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AT&T microwave course - Unit 1 - amended

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  • Albert LaFrance
    Here are the notes again, with one item I forgot added at the end. Albert ... TD2 and TD3 radio operate in 3700-4200 MHz band. TD2 has 600 voice circuits per
    Message 1 of 1 , Jan 21, 2001
      Here are the notes again, with one item I forgot added at the end.

      Albert

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      TD2 and TD3 radio operate in 3700-4200 MHz band.

      TD2 has 600 voice circuits per radio channel, TD2A has 900, TD2B and TD3
      have 1200.

      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
      tube.

      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
      reflectors.

      Signal polarization is used to minimize interaction between the regular and
      interstitial frequencies.

      Two types of waveguide construction were used: inside and outside. Outside
      waveguide is of slightly heavier construction and has airtight flange
      connections.

      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.

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