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Gambrills MD

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  • David
    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.
    Message 1 of 5 , Jul 31, 2011
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      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?
    • David
      Do we know where the Annapolis Site was located? It s not on the ATC locator.
      Message 2 of 5 , Jul 31, 2011
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        Do we know where the Annapolis Site was located? It's not on the ATC locator.
      • 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 3 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 4 of 5 , Aug 1 5:47 AM
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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 5 of 5 , Aug 1 11:35 AM
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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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