COBHAM VEPA-2W User manual

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Cobham Tactical Communications and Surveillance
1916 Palomar Oaks Way, Suite 100, Carlsbad, CA 92008
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GMS Inc. doing business as Cobham Tactical Communications and Surveillance www.cobham.com/tcs
Technical Operations Manual
The most important thing we build is trust.
VEPA-2W Linear Power Amplifier

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REVISION HISTORY
Version Date Author Comments
X1 10/01/11 Nathan Moore / Marcio Koptcke Initial release.
X2 02/15/12 Nathan Moore Release to include C2 Band

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TABLE OF CONTENTS
1.CAUTIONS AND WARNINGS......................................................................................................................................................5
1.1.ELECTROMAGNETIC RADIATIONS ................................................................................................................................................. 5
1.2.SUPPLY VOLTAGE AND CURRENT.................................................................................................................................................... 5
1.3.PA ENABLE (Fast Switching)................................................................................................................................................................. 5
1.4.RF LOAD TERMINATION (50 Ohm)ΩΩ ....................................................................................................................................... 5
1.5.HEATSINK.......................................................................................................................................................................................................... 6
1.6.RF OVERDRIVE ............................................................................................................................................................................................... 6
1.7.OVER TEMPERATURE AUTOMATIC SHUTDOWN.................................................................................................................. 6
1.8.POWER MEASUREMENT.......................................................................................................................................................................... 6
2.ABSOLUTE MAX RATINGS............................................................................................................................................................7
3.SPECIFICATIONS................................................................................................................................................................................7
4.POWER AMPLIFIER FEATURES.................................................................................................................................................9
4.1.MODE OF OPERATIONS ........................................................................................................................................................................... 9
4.1.1.HIGH LINEARITY MODE (OR HIGH MER MODE).......................................................................................................... 9
4.1.2.HIGH EFFICIENCY MODE (OR LOW CURRENT MODE) ............................................................................................ 9
4.2.PA ENABLE (Fast Switching Capable)............................................................................................................................................. 9
4.3.VSWR, RF OVERDRIVE AND OVER-TEMERATURE PROTECTION CIRCUITS ...................................................... 9
5.OPERATIONAL INSTRUCTIONS ............................................................................................................................................10
5.1.EXTERNAL CONNECTIONS................................................................................................................................................................. 10
5.2.CONNECTING & DISCONNECTING THE POWER AMPLIFIER.................................................................................... 11
5.3.APPLICATION EXAMPLES ................................................................................................................................................................... 11
5.3.1.BASIC CONFIGURATION ........................................................................................................................................................... 11
5.3.2.VEPA-2W / VMT COMBINATION .......................................................................................................................................... 13
5.4.USING A TRANSMITTER / PA COMBINATION .................................................................................................................... 13
5.4.1.The old FM approach .................................................................................................................................................................... 13
5.4.2.The NEW Digital Modulation approach ........................................................................................................................... 14
6.TYPICAL POWER AMPLIFIER PERFORMANCES .........................................................................................................16
6.1.GAIN @ 2W COFDM Output .............................................................................................................................................................. 16
6.2.Current @ 2W COFDM Output, 12 Vdc....................................................................................................................................... 18
6.3.MER @ 2W COFDM Output................................................................................................................................................................. 19
6.4.Small Signal S-Parameter (High Efficiency Mode).............................................................................................................. 20
LIST OF TABLES
Table 1 – ABSOLUTE MAX RATINGS .............................................................................................................................................7
Table 2 – General Specifications: .....................................................................................................................................................7
Table 3 – Frequency Specific Specifications: ..........................................................................................................................8

