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PA88108 Series

Asia Pacific | EMEA | Americas 1

User’s Manual

PA88108

100w Linear RF Amplifier

87.5-108MHz

Base Line 1.01

Document Number: INS-41970-3

INS-41970-3 PA88108 User’s Manual


Company Overview

RFI has been serving the needs of the wireless communications market for over 30 years. First founded as a manufacturer of antenna systems, RFI has grown to be a key player in the development, manufacturing and distribution of wireless technology and energy products. Through our extensive network of resellers, systems integrators and retail outlets, RFI is a key supplier to both industry and Government. Our research and manufacturing facilities have talented people, sophisticated test equipment, state of the art software with class leading manufacturing systems and techniques. Additionally, we have in place a quality management program which is certified to ISO9001, environmental management system certification to ISO14001 and occupational health and safety standard AS4801 giving you complete confidence in everything we do. RFI’s products are truly innovative and as a result we are active around the globe taking our Australian designed and manufactured products to key markets in Asia Pacific, the Americas and EMEA regions via offices ‘In-region’ in addition to exporting directly to in excess of 50 countries. One of RFI’s key principals is to remain totally customer focused as we recognise our future depends on the success of our customers. We know that to be chosen as your supplier we must add value to your business and to achieve this we will work hard to deliver the best product when and where you need it and back this up with the very best technical support available.



Document Number INS-41970-3

Copyright 2015 RF Industries Pty Ltd First Printing: 18

th February 2015

Version Number

Version Date

DRAFT 18th February 2015

Disclaimer

Product part numbering in photographs and drawings is accurate at the time of printing. Part number labels on RFI products supersede part numbers given within this manual. Information is subject to change without notice.



TABLE OF CONTENTS

1. GENERAL DESCRIPTION .............................................................................................................. 7

1.1 Structure .............................................................................................................................. 7 1.2 Features ............................................................................................................................... 7 1.3 Block Diagram .................................................................................................................... 7 1.4 Brief Description ................................................................................................................. 8 2. Specifications ............................................................................................................................ 9

3. ORDERING INFORMATION ........................................................................................................ 10

4. UNPACKING .................................................................................................................................... 10

5. OCCUPATIONAL HEALTH & SAFETY / WORK HEALTH & SAFETY WARNINGS ...... 11

5.1 General Caution ................................................................................................................ 11 5.2 Earth Bonding ................................................................................................................... 11 5.3 High Temperatures ........................................................................................................... 11 5.4 High Voltage ...................................................................................................................... 12 5.5 Electro Static Discharge ................................................................................................... 12

6. INSTALLATION .............................................................................................................................. 13

7. OPERATION .................................................................................................................................... 14

7.1 Front and Rear Panel Functions (See Figure 2) ............................................................. 15 7.2 Front and Rear Panel Detail ............................................................................................ 15 7.3 User Adjustments ............................................................................................................. 16 7.4 Operation........................................................................................................................... 17

8. TECHNICAL DETAILS .................................................................................................................. 18

8.1 PA Metering Module ........................................................................................................ 18 8.2 Distribution PCB (Refer Figure 10) ................................................................................. 20 8.3 RF Driver Stage (Refer Figure 9) .................................................................................... 20 8.4 RF 100W PA PCB (Refer Figure 7 and Figure 8) ............................................................. 20 8.5 Seven Segment Display PCB (Refer Figure 11) .............................................................. 21

9. MAINTENANCE, INSPECTION AND REPAIR ADVICE ......................................................... 22

10. USER NOTES: ................................................................................................................................ 23



Notice The information contained in this document is subject to change without notice. RF Industries Pty. Ltd. makes no warranty of any kind with regard to this material, including but not limited to, the implied warranties of merchantability and fitness for a particular purpose. RF Industries Pty Ltd shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance or use of the material. All information contained in this manual has been reviewed. However RF Industries Pty Ltd accepts no liability for any omissions, errors or construed information.

