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FUNcube PA Board
Specification
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FUNcube PA Board Specification
Summary
This document provides the specification for the PA Board which forms part of the educational
payload as designed by the AMSAT-UK FUNcube technical team.
Distribution:
X
FUNcube Project management only
FUNcube Technical team only
Unlimited public release
Keywords: FUNcube, payload, specification
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Date: 17th December 2011
Prepared: DB
Revised: GPS/DB
Checked: Gps/db
Approved:
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FUNcube PA Board
Specification
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Revision Record
issue
date
0.1a DRAFT
total
pages
Authorisation
affected
pages
01.07.10
DB
all
0.2 Draft
14.09.10
DB
Most
0.3 draft
18.09.10
DB
Small corrections
0.4 draft
15.11.10
DB
General updates and additional
info
0.5 draft
10.12.11
DB
List of TBD’s and TBC’s
Nil
List of abbreviations and Acronyms
AIV – Assembly integration and verification
EPS – Electrical power system
RF – Radio Frequency
FM – Flight model
EM – Engineering model
GSE - Ground Support Equipment
TBC – To be confirmed
TBD – To be decided
PA – Power amplifier
MPPT – Maximum power point tracker
© 2017 AMSAT-UK
most
brief description of change
Initial draft
General updates / TBDs defined
Updates reflecting design and
outline changes. Inclusion of
development history in lieu of
design justification document.
FUNcube PA Board
Specification
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Table of Content
Summary ............................................................................................................................................. 1
1.
Introduction .................................................................................................................................. 4
2.
Payload Specifications .................................................................................................................... 4
2.1
Functional Description & Block Diagram...................................................................................... 4
2.2
The Circuit Diagram of the PA Board .......................................................................................... 6
2.3
PCB and Overlay ....................................................................................................................... 7
2.4
Operational specifications ........................................................................................................ 10
2.5
Performance specifications ...................................................................................................... 10
2.6
Interfaces ............................................................................................................................... 11
2.7
Radiated & susceptible frequencies .......................................................................................... 12
2.8
Failure mitigation strategy ....................................................................................................... 12
2.9
Handling and Storage procedures ............................................................................................ 12
2.10 Testing ................................................................................................................................... 13
2.11 Ground support equipment ...................................................................................................... 13
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Specification
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1. Introduction
The FUNcube payload comprises of multiple boards. Each board is a “standard” cubesat board with a
cubesat bus interface and other connections as required. These are detailed in the Interface Control
Document
This is the document for the PA board. The PA board provides final frequency amplification for the
transmitter and also provides smoothing for the main battery bus using multiple capacitors.
Additionally it provides space on the earth plane for the names or callsigns of the supporters of FUNcube to
be recorded.
2. Payload Specifications
2.1
Functional Description & Block Diagram
The PA
1)
2)
3)
Board provides the following functions:
Linear amplification of minimum value of 12dB at 145.9 MHz for signals from the RF board
Output low pass filtering with traps at the 3rd harmonic
Telemetry output via an I2C interface of:
Forward RF output power
Reflected RF output power
DC input current to the final RF amplifier
Temperature of the final RF amplifier
4) Energy storage for the EPS Battery Bus output. (requirement removed 4/11)
5) Interconnection from the EPS to the other satellite boards via a PC104 connector.
6) On/off switching interface between the CCT board and the DC supply to the power amplifier using
3v3 logic.
2.1.1
RF Amplifier and filtering
The RF amplifier is a single stage class AB amplifier using a Mitsubishi RD02MUS1 power MOS FET.
The amplifier is biased to 20mA quiescent current at the nominal maximum battery voltage of 8.2 Volts. The
biasing is set by fixed resistors feeding a current through two diodes bonded to the top of the FET. The
diodes provide thermal tracking as the satellite cycles through its expected temperature range. To thermally
compensate the RD02MUS1 a silicon diode and a schottky diode will be connected in series. This
combination provides apx. –3.4mV per degree tracking which closely matches the positive coefficient of the
PA device. The PA shall be capable of operating into undeployed antennas at nominal temperature ranges
without failure.
