[IGSMAIL-1965] changes planned at USNO

[Jim]

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IGS Electronic Mail      Mon Jul 27 12:43:17 PDT 1998      Message Number 1965
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Author: Jim Ray
Subject: changes planned at USNO

In order to make the following configuration changes, data from the USNO
receiver will be interrupted on Wednesday, 12 August:

   * The AOA TurboRogue SNR12 receiver will be moved to an environmentally
     controlled chamber within the USNO clock vault.  (The receiver will
     not otherwise be changed).  Within the chamber, the temperature is
     controlled to +/- 0.15 C and relative humidity to +/- 1%.

   * A new antenna cable will be installed:

     Antenna cable 24-APR-1997 to 12-AUG-1998:
        Belden RG-214/U -- 200 feet (60.96 m) length (mostly exposed to full
          sun running along rooftop of Bldg 52)
        specifications:
          Velocity factor 0.66
          Capacitance 30.8 pf/foot
          Loss at 1200 MHz 9.0 db/100 foot
          Loss at 1500 MHz 10.1 db/100 foot
          Electrical Length Change versus Temperature:
          3000 PPM over (-10 to 42 C range) or 58 PPM/C
          => 0.2 ps/m/C or 12 ps/C for 200 feet

     Antenna cable 12-AUG-1998 to present:
        Andrew FSJ1-50A (35422-33 phase stabilized) 1/4 inch Superflexible
          Foam Dielectric Heliax -- electrical length will be measured at
          the time of installation (mostly run in the ceiling of the 3rd
	  floor of Bldg 52)
        specifications:
          Velocity factor 0.84
          DC resistance 2 to 3 ohms per 1000 foot
          Capacitance 24.2 pF/foot
          Inductance .061 uH/foot
          Loss at 1250 MHz   6.77 db/100 foot
          Loss at 1500 MHz   7.47 db/100 foot
          Electrical Length Change versus Temperature:
          400 PPM over (-40 to 30 C range) or 5.7 PPM/C
          => 0.02 ps/m/C or 1.2 ps/C for 200 feet

   * A new PC controller will be installed.

An updated station log will be sent to the IGS Central Bureau.

We apologize for the service disruption but are hopeful that the changes will
improve the USNO clock stability and performance by greatly reducing the
sensitivity to temperature changes.

=========================================================================
Jim Ray                                   e-mail: jimr at maia.usno.navy.mil
U.S. Naval Observatory, EO Dept.          phone : 202-762-1444
3450 Massachusetts Avenue, NW             fax   : 202-762-1563
Washington, DC  20392-5420
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[Mailed From: Jim Ray (USNO 202-762-1444) <jimr at maia.usno.navy.mil>]