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LIST OF FIGURES
Figure 1 – VEPA-2W PA External Connections....................................................................................................................10
Figure 2 – PA on small Heat-sink with Test Cable and Isolator (Isolator Optional) ................................12
Figure 3 – VEPA-2W PA with VMT................................................................................................................................................13
Figure 4 – LD Band Gain.......................................................................................................................................................................16
Figure 5 – LD Band Gain Change over Temp .........................................................................................................................16
Figure 6 – L2 Band Gain........................................................................................................................................................................16
Figure 7 – L2 Band Gain Change over Temp..........................................................................................................................16
Figure 8 – W7 Band Gain .....................................................................................................................................................................16
Figure 9 – W7 Band Gain Change over Temp .......................................................................................................................16
Figure 10 – S2 Band Gain ....................................................................................................................................................................16
Figure 11 – S2 Band Gain Change over Temp ......................................................................................................................16
Figure 12 – SK Band Gain ....................................................................................................................................................................16
Figure 13 – SK Band Gain Change over Temp ......................................................................................................................16
Figure 14 – C2 Band Gain....................................................................................................................................................................17
Figure 15 – C2 Band Gain Change over Temp......................................................................................................................17
Figure 16 – LD Band Current.............................................................................................................................................................18
Figure 17 – L2 Band Current .............................................................................................................................................................18
Figure 18 – W7 Band Current...........................................................................................................................................................18
Figure 19 – S2 Band Current.............................................................................................................................................................18
Figure 20 – SK Band Current.............................................................................................................................................................18
Figure 21 – C2 Band Current.............................................................................................................................................................18
Figure 23 – L2 Band MER.....................................................................................................................................................................19
Figure 24 – W7 Band MER ..................................................................................................................................................................19
Figure 25 – S2 Band MER ....................................................................................................................................................................19
Figure 26 – SK Band MER ....................................................................................................................................................................19
Figure 29 – L2 Band S-Parameters................................................................................................................................................20
Figure 30 – W7 Band S-Parameters..............................................................................................................................................20
Figure 31 – S2 Band S-Parameters................................................................................................................................................20
Figure 32 – SK Band S-Parameters ...............................................................................................................................................20
Figure 33 – C2 Band S-Parameters ...............................................................................................................................................20
APPENDICES
APPENDIX 1 - ACRONYMS .................................................................................................................................................................21
REFERENCES
( 1 ) MIL-STD-810 Department of Defense Test Method Standard for Environmental Engineering
Considerations and Laboratory Tests

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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.

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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 OC (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 OC.
(140, 149, 160, 171, 180 F). A black 71 OC. (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.

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2. ABSOLUTE MAX RATINGS
Table 1 – ABSOLUTE MAX RATINGS
MAX MOMENTARY RF INPUT COFDM 6 dBm
MAX SUPPLY VOLTAGE 35 Vdc
MAX CONTINUOS COFDM PWR 2 W
MAX CONTINUOUS FM PWR 3 W
MAX PA_ENABLE VOLTAGE 6.5 Vdc
CAUTION: 2-3 dBm is the typical input PWR for operation at 2 W. The PA will survive a momentary 3 dB
overdrive. Larger overdrives will trigger the protection circuit (see section 4.2)
3. SPECIFICATIONS
Table 2 – General Specifications:
Parameter Specification
DC input voltage (Vdc) 9-32
Mechanical Dimension
(without heat-sink)
2.1 "L x 3.0 "W x 0.6 "H
5.3 cm x 7.6 cm x1.52 cm
Weight lbs 0.300
grams 136
Base-plate Temperature -20 °C to + 70 °C
Operating Humidity 95% Non-condensing
Control Connector (Header)
9pin 1.25mm JST
SM09B-GHS-TB
FAULT 2 PIN 1
FAULT 1 PIN 2
MODE SELECT PIN 3
+5 VDC (OUTPUT) PIN 4
PA ENABLE (3-5Vdc) PIN 5
Vcc (9-32Vdc) PIN 6
Vcc (9-32Vdc) PIN 7
GND PIN 8
GND PIN 9
RF Connectors SMA female
NOTES:
To select High Efficiency MODE (LOW CURRENT) leave Pin 3 open.
To select High Linearity MODE (HIGH MER) connect Pins 3 and 4. Or connect 3-5 Vdc to Pin3.
PA ENABLE is LVTTL compatible.
Pins 8 and 9 are internally connected to chassis.