Output filtering is achieved with a 5 element Chebyshev low pass filter with the series coils resonated by
parallel capacitors to provide notches at the 3rd harmonic.
2.1.2
Telemetry
Telemetry of 4 values is achieved with a MAXIM MAX11607 4 channel analogue to digital converter with
serial I2C interface. The telemetry system is powered by the regulated 3V3 EPS output. Each of the 4
sensors used give a voltage output which is dependent on the quantity being measured.
DC current to the amplifier is measured with a Texas INA194. The 194 circuit includes an R/C a filter so the
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telemetry value measures the average current not the instantaneous value.
Forward and reflected power is detected with a bi-directional coupler with a coupling factor of 20dB. Each
coupled RF output is fed to an AD8361 power detector. A small series attenuator is used to set the level to
the optimum value for the AD8361. The attenuator is used on both outputs because the reflected power
sensor will have a high level output (Hi VSWR) while the antennas are inside the cubesat deployer.
2.1.3
Energy storage (requirement removed 4/2011.)
The original requirement for energy storage was removed in mid 2011 when it became clear that the
proposed technique was incompatible with the design of the Clydespace EPS. The concept description is
retained below, with the proposed circuit, for design justification purposes. However, when implemented it
was found that:
1) While the total capacitance was adequate to keep the battery bus supply from dropping below 5.8V
during MPPT 125ms outages, The EPS battery protection circuit activated at 6.2V causing a master
system reset.
2) Additional capacitance up to 100,000uF was added externally to increase the storage capacity. At
these increased capacitance levels, the switched mode converter used in the BCRs oscillated.
It was concluded that the only viable methods would be to modify the EPS or bypass the BCRs with an
external boost converter after the battery had failed. Neither option was considered practical and the
decision was made to fly the Clydespace EPS as supplied.
Original 2.1.3 entry
“The PA board includes 5 banks of capacitors which are used to store charge. While in nominal mission,
when the batteries remain functional, the capacitors are not used. However, should the batteries fail open
circuit, then the capacitors are necessary to supply current to the satellite during the 124ms period when the
MPPT disconnects the solar cells from the BCR. (See Clydespace manual). The capacitors are arranged into
5 banks of 5 x 220uF tantalums. Total value is 5500uF at 16V
Each bank is fitted with a series resistor in parallel with a schottky diode. When charging, the current flows
via the resistors which limit the inrush current. This allows the capacitors to fully charge over the 2 seconds
between each MPPT disconnect. The resistor power rating and value are selected to allow the resistor to
burn out (open circuit) should one or more of the capacitors fail short circuit. – Note this will only happen
while the battery retains charge. i.e. The resistors protect the satellite during nominal mission.
The schottky diode allows the capacitors to transfer energy into the satellite systems efficiently without
loosing energy due to I2R losses. The forward voltage lost due to the diode is 350mV.”
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The Circuit Diagram of the PA Board (original with storage capacitors)
The circuit above was superseded in April 2011.
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The circuit above is the final iteration used to produce the FUNcube EM and FM hardware. The storage
capacitors have been removed and high value ceramics have been added to some telemetry lines.
2.3
PCB and Overlay
The circuit has been implemented on a double sided 1.6mm FR4 PCB with plated through holes. There have
been 3 versions produced.
a) Prototype and UKube EM. Uses energy storage capacitors. Manufactured in China. Some observed
effects which could lead to delamination under high temperature conditions.
b) Manufactured by PCB Pool in Ireland. New board outline for UKube compatibility providing cut-outs
for interboard wiring. Energy storage removed. Revised position of input MCX connector for easier
cable routing from RF board.
c) Flight model for FUNcube and UKube. Same as b above but with high tg board material.
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The original layout below (a above) shows the positions of the major components. This is a top view. Red
track is top copper, blue tracks are bottom copper. Top and bottom ground planes and silk screen are also
shown.
