[IGSMAIL-3412]: NPL time transfer disruption (NPLD, NPLF, AA276, TFS101, TFS102, BIPM F)

[Jon Clarke]

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IGS Electronic Mail      11 Jul 03:44:55 PDT 2001      Message Number 3412
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Author: Jon Clarke, NPL
Subject: NPL time transfer disruption

Dear Colleagues, 

There has been about 72 hours of disruption to NPL's GPS and GLONASS
time transfer receivers but they are now functioning again. My apologies
for this significant interruption in our data. We are changing our
configurations so that we have better protection in the future. 

Regards, 
Jon 

Contents: 
Problems
K-band two-way
X-band two-way
NPLD, Ashtech Z12T
NPLF, Javad Legacy
AA276, AOA TTR5A
TFS101 and TFS102, Motorola Oncores
BIPM F, 3S Navigation R100

Problems
There was a power cut during 7 and 8 July which was not handled properly
for Building 2, which holds most of our time transfer equipment. In
Building 5 a distribution amplifier failed and signals were moved to a
new one, giving a step in the signal chain that forms UTC(NPL) for the
equipment in Building 5, although Building 2 was unaffected. We are
correcting our time interval measurements and time transfer equipment
(where necessary) so that no change is visible to the outside world. 

K-band two-way
Was entirely unaffected by the disruption. The measurements immediately
before and after the weekend were complete and correct. 

X-band two-way
Did not gather data over the weekend, but was otherwise unaffected. 

NPLD, Ashtech Z12T
Has been using a different antenna whilst it was in a common-antenna
configuration with the BIPM's calibrated Ashtech Z12T, BIPMC. As a
result I have not transmitted its data since 1 July. It gathered no data
over the weekend. It was restored yesterday (11 July) and its data is
being transmitted again. 

NPLF, Javad Legacy
As I cannot yet register this GPS/GLONASS receiver with the IGS, I have
stopped tranmsitting its data whilst I use it to characterise some new
monuments. It gathered no data over the weekend. 

AA276, AOA TTR5A
Our reference single-channel GPS CV receiver is sourced differently to
all the other receivers so it was affected by the step in the timescale.
I will start publishing its data again today or tomorrow. 

TFS101 and TFS102, Motorola Oncores
These multi-channel CV receivers gathered no data for the weekend. They
have been restored and their data is being transmitted again. 

BIPM F, 3S Navigation R100
This gathered no data for the weekend. It has been restored and its data
is being transmitted again. 

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Mr Jon Clarke                                 Time and Frequency
Section,
tel: +44 (0) 20 8943 6548  Centre for Electromagnetic and Time
Metrology,
fax: +44 (0) 20 8943 6529                   National Physical
Laboratory,
e-mail: jon.clarke at npl.co.uk                     Queens Road,
Teddington,
web: http://www.npl.co.uk/npl/ctm/                         TW11 0LW,
U.K.
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