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28 Trimble ThunderBolt E GPS Disciplined Clock User Guide
In cases where the distance between the Bullet and the ThunderBolt E is excessive (for
example when the loss exceeds 18 dB), an inline amplifier is necessary.
The following table shows the loss relationships:
In cases where the run length is such that the loss exceeds 18 dB, an inline amplifier
(LNA) with the following specifications is required:
• Place the LNA at a point in the coaxial line so that the loss between the Bullet
antenna and the LNA does not exceed 18 dB.
• The noise figure of the LNA must be 3 dB or less. The gain of the LNA should be
at least 3 dB greater than the cable loss between the output of the inline LNA
and the ThunderBolt E input. Trimble recommends that a filtered LNA is used
to reduce overload by out-of-and signals. (Filtered LNAs are made by GPS
Networking.)
For example, if you choose an RG-6 cable with 40 dB/100 meter loss, and the
required run-length is 90 meters, the total loss for his run would be
(0.9)(40 dB/100 meters) = 36 dB. This exceeds 18 dB and means that you need to
use an inline amplifier.
However, if you select an LMR-400 or LMR-600 cable, you would not need an
inline amplifier.
• The noise figure of the inline amplifier must be 3 dB or less. The gain of this LNA
would be 21 dB (18 dB loss precedes LNA, 18 dB of loss follows LNA, and drives
requirement for 18 + 3 = 21 dB gain for the LNA).
Cable type dB / 100 ft dB / 100 meter Max lenght for 18 dB loss at
1575 MHz (feet / meter)
RG-6 12 40 150/45
RG8 (and 8/U) 9.6 31 185/58
RG-8X 16.8 55 107/33
RG-58 19.6 64 92/28
RG-59 14.7 48.2 122/37
LMR-400 5.3 17.2 340/105
LMR-600 3.4 11.2 530/161
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