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Hardened microwave dish, AT&T Monrovia, MD

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  • Albert LaFrance
    Today I learned more about the hardened microwave dish at Monrovia, which talked to the Leesburg 5 troposcatter station. The dish was installed in 1969. The
    Message 1 of 6 , Jul 19 9:14 PM
      Today I learned more about the hardened microwave dish at Monrovia, which
      "talked" to the Leesburg 5 troposcatter station.

      The dish was installed in 1969. The AT&T technician showed me a set of
      photos, some dated Nov. 1969, detailing the construction of the concrete
      foundation and installation of the dish. To put that date into context,
      we've learned from a posting on this list that the tropo stations opened
      around 1965, and from Loudoun Country records that some construction
      activity apparently was under way at Leesburg 5 in April 1968.

      The concrete foundation on which the dish rests is not a solid block, but
      rather the top of a heavily-reinforced hollow shaft extending down to an
      elevation about eight feet above the lower-level floor of the two-story
      underground building. The shaft is outside the building's footprint; to
      enter the shaft from the lower-level floor, you climb up a short ladder to a
      small balcony, go through a conventional metal door in the exterior wall,
      and a walk through a short (I'd guess about 15-20 ft.) concrete tunnel. The
      tunnel connects to the bottom of the shaft, where a caged ladder goes up
      about 25-30 ft. to the top of the shaft. Also running up the shaft is a
      single 4 GHz waveguide for the dish, and electrical conduits for lights and
      for the radiation detector on the dish's feed arm.

      The foundation is designed to accommodate two dishes, but only one was ever
      installed. The opening for the second dish is covered by a heavy circular
      steel plate, bolted down.

      The dish is a concrete-filled steel shell, with lifting lugs welded to both
      sides, secured at the bottom by bolts. The photos show that the dish was
      factory-built, with the feed arm shipped as separate component.

      The feed aperture appears as a circular flange, with bolts around the
      perimeter and a rectangular window in the middle. At one time, a report of
      noise on the microwave link was traced to a hornet's nest built at the feed
      point!

      The hardened dish is no longer in service; the radio link to Leesburg 5 is
      now provided by a conventional high-performance parabolic antenna mounted
      low on the microwave tower. The Western Electric TD-2 radios have been
      replaced by Northern Telecom RD-4A equipment, also operating in the 4 GHz
      band, with two working channels and one protection channel.

      Albert
    • David Lesher
      ... This means there s a lightweight door in the shell of the building? It strikes me as rather pointless to have big, heavy blastproof doors...only some of
      Message 2 of 6 , Jul 20 11:06 AM
        Unnamed Administration sources reported that Albert LaFrance said:
        >
        > The concrete foundation on which the dish rests is not a solid block, but
        > rather the top of a heavily-reinforced hollow shaft extending down to an
        > elevation about eight feet above the lower-level floor of the two-story
        > underground building. The shaft is outside the building's footprint; to
        > enter the shaft from the lower-level floor, you climb up a short ladder to a
        > small balcony, go through a conventional metal door in the exterior wall,
        > and a walk through a short (I'd guess about 15-20 ft.) concrete tunnel. The
        > tunnel connects to the bottom of the shaft, where a caged ladder goes up
        > about 25-30 ft. to the top of the shaft. Also running up the shaft is a
        > single 4 GHz waveguide for the dish, and electrical conduits for lights and
        > for the radiation detector on the dish's feed arm.

        This means there's a lightweight door in the "shell" of
        the building? It strikes me as rather pointless to have
        big, heavy blastproof doors...only some of the time.



        --
        A host is a host from coast to coast.................wb8foz@...
        & no one will talk to a host that's close........[v].(301) 56-LINUX
        Unless the host (that isn't close).........................pob 1433
        is busy, hung or dead....................................20915-1433
      • Albert LaFrance
        Looking over my previous posting, I realize my explanation wasn t clear on that subject. The tunnel and shaft are themselves hardened, so that they re really
        Message 3 of 6 , Jul 20 12:41 PM
          Looking over my previous posting, I realize my explanation wasn't clear on
          that subject. The tunnel and shaft are themselves hardened, so that they're
          really extensions of the blast-protected building envelope. The exposed top
          of the shaft (including the dish and the steel plate over the adjacent
          unused opening) is the actual barrier between the exterior and interior
          atmospheres. In other words, the "tunnel side" of the door is inside the
          building, in terms of being a protected environment, although it's outside
          the building's original floor plan.

          There were, however, some dead insects and spiders in the tunnel. I don't
          know if these came from the top of the shaft through a small gap in the dish
          attachment, or if they arrived after the building ceased to be fully
          hardened during the renovation completed a few years ago, and migrated to
          the tunnel because it's dark and undisturbed.

