Subject: [IGEXMail-0765] NPLB and NPLC interruption
From: Jon Clarke <[email-masked]>
Date: 19 May 2000 12:30:47

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IGEXMail                19-May-2000 12:30:47                   Message No 0765
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Author: Jon Clarke <[email-masked]> 
Subject: NPLB and NPLC interruption 

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Dear Colleagues,=20

during a lightning storm yesterday (about 16:00 UT, 18 May 2000) the =
1pps reference for our Ashtech NPLB and R100 NPLC jumped (to our =
frustration...).=20

It's not clear to us why this should have happened, as all our 1pps and =
5MHz distribution equipment is now on uninterruptible power supplies, =
ruling out a power interruption. There were no lightning strikes nearer =
than several kilometres away, ruling out direct interference. There is a =
200m cable taking a 5MHz between our two buildings, and it lies next to =
other cables. There may have been interference due to this, perhaps a =
large transient on a nearby cable due to a strike on electrical =
equipment elsewhere. To reduce any effects, we have now put an RF =
transformer on the 5MHz supply cable to avoid any ground current flow =
into our distribution equipment.=20

Today (11:00 UT, 19 May 2000) we have reset the reference and equipment. =

Regards,=20
Jon=20

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Mr Jon Clarke                                Time and Frequency Section,
[email-masked]      Centre for Electromagnetic and Time Metrology,
tel: +44 (0) 20 8943 6548                  National Physical Laboratory,
fax: +44 (0) 20 8943 6529        Queens Road, Teddington, TW11 0LW, U.K.
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