V1.1 – Mar-11
User’s Manual
Page 10 of 18
Further information is given in
•
Chapter “6.2 DIP Switch Settings” and
•
Maestro’s GPS Receiver A1084 Product Manual
4.2.1 Passive Antenna
A passive antenna must be connected to the Primary Antenna connector (passive
antenna input). It should be placed as close as possible to the EVA1084-A board
(short cable length). The signal power lost by the antenna cable can not be recovered
by the LNA (Low Noise Amplifier) integrated on the A1084-A GPS receiver.
4.2.2
Active Antenna
4.2.2.1 On Auxiliary Antenna Connector (Active Antenna Input)
General GPS active antenna specification:
Limitations:
•
Supply voltage (voltage fed into VANT pin) 5 V max.
•
Supply current 50 mA max.
Recommendations:
•
Gain
≥
20 dB (should not exceed 26 dB + cable loss)
•
Noise
figure
≤
1.5 dB
The recommendations apply to the majority of active antennas that can be found in
the market. Anyhow, the quality of the GPS antenna chosen is of paramount im-
portance to the overall sensitivity of the GPS system.
4.2.2.2 On Primary Antenna Connector (Passive Antenna Input)
An active antenna connected to the Primary Antenna connector must not exceed a
gain of 10 dB + antenna cable loss according to SiRF recommendation. Exceeding
this gain recommendation should be tested case by case.
The schematics in chapter “10 Board Schematics” show how an antenna supply
voltage can be fed to an active antenna connected to the ANT_INT pin of the
A1084-A GPS receiver and how the antenna supply voltage can be switched on and
off by the RFPWUP signal.
4.2.3 Hints
Unused antenna inputs should be terminated with 50
Ω
±
20%. Do not feed antenna
supply voltage into terminated antenna inputs.