          Albert

          ----- Original Message -----
          From: "David Lesher" <wb8foz@...>
          To: <coldwarcomms@yahoogroups.com>
          Sent: Saturday, July 20, 2002 2:06 PM
          Subject: Re: [coldwarcomms] Hardened microwave dish, AT&T Monrovia, MD


          > This means there's a lightweight door in the "shell" of
          > the building? It strikes me as rather pointless to have
          > big, heavy blastproof doors...only some of the time.
        • David Lesher
          ... Even so, I can t see how it would have helped the structural integrity of the facility. But this raises a question. What level of give did the various
          Message 4 of 6 , Jul 20 12:50 PM
            Unnamed Administration sources reported that Albert LaFrance said:
            >
            > Looking over my previous posting, I realize my explanation wasn't clear on
            > that subject. The tunnel and shaft are themselves hardened, so that they're
            > really extensions of the blast-protected building envelope. The exposed top
            > of the shaft (including the dish and the steel plate over the adjacent
            > unused opening) is the actual barrier between the exterior and interior
            > atmospheres. In other words, the "tunnel side" of the door is inside the
            > building, in terms of being a protected environment, although it's outside
            > the building's original floor plan.

            Even so, I can't see how it would have helped the structural integrity
            of the facility.

            But this raises a question. What level of "give" did the various
            utility egresses have in the undergrounds? And how? It's pointless
            to have a $500K (1971 $) station that survives if the cables get
            crimped at the wall when there's a hit 10 miles away, etc...

            > There were, however, some dead insects and spiders in the tunnel. I don't
            > know if these came from the top of the shaft through a small gap in the dish
            > attachment, or if they arrived after the building ceased to be fully
            > hardened during the renovation completed a few years ago, and migrated to
            > the tunnel because it's dark and undisturbed.

            I can not imagine a structure outside of a true pressure vessel
            (submarine, etc) that does not have some infiltration from insects.
            And where there are insects, there are spiders to eat same.



            --
            A host is a host from coast to coast.................wb8foz@...
            & no one will talk to a host that's close........[v].(301) 56-LINUX
            Unless the host (that isn't close).........................pob 1433
            is busy, hung or dead....................................20915-1433
          • Albert LaFrance
            ... From: David Lesher To: Sent: Saturday, July 20, 2002 3:50 PM Subject: Re: [coldwarcomms] Hardened
            Message 5 of 6 , Jul 24 6:32 PM
              ----- Original Message -----
              From: "David Lesher" <wb8foz@...>
              To: <coldwarcomms@yahoogroups.com>
              Sent: Saturday, July 20, 2002 3:50 PM
              Subject: Re: [coldwarcomms] Hardened microwave dish, AT&T Monrovia, MD


              > But this raises a question. What level of "give" did the various
              > utility egresses have in the undergrounds? And how? It's pointless
              > to have a $500K (1971 $) station that survives if the cables get
              > crimped at the wall when there's a hit 10 miles away, etc...

              Good question. My view is that with the building and the cable firmly and
              completely embedded in the same solid medium - the earth - and subject to
              the same forces, there shouldn't be much relative movement between the two
              as a result of seismic shock from a nuclear blast.

              The situation would be different for an above-ground building, because its
              inertia and height might cause it to slide or rock in response to the shock
              wave. In that regard, it would be interesting to find out what measures are
              taken to protect cables and pipes entering buildings in high-risk earthquake
              zones. In addition, the building would be subject to the atmospheric blast
              pressure.

              A condition which might endanger cables entering an underground facility
              would be if there was an unstable geologic fault near or under the building,
              so that the entire volume of earth containing the building and cables might
              not move as a single body. I assume engineering studies would investigate
              that risk in selecting a site for an underground facility.

              Albert
            • Albert LaFrance
              Looking over the site plan for the underground station at Finland, PA (Finland No. 2), I saw something possibly relevant to the issue you brought up. The plan
              Message 6 of 6 , Jul 29 12:03 PM
                Looking over the site plan for the underground station at Finland, PA
                (Finland No. 2), I saw something possibly relevant to the issue you brought
                up.

                The plan shows what appear to be underground conduits for each of the
                two coaxial cables entering the building, plus another conduit (which
                could be for power or communications) between the underground building and
                the adjacent above-ground microwave station.

                I've posted a portion of the plan at:

                http://longlines.addr.com/places-routes/Finland/plot_plan.html

                The red line coming out of the conduit from the NW (upper left) corner of
                the building is labeled: Finland "2" - Laurelton "A" Cable. The red line
                from NE conduit is labeled: Cherryville - Finland #2 "A" Cable.

                The coax conduits are roughly 80 and 120 feet in length, and their distant
                ends terminate at rectangular structures labeled "cable headwalls".

                It's interesting that the conduits are curved, with their radii noted. I
                wonder if this was merely to ensure that the conduits enter the building
                walls perpendicular to the wall, or if the curves were intended to give the
                conduits some "springiness".

                The conduits themselves could been provided merely to avoid the necessity
                for cable-installation crews to dig trenches in the immediate vicinity of
                the underground building, with the attendant risk of damaging pavement,
                landscaping, or the building wall. Or they could have been part of the
                blast-protection design (or both).

                Albert

                ----- Original Message -----
                From: "David Lesher" <wb8foz@...>
                To: <coldwarcomms@yahoogroups.com>
                Sent: Saturday, July 20, 2002 3:50 PM
                Subject: Re: [coldwarcomms] Hardened microwave dish, AT&T Monrovia, MD

                <SNIP>
                > But this raises a question. What level of "give" did the various
                > utility egresses have in the undergrounds? And how? It's pointless
                > to have a $500K (1971 $) station that survives if the cables get
                > crimped at the wall when there's a hit 10 miles away, etc...
                <SNIP>
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