3.3 Terminal radio relay station (trs)

The signal is amplified and corrected in adapter unit. The separation filter excludes the effect of the transmission path on the receiving path.

IFA – intermediate frequency amplifier; AL-amplitude limiter; HPIFA – high power IFA; RG – reference generator; BF-band-pass filter; PA-power amplifier; AGC-automatic gain control; QAM-quadrature amplitude modulator.

Figure 3.3 – Functional scheme of transmitter

As a modulated signal the harmonic oscillations with frequencies =35 MHz, 70 MHz, 108 MHz, 140 MHz, 575 MHz, 1 GHz are used. They are called intermediate frequencies. Through the quadrature amplitude modulator the signal is transferred to the intermediate frequency range. Choose the so that from this row (or if GHz):

=24,8 GHz

An intermediate frequency amplifier performs the main amplification. The amplitude limiter eliminates residual amplitude deviation, introduced by intermediate frequency amplifier. Then the signal enters high power IFA, which provides the desired signal power. Then, here is a mixer: modulator and band-pass filter that form a single sideband. Reference generator is a heterodyne

path, which forms a carrier frequency. A mixer transfers the signal into SHF range thatis amplified and transmitted into antenna-feeder path. The intermediate frequency range allows constructing an amplifier with high linearity of amplitude characteristic, small band pass flatness (irregularity of frequency response) and obtain high amplification that cannotbe obtained in the SHF range. Besides, intermediate frequency usage allows unifying the part of equipment.

AA-auxiliary amplifier; FD-frequency detector; LPF –low pass filter; IFPA –intermediate frequency power amplifier.

Figure 3.4 – The functional scheme of receiver

The band-pass filter at the input of reception path eliminates the influence of neighboring trunks. Frequency transformer (modulator and filter) transfers a signal to intermediate frequency range. There are intermediate frequency power amplifier (performed as low-noise amplifier) and intermediate frequency amplifier. An automatic gain control is performed in a feedback circuit of the intermediate frequency amplifier as a method of fading control. The amplitude limiter eliminates residual amplitude deviation. The deep limitation is used. Frequency detector demodulates the signal. And then the signal enters an auxiliary amplifier.

3.4 Intermediate radio relay station (irs)

SHFRG – super high frequency generator; PA-power amplifier.

Figure 3.6 – The functional scheme of IRS-1

Radio retransmitters are installed at intermediate stations between transmitting and receiving antennas in order to compensate the SHF signals attenuation during their transmission in the free air.

GHz

FIBER OPTICAL COMMUNICATION SYSTEM WITH DWDM IN THE RING