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Flight model outline and component overlay.
The layout below shows the FM board. This overlay shows component locations, however these have not all
been printed onto the FM board to avoid outgassing. – Conformal coating has not been used. The IPR
statement has been reproduced for EM and FM hardware.
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Specification
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Operational specifications
Gain. Input to the amplifier from the RF board is +15dBm. Maximum designed RF output of the PA is
+27dBm or 500mW Peak envelope power. Therefore the required gain of the completed board is 12dB at
8.2 Volts. Should the gain of the amplifier be higher than 12dB then either the input level from the RF board
can be reduced, or an appropriate resistive pad can be fitted to the spaces provided at the input of the PA
board
Bandwidth. The –3dB bandwidth shall be a minimum of 6 MHz.
2.5
2.5.1
Performance specifications
Power Consumption
The quiescent power consumption of the amplifier with no input signal is 20mA @ 8.2V or 164mW.
The quiescent power level of the peripheral components (I2C op-amp buffer and power detectors) is less
than or equal to 10mW.
The total is 174mW.
At 500mW PEP output the target power added efficiency is 50% or better.
At the minimum efficiency the DC input shall be 1000mW+174mW = 1174mW or at 8.2V = 143mA peak
2.5.2
Radiated power and linearity
The maximum DC input power to the FUNCube PA board is 1174mW. At minimum efficiency the RF output
will be 500mW when connected to a 50 ohm load leaving 674mW to be dissipated as heat.
The amplifier is designed to allow 3rd order inter-modulation distortion not higher than –26dB below each
tone in a two tone test. This value shall be achieved with the supply voltage at 7.2 to 8.2 volts. Linearity
may degrade below this range of supply voltages.
2.5.3
Heat Dissipation
The maximum power to be dissipated under normal operating conditions* is 674mW.
This will be dissipated by conduction through the Earth planes and by radiation from the board and by
conduction via the structure and radiation from other parts of the spacecraft.
*Should the 145MHz antennas fail to deploy, or during periods of testing, then the full DC input to the PCB
will be dissipated as heat. This figure in mW will be determined during testing as the performance of the PA
will be considerably different when connected to the highly reactive load of an undeployed antenna.
2.5.4
Mass
The total PA board is 54g.
This does not include the 2 RF MCX plugs and harness necessary to connect the board to the antennas and
RF board.
2.5.5
Mechanical envelope
The components project 11mm above the board and 3 mm below. The 11mm is limited by the height of the
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PC104 connector.
2.5.6
Supply voltage
The bus voltage shall be between the maximum and minimum voltages supplied by the EPS. (6.2 – 8.2V)
The supply voltage with RF drive shall not exceed 9.0 Volts. The PA transistor shall survive transients to 12V
but without RF drive.
2.5.7
Inrush current
The inrush current shall be limited to be compatible with the current output available from the EPS Bat Buss
output.
2.6
2.6.1
Interfaces
Mechanical
The PA board shall be supported by the structure at 4 fixings points. It gains additional support from the
PC104 interconnection headers.
2.6.2
RF
The 145MHz input from the RF board and the output to the antenna deployment module shall be via MCX
right angle sockets. The MCX type selected is the Amphenol MC-625261-3GT59G-50 – RS Components part
Number 700-9521.
2.6.3
Power
The power amplifier board receives power from the PC104 connector.
3V3 via H2 pins 27 & 28
5V via H2 pins 25 & 26
Bat bus (6.2 – 8.2V) via H2 pins 46 &47
Ground / Zero volts via H2 pins 29, 30 & 32
2.6.4
Data
A bidirectional serial data line for the I2C communication is provided on the PC104.
I2C clock is on H1 pin 43
I2C data is on H1 pin 41
The PA board I2C is configured as a slave device. The board receives requests for data to be transferred
from the CCT board which contains the I2C master. The slave address for the MAX11607 is fixed at 0110100
I2C isolators / repeaters are not used.
