Ross 4500DR-104-07, User Manual, Page: 144 / 161

144 • GPS Option SRG-4500 User Guide (v7.0)
Antenna Setup
Does the antenna have a good view of the sky?
• The GPS antenna must be mounted in an outdoor location, and be positioned such that it has an uninterrupted
view of the sky, i.e. with as much of the hemisphere of sky above it in plain view.
• The antenna must be positioned away from any buildings or surfaces that could cause reflections to be received
by the antenna.
• If you are mounting the antenna on a wall bracket, this assembly must be placed at the top of the wall, so as to
gain a clear view of the sky above.
• The GPS antenna cannot be mounted indoors; not even against a window, even one without an anti-glare coating.
Check for Radio Frequency Interference
RF Interference into the GPS/GLONASS receiver tends to be the biggest problem when determining why the
system performance is not meeting expectations. The GPS and GLONASS signals are at -130dBm and lower. If
signals higher than this are presented to the receiver it can be overwhelmed. The SRG-4500 can reject CW in-band
jamming signals, but would still be affected by non-CW signals. It is recommended to move the antenna away from
any source of interference or shield the RF interference to prevent it from getting to the antenna.
The most common source of interference is digital noise. This is created by the fast rise and fall times and high
clock speeds of modern digital circuitry. For example, a popular net book computer uses an Atom processor clocked
at 1.6GHz. This is only 25MHz away from the GPS signal and virtually at the same frequency as the GLONASS
signal. Because of the nature of the address and data lines, this would be broadband digital noise at a relatively high
level. Such devices are required to adhere to a regulatory standard for emissions such as FCC Part 15 Subpart J
Class B or CISPR 22 .
It is recommended to move the antenna away from the source of interference or shield the digital interference to
prevent it from getting to the antenna.