54
The Setup Menus
7.8
Set Cable Delay
GPS time is referenced to the time it is received by the antenna. Without setting the cable delay,
the time would be late by the time it would take to travel the distance from the antenna to the
GPS receiver. To accurately set the cable delay, you need to know the length and velocity factor of
the antenna cable. For the cable supplied with the Model 1094B, calculate the delay by multiplying
the the length of the cable (in feet) by 1.19 nanoseconds per foot. The result of this calculation
will be in nanoseconds, and you can enter in the whole part of this number into the 1094B. See
Figure 7.9.
Calculating Cable Delay
Use Formula 7.1 below for calculating cable delay for Arbiter-supplied RG-6 antenna cables.
(7.1)
T
=
λ
1
CKv
+ 1
ns
Where:
T = Cable delay, in nanoseconds;
λ
= Cable length, in meters;
C = Speed of light (3
×
10
8
meters per second);
Kv = Nominal velocity of propagation (0.85).
One nanosecond is added to the calculated value to account for the length and velocity factor
of the short connecting cable inside of the clock.
EXAMPLE: A 50-foot antenna cable would contribute the following delay; 50 ft. x 1.19 ns/ft =
59.5 (round up and enter 60).
Figure 7.9: Cable Delay Setup
Numeric Data Entry Mode
Numeric data entry mode is activated anytime you enter a menu
that requires a change in numerical value. Press SETUP to move the cursor to the left; press
ENTER to move the cursor to the right. Press the UP and DOWN keys to adjust values.