provide power to the antenna. Changing the antenna model will impact the system calibration,
so users should take that into consideration if they choose to switch to a different antenna.
Q7: What type of GNSS antenna cable should I use?
A7: The antenna cable should have less than 10 dB of loss at 1.5 GHz. If this is not possible due
to the cable type or length of cable, then additional in-line amplifiers will be need to be
installed or you will need a cable type with less loss. Microsemi recommends use of “LMR-240”
or “LMR-400” type antenna cables, which are available for purchase from multiple vendors.
Prefabricated antenna cables of both types in standard lengths, e.g., 20 m, 30 m, 40 m, 45 m
and 60 m (LMR-400 only), can be purchased directly from Microsemi. These cables include
TNC(M) connectors at both ends. The unit requires a minimum of 15 dB of gain from the
antenna combined with the loss in the antenna cable. The antenna included with the 4380A
has 25 dB of gain, so as noted earlier, the total cable losses in the system must not exceed 10
dB at 1.5 GHz. Please ensure the antenna gain combined with the cable loss will provide
sufficient signal strength for the 4380A if you are using a different antenna.
Q8: How do I determine my GNSS antenna cable delay?
A8: Accurately measuring the signal delay for a GNSS antenna cable can be challenging without
the right equipment. One method is to use a high quality oscilloscope in conjunction with the
4380A to measure the transit time of a pulse over the length of the cable. That method
requires that the 4380A is configured with a pulse output module (4394A) and a 10 MHz output
module (4395B-10). A second method is to use a 4380A that is configured with a pulse input
measurement module (4393A) that serves as a Time Interval Counter (TIC), along with a pulse
output module (4394A). Alternatively, for a nominal additional charge, the antenna cable delay
can be precisely measured at the Microsemi factory. The delay is then printed on a plastic
coated label that is affixed to the cable. For the highest performance applications, a full system
calibration can be performed at the Microsemi factory that accounts for time delays in the
GNSS antenna, antenna cable, and GNSS receiver.
Q9: How do I know when I need to use a GNSS signal amplifier with my antenna cable?
A9: If the location of the antenna dictates that a longer cable must be used, then a line
amplifier will need to be inserted into the signal path or you will need to run an antenna cable
with less loss. A line amplifier is a device used to amplify the GNSS signal to overcome the
losses resulting from longer cable runs. In selecting a line amplifier, it is necessary to make sure
that it provides an adequate amount of gain and that it operates from 1200 MHz to 1600 MHz.
The amount of gain required from a line amplifier can be calculated by knowing the total loss of
the antenna cables being used. The signal loss due to a cable varies depending upon the quality
of the cable and the frequency of the signal. For the purposes of GNSS antennas, the cable loss
should be calculated at 1500 MHz. The manufacturer of the cable being used should be able to
provide an estimate of the cable loss at 1500 MHz. Once the cable loss is known, it can be
inserted into the equation below to calculate the required gain of the line amplifier.
© 2016 Microsemi Corporation. All rights reserved. SyncSystem 4380A FAQs Version 1.0 (22 Feb 2016)
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