100-M0167X2
6 of 21
GMS Inc. doing business as Cobham Tactical Communications and Surveillance
www.cobham.com/tcs
On the bench make sure to use a 20 dB attenuator rated for 2W (or more).
1.5.
HEATSINK
Use an adequate heat-sink to keep the base plate temperature of the PA below 70
O
C (149 F).
For operation in extreme conditions or under direct sun exposure larger heat-sink and/or forced cooling
will be required. An over temperature detector sticker is applied externally and internally to the PA.
The sticker has five white dots which turn black when the temperature reaches 60, 65, 71, 77, 82
O
C.
(140, 149, 160, 171, 180 F). A black 71
O
C. (160 F) dot will void the warranty.
1.6.
RF OVERDRIVE
The PA is designed to operate at up to 2W with COFDM signals having PAR ratios up to 14 dB. To
achieve the best efficiency the PA operates at the highest power that will allow the desired linearity
without damaging the devices. Therefore it is important not to overdrive the PA or damage might
occur.
This PA will survive and continue to operate with
a momentary 2-3 dB overdrive. Higher overdrives will
trigger the protection circuit opening an internal RF switch which disconnects the RF input from the
rest of the circuit. The switch will remain in an open latched condition until the overdrive input is
removed 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). This circuit will provide a certain level of
protection from accidental overdrives. High and sudden overdrives will damage the PA and therefore all
care should be taken to avoid overdrive conditions. The operator should carefully set the input power
before connecting to the PA. During set up it is recommended that the output power be monitored
with a power meter.
1.7.
OVER TEMPERATURE AUTOMATIC SHUTDOWN
The VEPA-2W is designed and specified to operate up to a maximum of 70°C baseplate temperature.
Operating the PA at higher temperatures than specified can damage the PA or cause the MTTF to drop
significantly. The VEPA-2W incorporates an over-temperature automatic shutdown feature. When the
baseplate temperature reaches ~75°C the PA will toggle to standby mode (~110mA current draw at
12Vdc) until the baseplate temperature drops below 70°C at which point the PA will resume normal
operation (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 2 (PIN1) will
toggle logic high). No power cycle is required, although the operator should take steps to better heat-
sink the VEPA-2W if the protection state is reached during normal operation.
1.8.
POWER MEASUREMENT
Using a reliable power meter is recommended for initial power set up. Choose a power head that can
handle the power to be measured. In most cases you will need to connect a suitable attenuator
between the PA RF output port and the Power meter. Using in-line power meter is not recommended
especially with antennas for initial set up because an antenna will create a standing wave. The power
meter readings will vary depending on the position of the power meter in the line and therefore it is
possible to have readings lower or higher than the actual power delivered by the PA.