A member of the Olancha Group Ltd
Registered in England No. 08405712
VAT Registration No. GB163 04 0349
Siretta Ltd
Basingstoke Road
Spencers Wood
Reading
Berkshire RG7 1PW
sales
fax
email
web
+44(0)118 976 9014
+44(0)118 976 9020
www.siretta.co.uk
33
ZETA Series
GPRS/UMTS/LTE Terminal with GPIO
GPS Antenna Gain
Antenna gain is defined as the extra signal power from the antenna as compared to a
theoretical isotropic antenna (equally sensitive in all directions).
It is important to note that GPS antenna gain is not the same thing as external LNA
gain. Most antenna vendors will specify these numbers separately, but some combine
them into a single number. It is important to know both numbers when designing and
evaluating the front end of a GPS receiver.
An antenna with higher gain will generally outperform an antenna with lower gain.
Once the signals are above about -130 dBm for a particular satellite, no improvement
in performance would be gained. However, for those satellites that are below
about -125 dBm, a higher gain antenna would improve the gain and improve the
performance of the GPS receiver. In the case of really weak signals, a good antenna
could mean the difference between being able to use a particular satellite signal or
not.
As the GPS antenna needs to be located away from the ZETA series Modem then
an active antenna will be required to obtain the best system performance. The active
antenna has its own built in low noise amplifier to overcome RF trace or cable losses
after the active antenna. The active antenna has a low noise amplifier (LNA) with
associated gain and noise figure.
GPS Antenna Connector (Optional)
GPS Antenna Polarization
The GPS signal as broadcast is a right hand circularly polarized signal. The best
antenna to receive the GPS signal is a right hand circularly (RHCP) polarized antenna.
GPS Antenna
The GPS antenna we recommend to use for the ZETA series is the Mike 3A SMA
male magnetic mount antenna. Please turn to
page 44
for ordering details on
the Mike 3A, alternatively visit
www.siretta.co.uk/mike3a-p-302.html
for more
information about this antenna.
Figure 25.
Mike 3A GPS antenna
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