Subject: 1pps Delays in Equipment Room

From: Roger Norrod <[email-masked]>
Date: Wed, 31 Jan 2001 15:26:21 -0500

File:  Electronics   Keys: Electronics, Test

On 1/31/2001, delays of the 1PPS signal at various points in the Equipment
Room were measured.  A Fluke 6681 Timer/Counter was used to measure the
delays.  Two RG223 cables about 25 feet long, and matched to 0.3 nS were
used to connect to the test points.  The Fluke counter A input was
connected to the cable normally connected to the A input of the Racal/Dana
counter in the 1PPS Measurement system located in the Timing Center rack.
The 1PPS Mux was locked to the X0 input, the Site Time 1PPS from the Trak
clock.  The Fluke counter B input was then connected to various points in
the 1pps distribution system in the Equipment Room:

1)  To the cable normally connected to the Racal/Dana B input (mux locked
to X0).  A to B measured 2.8 nS.  With oscilloscope, both pulses had rise
times of about 20 nS.  (The trigger level of both inputs to the Fluke
counter was set to 1.0 Volts, 50 Ohm input impedance for all these
measurements.)

2)  To the input of the 1PPS Buffer in LAN Rack RNG3-8, by connecting to a
BNC Tee at the chassis input.  A to B measured 55.3 nS.

3)  To the "L" output of the 1PPS Buffer in RNG3-8.  A to B measured 78.5
nS.  (Checked five or six of the unused outputs and all were within 1 nS of
this value.)

4)  To the cable normally connected to the 1PPS input of the DCR, WC541.  A
to B measured 94.2 nS.

5)  To the cable normally connected to the 1PPS input of the Spectral
Processor, WC542.  A to B measured 96.3 nS.

6)  To the cable normally connected to the 1PPS input of the GBT
Spectrometer, WC543.  A to B measured 107.4 nS.

7)  To the cable normally connected to the 1PPS input of the LO Reference
Receiver located in the Analog Filter Rack, WC54.  A to B measured 129.2 nS.

Roger Norrod
1/31/2001