User's Manual

Radio Activity S.r.l. 18 / 44
Power amplifier works in C class and ensures a very high efficiency, lowering the needed power from supply
system and lowering the thermal dissipation inside the cabinet. When used at full power and high duty cycle
rate, the temperature of the equipment can increase some tens of °C over the ambient temperature. Inside
KAIROS a thermal sensor is hosted and it is directly connected to the internal microcontroller which enables
the command for air forced cooling fan of the cabinet if the temperature rises over 85°C. For heavy duty
applications it is recommended to assure appropriate ventilation and to protect users to accidentally touch
the equipment when hot.
The current flowing into final amplifier transistor is continuously monitored by microcontroller to verify the
correct functioning and to reveal an eventual efficiency degradation.
KAIROS is equipped with an harmonic filter to lower spurious emissions under required levels by existing
regulations.
In some applications, for example in multi carriers assembly or in sites with many transmitters, it is
recommended to use isolators/circulators to reduce possible intermodulation problems. Note that an
isolator assures only a limited isolation bandwidth: it can’t isolate a VHF TX from a UHF one! In similar cases
diplexers or cavity filters should be used.
Unless the TX has got a built-in protection to a load mismatching, it is strongly recommended to achieve at
the TX output connector a VSWR (referenced to 50 Ohm) between 1 to 1.3.
3.3.3 GPS antenna
KAIROS may be (optionally) equipped with an embedded receiver for GPS service, with high precision Pulse
Per Second (PPS) output function in order to synchronize the station. Only an external active antenna is
required.
The specifications of the external GPS antenna are:
Connector (RF + remote power supply)
SMA
Impedance
50 Ohm
Sensitivity Tracking
up to
-
159 dBm
Antenna gain
From 20 to 45 dB, depending on cable length, to obtain a total gain
between 12 dB and 26 dB (assumes a 3 dBic patch antenna).
A typical value of 25 dB is best in most cases.
Frequency band
GPS L1 1575.42 +/
-
10 MHz
Maximum Noise Figure
< 2.5 dB including
pre
-
selector
DC Voltage
5Vcc @ max 100mA superimposed into the SMA RF connector
Out of Band Rejection
-
60 dB @ +/
-
50 MHz off center frequency
Lightening Protection
90 V, 20 kA, 8/20
-
S
Suggested model
GPS
-
TMG
-
SP
-
40N from PCTEL Broadband Technology
The GPS quality and the effective antenna efficiency can be checked connecting to the equipment through
the setup tool: