100-M0167X2
5 of 21
GMS Inc. doing business as Cobham Tactical Communications and Surveillance
www.cobham.com/tcs
1.
CAUTIONS AND WARNINGS
1.1.
ELECTROMAGNETIC RADIATIONS
There is no consensus in the scientific community about the potential harmful effect of
electromagnetic radiations. This power amplifier will
radiate an average 2 W power with peak powers
14 dB higher (when operating with a COFDM –DVBT transmitter). It is recommended that the operator
minimizes exposure to
electromagnetic radiations by:
A)
Avoid direct proximity to the antenna when the transmitter is turned ON.
B)
Use a low leakage attenuator when the transmitter is operated for testing on a bench.
1.2.
SUPPLY VOLTAGE AND CURRENT
The amplifier is designed for a wide input voltage (9-32 Vdc). Make sure that the power supply has a
voltage within this range and is capable of providing the current needed with some margin. At 12 Vdc
the amplifier will draw less than 1.6 A in High Linearity mode when the input power is properly set to
deliver 2 W. The efficiency of the amplifier remains about constant as the voltage changes. Therefore
the current draw at 24 Vdc will be about half and the current draw at 9 Vdc will be about 30% more.
Make sure your power supply is capable of delivering the current needed. Current limiting should be
avoided as it may induce oscillatory voltage fluctuations that might damage the amplifier.
The Power Amplifier is reversed polarity protected.
1.3.
PA ENABLE (Fast Switching)
The VEPA-2W incorporates a fast switching PA Enable (PIN-5) function. This PIN is LVTTL compatible
(3-5Vdc) and must be tied logic high for the VEPA-2W to operate. The +5VDC output (PIN-4) can be
tied to the PA_ENABLE (PIN-5) if the user does not need to access the PA Enable functionality. The
voltage on this pin should not exceed 5.5VDC.
1.4.
RF LOAD TERMINATION (50 Ohm)ΩΩ
Always terminate properly the RF output port into a well matched antenna. The amplifier has an
internal protection circuit which will cause an internal input switch to open and disconnect the RF input
when there is a RL lower than 5-6 dB (VSWR protection is not available in C2 band VEPA). The switch
will remain in an open latched condition until the poor load condition is corrected and the DC input
power is cycled OFF and ON (the external LED will monitor the protection circuit activation, will remain
green during normal operation and turn red when the PA has entered protection mode, also FAULT 1
(PIN2) will toggle logic high). The protection circuit may not be 100% effective in protecting the
amplifier for infinite mismatch at full Pout at all angles of reflection.
A well matched antenna should always be used. The reflected power will decrease the link range and
will be dissipated internally in the PA, thus increasing the size of the heat-sink needed.