.
It will be possible to notice that, if we change the bit rate (transmission speed or transmission clock frequency) it will be necessary to adjust again both the PLL free frequency, for the lock to the new frequency, and the regenerated clock phase, to reset the receiver operation.
With this board it must be possible to perform the following experiments:

• FSK systems architecture
• FSK modulation/demodulation procedure
• Error rate measurement as a function of different transmission speed and of the characteristics of imperfect transmission media (attenuation, noise).
• Operation of the panel
• FSK system with NRZ line code
• Partial response FSK system with duo-binary coding
• FSK system with NRZ code in presence of transmission noises
• Partial response FSK system with duo-binary coding in presence of transmission noises