Hamilton Jet HTX30, Product Manual

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HTX30 Product Manual Component Installation
4-9
Avoiding VHF interference
VHF interference from cellular phones and radio transmitters may affect GPS signal quality and degrade
JETanchor performance. To maximise GPS reception and JETanchor performance, the GPS antenna should
not be installed within an exclusion zone around any VHF radio mast. The exclusion zone forms a truncated
cone with a radius of 1.5 m (5 ft) at the masthead and 1 m (3 ft) at the mast's base, as shown in the following
figure.
1 - 1.5 metre minimum radius at radio masthead.
2 - Radio mast.
3 - Exclusion zone where GPS antenna should not be
mounted.
4 - 1 metre minimum radius at base of radio mast.
Figure 10: Exclusion zone for GPS antenna installation
When evaluating the possibility of radio interference, consider the following:

VHF radios emit strong harmonics. The 10th harmonic of VHF radio, in some channels, falls within the
GPS working frequency band, which may cause the SNR of GPS to degrade significantly.

VHF marine radio working frequencies (channels 1 to 28 and 84 to 88) range from 156.05 to 157.40 MHz.
The L1 GPS working centre frequency is 1575.42 MHz. The bandwidth is +/- 2MHz to +/- 10 MHz, which is
dependent on the GPS antenna and receiver design.

The strength of radiated harmonic signals vary greatly between different brands and models of radio
equipment.

Hand-held 5W VHF radios may not provide suitable filtering and may cause significant interference issues
if operated in close proximity to the GPS antenna.

In all cases follow the VHF radio manufacturers’ recommendations for minimum clearance distances to
other equipment, which may be greater than the minimum distances specified in this section.
GPS antenna weight (excluding mounting
adaptor): 0.75 kg.
Figure 11: GPS antenna dimensions
(without mounting adapter)
Mounting the GPS antenna
The GPS antenna can be mounted on a pole or on a flat surface. A pole mounting adaptor kit can be ordered
from HamiltonJet ( ► page 2-6).
For detailed mounting instructions, see the Hemisphere user guide that ships with the antenna.