Cable AML ITX21-100, Руководство по установке и обслуживанию

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Indoor Broadband Transmitter – ITX21-100
IM4030013-1 Rev –
7
2.0 CIRCUIT DESCRIPTION
The ITX21-100Transmitter consists of the following circuits or modules:
1. Upconverter Section
2. Power Amplifier
3. Power Supply System
4. Monitoring and Diagnostic Circuits - connectors and switches.
5. On-Delay Timer Assembly.
In addition, microwave isolators and filters are used as necessary to ensure the stability
and purity of transmitted signals.
2.1 Upconverter Section
The Upconverter Section is comprised of the following major functional circuits or
modules:
1. Hybrid Local Oscillator
2. Upconverter/ Mixer
3. Filter Assembly
Hybrid Local Oscillator – The local oscillator consists of a crystal oscillator, frequency
multiplier, and a band pass filter all encapsulated in solid 6061-T6 aluminum. The output
of the local oscillator provides pump power to the signal upconverter. The local oscillator is
powered by +12 VDC.
Upconverter Mixer – The translation from VHF to microwave frequencies takes place
here. The mixer is also called an "upper sideband upconverter". The desired output of
the upconverter is a signal at a frequency, which is the sum of the local oscillator, and
VHF input frequencies. The upconverter also generates unwanted signals which have to
be filtered out, among them the "lower sideband", LO leakage, and others.
Filter Assembly – There are two filters. The group band-pass filter is tuned to pass the
upper sideband. The notch filter is tuned to attenuate the local oscillator leakage without
affecting the output signal.
2.2 Power Amplifier Chains
The power amplifier is a state of the art linearised device with a 1 dB compression point of
100-Watts average (50 dBm). The design incorporates four stages of amplification in
series, each incorporating pre-matched GaAs (Gallium Arsenide) power modules. The
total gain is approximately 40 dB. In addition to the microwave circuits, the amplifier
includes DC voltage regulator circuits, output RF monitoring circuits, and TTL-actuated
power-off capabilities. The TTL circuit uses a 5VDC voltage regulator to turn the power
amplifier’s voltage regulators on or off. +5VDC to the power amplifier will activate the TTL
circuit, causing the amplifier to turn itself off.