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Table 3 – Frequency Specific Specifications:
Parameter Specification
Frequency (GHz) 1.4 - 1.6 1.7 - 1.85 1.7 - 2.4 1.99 - 2.5 2.2 - 2.4 2.2 - 2.7 4.4 – 5.0
Frequency Band LD L2 W7 S2 S1 SK C2
HIGH EFFICIENCY
MODE1: MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX
Liner Gain (dB) 29.0 30.3 31.7 29.8 30.6 31.1 28.5 29.7 30.8 29.0 30.2 30.9 29.8 30.5 30.9 29.2 30.5 31.6 29.3 30.7 32.8
Flatness (dB) +/- 1.3 +/- 1.5 +/- 0.7 +/- 0.8 +/- 1.2 +/-
1.4 +/- 1.0 +/- 1.1 +/- 0.5 +/-0.6 +/- 1.2 +/- 1.3 +/- 1.3 +/- 1.6
Current @12 Vdc on
50 Load (A) 1.06 1.15
0.96 1.04 1.1 1.28 1.04 1.17 1.0 1.08 0.97 1.01 1.07 1.11
MER (dB)221.7 28.0 25.3 26.9 19.3 21.9 21.0 23.0 22.2 23.4 19.7 22.8 22.6 25.1
EVM (%)34.0 8.2
4.5 5.4 8.0 10.8 7.1 8.9 6.8 7.8 7.2 10.4 5.5 7.4
ACPR (-dB) 22.5 29.0 26.2 27.8 20.1 22.7 21.8 23.9 23.0 24.3 20.5 23.6 27 29.5
HIGH LINEARITY MODE1: MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX MIN AVERAGE MAX
Liner Gain (dB) 28.7 30.1 31.8 29.4 30.6 31.6 28.7 30.2 31.5 29.7 31.0 31.8 30.8 31.3 31.8 29.2 31 32.5 30.8 32.3 34.3
Flatness (dB) +/- 1.2 +/- 1.4 +/- 0.6 +/- 0.7 +/- 1.1 +/-
1.2 +/- 0.8 +/- 0.9 +/- 0.5 +/- 0.6 +/- 1.0 +/- 1.1 +/- 1.4 +/- 1.7
Current @12 Vdc on
50ΩLoad (A) 1.33 1.44
1.18 1.28 1.32 1.52 1.25 1.4 1.2 1.3 1.15 1.22 1.32 1.39
MER (dB)227.3 29.9 29.1 30.5 25.2 26.2 26.0 27.2 26.5 27.2 24.6 26.7 26.3 28.7
EVM (%)33.2 4.3 3.0 3.5 4.9 5.5 4.4 5.0 4.4 4.7 4.6 5.9 3.7 4.8
ACPR (-dB) 28.5 31.0 30.0 32.1 26.2 27.3 27.1 28.5 27.3 28.5 25.5 27.8 30.5 33
Input RL (dB) -25 -20 -20 -14 -14.7 -9.6 -12.3 -9.6 -12.3 -9.6 -16 -10.5 -13 -12
Output RL (dB) -17 -12 -17 -12 -17.3 -9.6 -15.5 -10 -15.5 -10 -15.8 -10 -19 -15
Harmonic (dBm /MHz) -29 -25 -35 -29 -37 -24 -40 -31 -45 -37 -40 -32 -34 -23
Gain Change (dB) (Over
Temperature -20 to 70 °C +/- 0.25 +/- 0.5 +/- 0.25 +/- 0.5 +/- 0.25 +/-
0.5 +/- 0.25 +/- 0.5 +/- 0.25 +/- 0.5 +/- 0.25 +/- 0.5 +/- 1.25 +/- 1.5
Standby Current @ 12 Vdc
(A) (PA_ENABLE = 0V) 0.11 0.12 0.11 0.12 0.11 0.12 0.11 0.12 0.11 0.12 0.11 0.12 0.08 0.12
Switching Speed TON (ns) 90 100 90 100 90 100 90 100 90 100 90 100 150 160
Switching Speed TOFF (ns) 40 50 40 50 40 50 40 50 40 50 40 50 100 110
RF Isolation (PA_ENABLE
= 0Vdc) (dB) 65 70 65 70 65 70 65 70 65 70 65 70 65 70
Notes:
1. Measurements performed at 2 W output power (33 dBm), PA_ENABLE = 3.0Vdc
2. MER measurements were performed using a Rhode & Schwartz EFA Test RCVR mod 2067 in Stationary mode. DVB-T test signal generated with an Agilent MXG Vector Signal Generator.
3. EVM specification valid for QPSK modulation only.

