AT&T microwave course - Unit 1 - amended
- Here are the notes again, with one item I forgot added at the end.
TD2 and TD3 radio operate in 3700-4200 MHz band.
TD2 has 600 voice circuits per radio channel, TD2A has 900, TD2B and TD3
TD2 uses vacuum tubes, except the Receiving Modulator and IF Preamp in the
TD2B are solid state.
TD3 is solid state, except the Transmitting Amplifier is a traveling wave
A fully-equipped TD2 or TD3 system has 6 regular channels and 6
interstitial channels (slot frequencies). All 12 channels are combined on
one transmit and one receive antenna.
Repeaters are referred to as "auxiliary stations". At these stations, the
received signal is amplified and shifted by 40 MHz before re-transmission
to avoid overshoot and feedback between the transmit and receive antennas,
called "repeater singing".
Antenna orientation is quite critical due to 2-degree beamwidth of the horn
Signal polarization is used to minimize interaction between the regular and
Two types of waveguide construction were used: inside and outside. Outside
waveguide is of slightly heavier construction and has airtight flange
At the building weatherseal (waveguide hatch), there's a fitting called a
"waveguide pressure window". It's section of rectangular waveguide with a
sheet of mica across the entire area of the waveguide opening. It allows
pressurization of the outside waveguide and antenna to keep moisture out.