funcube payload specification · web viewon/off switching interface between the cct board and...

FUNcube PA Board Specification

Doc-ID: Date: Issue: Page:

FUNcube.PA_Board.doc17th December 20110.5 DRAFT1


SummaryThis 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: FUNcube Project management onlyFUNcube Technical team only

X Unlimited public release

Keywords: FUNcube, payload, specificationDocument-ID:

Issue: 0.5 DRAFT Issue:Date: 17th December 2011

Prepared: DBRevised: GPS/DB

Checked: Gps/dbApproved:

© 2023 AMSAT-UK




Revision Record

issue date totalpages

Authorisation affectedpages

brief description of change

0.1a DRAFT 01.07.10 DB all Initial draft0.2 Draft 14.09.10 DB Most General updates / TBDs defined0.3 draft 18.09.10 DB Small corrections0.4 draft 15.11.10 DB General updates and additional

info0.5 draft 10.12.11 DB most Updates reflecting design and

outline changes. Inclusion of development history in lieu of design justification document.

List of TBD’s and TBC’sNil

List of abbreviations and Acronyms

AIV – Assembly integration and verificationEPS – Electrical power systemRF – Radio FrequencyFM – Flight modelEM – Engineering modelGSE - Ground Support EquipmentTBC – To be confirmedTBD – To be decidedPA – Power amplifierMPPT – Maximum power point tracker

© 2023 AMSAT-UK




Table of Content

Summary.....................................................................................................................................11. Introduction........................................................................................................................42. Payload Specifications........................................................................................................4

2.1 Functional Description & Block Diagram........................................................................42.2 The Circuit Diagram of the PA Board..............................................................................62.3 PCB and Overlay............................................................................................................72.4 Operational specifications............................................................................................102.5 Performance specifications..........................................................................................102.6 Interfaces.....................................................................................................................112.7 Radiated & susceptible frequencies.............................................................................122.8 Failure mitigation strategy...........................................................................................122.9 Handling and Storage procedures................................................................................122.10 Testing.........................................................................................................................132.11 Ground support equipment..........................................................................................13

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1. IntroductionThe 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 Specifications2.1 Functional Description & Block DiagramThe PA Board provides the following functions:

1) Linear amplification of minimum value of 12dB at 145.9 MHz for signals from the RF board

2) Output low pass filtering with traps at the 3rd harmonic3) Telemetry output via an I2C interface of:

Forward RF output powerReflected RF output powerDC input current to the final RF amplifierTemperature 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 TelemetryTelemetry 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.

© 2023 AMSAT-UK




DC current to the amplifier is measured with a Texas INA194. The 194 circuit includes an R/C a filter so the 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 16VEach 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.”

© 2023 AMSAT-UK




2.2 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 OverlayThe 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.

© 2023 AMSAT-UK




2.4 Operational specificationsGain. 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 Performance specifications

2.5.1 Power ConsumptionThe 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 linearityThe 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 DissipationThe 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 MassThe 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.

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2.5.5 Mechanical envelopeThe components project 11mm above the board and 3 mm below. The 11mm is limited by the height of the PC104 connector.

2.5.6 Supply voltageThe 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 currentThe inrush current shall be limited to be compatible with the current output available from the EPS Bat Buss output.

2.6 Interfaces

2.6.1 MechanicalThe PA board shall be supported by the structure at 4 fixings points. It gains additional support from the PC104 interconnection headers.

2.6.2 RFThe 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 PowerThe power amplifier board receives power from the PC104 connector.

3V3 via H2 pins 27 & 285V via H2 pins 25 & 26Bat bus (6.2 – 8.2V) via H2 pins 46 &47Ground / Zero volts via H2 pins 29, 30 & 32

2.6.4 DataA bidirectional serial data line for the I2C communication is provided on the PC104.I2C clock is on H1 pin 43I2C 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 0110100I2C isolators / repeaters are not used.

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2.7 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 3rd 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 strategyThe 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 TestingThe 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 +/- 1dB2) RF output level in safe mode – 9dB on Educational mode3) Bias point set to 20mA +2mA -1mA4) RF spectrum checked for harmonics and compared to lab results > -70dB5) RF spectrum checked for IMD at high power. 2 tone test. 3rd order > -26dB6) 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 equipmentFor 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

© 2023 AMSAT-UK

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