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Specification
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Radiated & susceptible frequencies
The PA board generates high levels of RF energy at 145.9 MHz. It also has harmonic content shall be filtered
from the output prior to being sent to the antenna system. Failure to reduce the level of harmonics at the
output will desense the receiver on the RF board. Direct radiation of 3 rd harmonic from components within
the PA output network or filter may occur. The design and location of the receiver should be considered to
minimise the risk of interference due to proximity to a potential source of interference.
The PA board is not susceptible to signals generated elsewhere in FUNcube.
2.8
Failure mitigation strategy
The PA board contains numerous single point failure risks. However, the major risk assessment is from
cracking or other physical damage to surface mount components due to the lack of support in the centre of
the PCB. This risk within the telemetry gathering circuits is accepted. The risk within the amplifier circuit
shall be mitigated by:
1)
Critical series components in the amplifier circuit shall be either leaded components or
formed from two SMD components in parallel.
2)
Capacitors forming matching or filtering functions shall be formed from two or more
components in parallel.
3)
The PA_ON control line from the CCT board shall use an on board pull-up resistor. This shall
cause the PA default to PA ‘on’ in the event of an open circuit in the PC104 headers.
2.9
Handling and Storage procedures
2.9.1 Handling
Note that the PA Board is sensitive to Electro Static Discharge (ESD).
Whenever handling the PA Board make sure to follow the following directives:
· Always wear gloves when handling the PA Board to prevent contamination
· Handle the PA Board in an ESD protected environment (bench mat, wrist strap)
· Do not handle the PA Board with any active power supply
· For the Flight Model limit the number of connector mating cycles to less than 50.
· Ensure over-current and over-voltage protection are present when connecting to external
power supplies.
· Handling technique shall avoid flexing the PCB
2.9.2 Storage
· Store the PA Board in an ESD bag with a silica gel bag
· Storage temperature: +5 to +25°C (RH<50%)
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2.10 Testing
The following tests shall be carried out during qualification level testing on the engineering model and at
acceptance level on the flight model hardware:

Functionality between tests.
1) RF output in safe mode (-9dB) and high power in educational mode.
2) Telemetry from all 4 sensors produced on I2C. Decoded values compared to baseline values.
3) Bias point at Iq =20mA.

Performance after completion of vibration and thermal vacuum tests.
1) RF output level in educational mode +27dBm PEP +/- 1dB
2) RF output level in safe mode – 9dB on Educational mode
3) Bias point set to 20mA +2mA -1mA
4) RF spectrum checked for harmonics and compared to lab results > -70dB
5) RF spectrum checked for IMD at high power. 2 tone test. 3rd order > -26dB
6) Telemetry tests. a) PA temp changes from cold start
b) PA current changes from Safe to EDU modes
c) RF forward power safe / EDU modes
d) RF rev power. Apply 10:1 SWR for 10 seconds.
7) Reactive load test. The PA shall be operated into undeployed antennas for a period of 5 minutes
starting from 25 degrees. PA current and PA temp shall be recorded at the start and finish of the test. (t=5
and t=290s). Following the test the PA shall be operated into a 50 ohm load and performance compared to
prior results.

Following successful vibe/thermal vac testing, the telemetry shall be calibrated on the FM hardware
as part of the AIV process. Telemetry equations to be derived and made available to ground station
team for own use and onward distribution to educational / amateur community as appropriate.
2.11 Ground support equipment
For the PA board, the following GSE is required:
For functional checkout before integration:
 Fully functioning RF Board
 Power supplies (3V3, 5V and 8V)
 104 pin connector pin savers
 RF connector pin savers
 50ohm 2W dummy load
 Test antennas for VHF and UHF
 VHF/UHF full duplex SSB transceiver
 Spectrum analyser
For functional checkout after integration:
 VHF/UHF full duplex SSB transceiver
 Ground station command transmit and calibrated telemetry receiving software
 Spectrum analyser
© 2017 AMSAT-UK