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4. POWER AMPLIFIER FEATURES
4.1. MODE OF OPERATIONS
The VEPA-2 W amplifier was designed to give the best possible combination of Linearity and Efficiency.
There are applications where High Linearity is required (i.e. 64 QAM) and applications where lower
linearity is acceptable and High Efficiency is more important (e.g. 16 QAM and QPSK). The VEPA-2W
amplifier allows the operator to select the preferred mode of operation by external cable (cable can be
provided with jumpers installed according to the desired operation mode) or by installing jumpers in
the connector.
4.1.1. HIGH LINEARITY MODE (OR HIGH MER MODE)
To select this mode jumper pin 3 to pin 4. This will result in higher linearity with approx. 200 mA
increase in current (at 12 Vdc).
4.1.2. HIGH EFFICIENCY MODE (OR LOW CURRENT MODE)
To select this mode simply leave pin 3 of the connector open. This will result in a current about
200mA lower than the high linearity mode and about 2-3 dB decrease in MER when operating at
2W full power. There is almost no MER penalty when operating at 1W. Therefore for operation at
1W or lower the best MODE of operation is the HIGH EFFICIECNCY MODE
4.2. PA ENABLE (Fast Switching Capable)
The VEPA-2 W amplifier was designed have a LVTTL compatible enable pin (PIN 5). The VEPA-2W was
designed for fast switching applications with an ON time <100ns and an OFF time of <50ns (For C2
band: ON time <150ns and an OFF time of <100ns). To achieve this fast switching functionality the PA
will draw a small bias current when in standby (PA_ENABLE = 0V or LVTTL logic low), less than 120mA.
The VEPA-2W has >65dB isolation when in standby mode.
4.3. VSWR, RF OVERDRIVE AND OVER-TEMERATURE PROTECTION CIRCUITS
The VEPA-2W amplifier implements a circuit which senses VSWR and overdrive. When the RL of the
load is lower than 7-8 dB and/or when the input overdrive exceeds 3 dB the protection circuit triggers a
RF switch placed in series with the RF input line (VSWR protection is not available in C2 band VEPA).
The switch remains open until the faulty condition is removed and the DC input power is cycled OFF
and ON. In Normal operation the green LED (see fig. 1) is ON. When the RF switch opens the LED color
turns red, as well as the FAULT 1 (PIN2) toggling logic high.
CAUTION: The protection circuit increases the chances for the PA to survive excessive VSWR and/or
overdrive is NOT 100% protection in all cases. An output mismatch that occurs at the output port
because the antenna match is degraded (poor antenna, antenna degraded by rain, antenna placed in
proximity of metal objects etc.) will likely trigger the protection circuit and protect the amplifier from
damage. But a sudden open or short at full power could damage the amplifier. Similarly the protection

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circuit will be effective in protecting from limited overdrives. Sudden large overdrives will damage the
amplifier.
The VEPA-2W also incorporates an OVER TEMPERATURE PROTECTION circuit. This circuitry operates
slightly differently than the VSWR and OVERDRIVE protection in that it does not need a power cycle to
correct. The OVER TEMPERATURE shutdown will allow normal operation when the VEPA-2W baseplate
temperature has dropped by 5°C from the trip point of 75°C. In Normal operation the green LED (see
fig. 1) is ON. When the RF switch opens the LED color turns red, as well as the FAULT 2 (PIN2) toggling
logic high. If this fault is being toggled during normal operation of the amplifier, the operator needs to
take steps to improve the heat-sinking of their system.
5. OPERATIONAL INSTRUCTIONS
Read this section carefully and the section in Section 1 (CAUTIONS AND WARNINGS)
before operating the Power Amplifier.
5.1. EXTERNAL CONNECTIONS
Figure 1 – VEPA-2W PA External Connections
9 pin 1.25mm JST I/O
SM09B-GHS-TB
RF OUT
Antenna Port
MODE
RF INPUT
GREEN LED
DC PWR indicator
and protection circuit
status