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Re: Gambrills MD

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  • widebandit
    TD2 only needed single-phase... Some TD2 sites way out in the boonies - like Cutter New Mexico - were fed by a single wire(!)... TH radio (BSTJ November 1961)
    Message 1 of 5 , Jul 31, 2011
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      TD2 only needed single-phase...

      Some TD2 sites way out in the boonies - like Cutter New Mexico - were fed by a single wire(!)...

      TH radio (BSTJ November 1961) used three-phase power to run synchronous motor-alternators...

      With TH radio, the decision was made to feed the bays with "firm AC" and derive necessary DC potentials locally...

      The solid-state DC-DC converter had yet to be developed...

      So a TH station used from four to seven motor alternators to supply the necessary firm AC to radio bays and FM terminals...

      The 508A motor-alternator set was a fairly sophisticated unit...

      The AC motor and alternator were both brushless...

      Alternator was self-exciting with on-rotor rectifiers...

      At start-up the AC motor ran as a simple squirrel cage induction motor; internal flux pathways were designed into the rotor so that as it came up to speed it would "pull into" synchronous rotation...

      There was also a DC motor on the same shaft...

      When AC power failed the DC motor took the load until station generators fired up and came on-line...

      The DC brushes were lifted by solenoids to eliminate wear until they were needed. When commercial AC failed, the solenoids dropped the brushes onto the commutator; taking DC current from 130V station battery plant...

      Needless to say, TH radio was pretty much a power hog...

      This also explains why, when solid-state TD3 & TH3 came online, radio repeater buildings suddenly went from 3,000 sq ft palaces to 1,200 sq ft bungalows...

      Remember, all this and more may be found at:

      <http://www.alcatel-lucent.com/bstj/>

      - waw -

      >
      > Went by Gambrills today. Don't confuse this with the site within the state
      > park off to the west; this is north of BGE's Waugh Chapel switchyard &
      > south of BWI.
      >
      > I'll have pictures later but for now, it's ATC # 88042, FCC ARS: 1036149.
      >
      > It's down a suburban street, off a 2-lane route.
      >
      > It's been dehorned and has multiple cell carriers and other users.
      >
      > Besides the peeling paint on the tower and building, one thing I noticed is
      > it is fed with single-phase power, and I see no 3-ph primaries on the
      > street going to it that might have fed it with same.
      >
      > I thought all TD-2 sites were fed with 3-phase?
      >
    • OZOB99
      ... A photo of the similar 505D L3 2 motor power plant is in the group s photos:
      Message 2 of 5 , Aug 1, 2011
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        --- In coldwarcomms@yahoogroups.com, "widebandit" <widebandit@...> wrote:
        >
        > TD2 only needed single-phase...

        >
        > So a TH station used from four to seven motor alternators to supply the necessary firm AC to radio bays and FM terminals...
        >
        > The 508A motor-alternator set was a fairly sophisticated unit...
        >
        > The AC motor and alternator were both brushless...
        >
        > Alternator was self-exciting with on-rotor rectifiers...
        >
        > At start-up the AC motor ran as a simple squirrel cage induction motor; internal flux pathways were designed into the rotor so that as it came up to speed it would "pull into" synchronous rotation...
        >
        > There was also a DC motor on the same shaft...
        >
        > When AC power failed the DC motor took the load until station generators fired up and came on-line...
        >
        > The DC brushes were lifted by solenoids to eliminate wear until they were needed. When commercial AC failed, the solenoids dropped the brushes onto the commutator; taking DC current from 130V station battery plant...

        A photo of the similar 505D L3 2 motor power plant is in the group's photos:

        http://groups.yahoo.com/group/coldwarcomms/photos/album/2132300760/pic/1090751865/view?picmode=

        Later TH stations had the much smaller & efficient 508H(?) solid state converters.I don't recall whether they required 3 phase inputs or not.
      • David
        ... Wow; SWER is not common in the US. Did everything in TD2 run off of battery plant directly? ...
        Message 3 of 5 , Aug 1, 2011
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          On 8/1/11 1:31 AM, widebandit wrote:


          > Some TD2 sites way out in the boonies - like Cutter New Mexico - were fed by a single wire(!)...

          Wow; SWER <https://secure.wikimedia.org/wikipedia/en/wiki/SWER> is not
          common in the US.

          Did everything in TD2 run off of battery plant directly?


          > TH radio (BSTJ November 1961) used three-phase power to run synchronous motor-alternators...

          <http://www.alcatel-lucent.com/bstj/vol40-1961/articles/bstj40-6-1627.pdf>
          is an interesting read.

          I have no idea how the synchronous motor with no excitation works. It's
          common to start a synchronous motor via induction, then apply excitation.

          The self-excited generator is now pretty common.

          The dual motor scheme is an old idea; I recall a pipeline firepump with AC
          and diesel powerplants straddling the pump.

          > With TH radio, the decision was made to feed the bays with "firm AC" and derive necessary DC potentials locally...

          Note the 508A had a fair-sized flywheel; clearly that was an important
          aspect of the design. A large flywheel was a good filter, and bridged the
          spikes of going from one power source to the other.

          Note many ISP's are using a similar scheme; HiTek units are used at some
          carrier hotels [hosting sites...]. They last long enough for the Diesel to
          start & get to speed.

          I see mention of L-carrier in the above; so coax undergrounds used 508A's
          as well?
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