EndRun Sonoma N12, User Manual

Page: 147 / 174

S o n o m a U s e r M a n u a l 130
A P P E N D I X E
131 S o n o m a U s e r M a n u a l
I N S T A L L I N G T H E G P S A N T E N N A
Long Cable Runs
Most GPS Time Servers are installed with only 50 feet (15 meters) of antenna cable. However, there
are many circumstances where 50 feet is inadequate. EndRun can accommodate a cable length of up
to 1000 feet using a combination of low-loss cable and preamplifiers.
Recommended Cable
The factory-supplied GPS cable is an RG-59 type. RG-59 is a broad classification, with wide
variation in performance between cables from different manufacturers and for different applica-
tions. EndRun supplies two specific cables: Belden 9104 or Belden 1505A. Both cables are double
shielded, low loss cables designed for the cable TV industry, and have equivalent performance at
the GPS frequency with loss of 10 dB/100 feet. The difference between these two cables is the DC
resistance, which becomes important for very long cables. Belden 9104 is constructed with a copper-
plated steel center conductor and an aluminum outer braid. Belden 1505A is constructed of all solid
copper conductors and has very low DC resistance. For very long cables, if the DC resistance is too
high, not enough voltage will be available at the end farthest from the Sonoma timeserver where the
antenna and preamplifiers are installed. For cable lengths less than 700 feet, Belden 9104 is accept-
able. Longer runs require Belden 1505A.
If you are responsible for the GPS installation and you are supplying the cable, then you must make
sure the cable you install is comparable to these cables, with 10 dB or less of loss per 100 feet at 1.5
GHz. If the cable length is longer than 700 feet, you must make sure that the cable has equivalently
low DC resistance to the Belden 1505A type. Choosing an inferior cable type can cause a myriad of
GPS reception problems. You will also need preamplifiers if the cable length is greater than 250 feet.
See the chart below for details.
Using GPS Preamplifiers
EndRun produces a GPS Preamplifier which is a very high-performance, low-noise, low-power drain,
inline amplifier for difficult GPS signal environments and long cable runs (greater than 250 feet of
factory-supplied cable). The following table shows the number of preamplifers we recommend for
each GPS antenna installation using our factory-supplied cable. Installations using other cable types
may have different preamplifer requirements.
Cable Length Cable
Type
Number of
Preamplifiers
Up to 250 feet
(76 meters)
RG-59
Belden 9104
0
251 to 500 feet
(77 to 152 meters)
RG-59
Belden 9104
1
501 to 700 feet
(153 to 213 meters)
RG-59
Belden 9104
2
701 to 750 feet
(214 to 228 meters)
RG-59
Belden 1505A
2
751 to 1000 feet
(229 to 305 meters)
RG-59
Belden 1505A
3