2007-2015, RF Industries Pty Ltd. All rights reserved. Reproduction, adaptation or translation without prior written permission is prohibited except as allowed under copyright laws. For further information or help with this product contact your nearest RFI sales office or through the following;

Region USA EMEA ASIA PACIFIC

Sales email [email protected] [email protected] [email protected]

Tech Support [email protected] [email protected] [email protected]

Telephone Intl +1 (330) 486 0706 +44 (0) 1869 255772 +61 7 3621 9400

Telephone local 330 486 0706 01869 255772 1300 000 RFI

Fax Intl + 1 (330) 486 0705 +61 2 9630 0844

Web rfiamericas.com rfiemea.com rfi.com.au



PA88108 FM RF Power Amplifier

Front View

Rear View



1. General Description This manual contains the technical, installation and operating information for the PA88108 100W Linear RF Amplifier. The PA88108 is a full featured, high performance RF Power Amplifier for the FM frequency band.

1. The PA88108 Linear RF Amplifier is a solid state LDMOS RF power amplifier with an RF output of 100W in the VHF FM broadcasting band (87.5MHz to 108MHz). The unit is housed in a 19-inch rack mount case occupying 5RU space.

2. The PA88108 Linear RF Amplifier is completely “self-contained” with a built in PSU and cooling system

1.1 Structure

The amplifier comprises the following modules:

a) RF PA Module

b) PA Metering Module

c) RF Driver Module

d) Display Module

e) Distribution Module

1.2 Features

The PA88108 Linear RF Amplifier has standard features including the following:

a) Self-contained in a 5RU rack mounted unit

b) Remote telemetry with voltage free contacts and sample voltages.

c) Linear 4-stage, 5th generation “State of the Art” LDMOS design.

d) Built in cooling using three standard 120mm x 120mm A/C blowers.

e) 3 digit, 7 segment digital display.

f) ALC built in for absolute control of RF output power.

g) 48 SMPS unit (adjusted to +52V)

1.3 Block Diagram

Refer to the system block diagram in Figure 1 on the following page.



SamplerFWD/VSWR

RF Input(BNC)

RF Output(N-type)

RF Sample(BNC)

PowerSupply

MeteringAlarm Indication

Adjustment

Voltage/Current Sense Temp VSWRF/R

Temp

Power Adjust

Telemetry/ AlarmsConnector

(DB15)

Figure 1: System Block Diagram

1.4 Brief Description

a) RF Driver Module

The 50 Ohm RF input is fed via a 10dB attenuator; R1, R2 and R3 to the driver stage. The RF driver stage utilizes a 75 Ohm linear CATV amplifier (U4) with +34dB gain. A linear Mosfet amplifier stage (TR1) with +12dB gain is used to obtain the optimum output drive power. This is routed via a 4-way Wilkinson splitter to the power amplifier stages using suitable RG179/U coaxial cables.

b) Power Amplifier Module

The linear RF power amplifier utilizes a 4 stage LDMOS design. This design architecture provides redundancy, isolation and excellent linearity. The 4 stages are routed via a double section microstrip Wilkinson combiner which provides broad bandwidth and isolation between stages. A 7

th order low pass filter is provided to eliminate harmonics and a microstrip

coupler is also provided for monitoring and control purposes.

c) PA Metering Module

The power amplifier heatsink temperature is monitored via a thermistor on the RF heatsink assembly and is routed to the control stage to provide an alarm, protection and metering. RF forward and reflected signals are also routed to the control stage to provide alarms, protection and metering. Automatic Level Control (ALC) is provided on the control stage to provide a flat response on the RF power output with frequency using a pin attenuator circuit that monitors the power amplifier’s RF output. Telemetry functions via voltage free contacts and sample voltages are provided as standard.

d) Digital Display Module

The seven segment display provides a visual indication of all the metered parameters.

e) Metering and Distribution Module

This provides connection between the +52V/9.5Amp SMPS and the other modules. The module also provides “high-side” current monitoring for the four individual RF LDMOS stages in the linear power amplifier. Fuse holders with 3.15A fuses are also provided for each individual stage.



2. Specifications

Model Number PA88108

Frequency Band 87.5 – 108MHz

RF Output Power ≥ 100W Single Carrier (Adjustable via front panel)

RF Harmonic Suppression ≥ 60dB

RF Spurious Suppression ≥ 70dB

Intermodulation Products Typically -50dBc (w.r.t. individual carriers)

Bias Current per Output Device 0.85 Amps nominal

RF Gain +47dB nominal with adjustable gain

Gain Adjustment 5dB nominal via ALC

RF Input Return Loss ≥ 30dB

DC Current Consumption 7.5A @ 52V for 100W RF output into 50Ω

A/C Input Voltage 85V – 264V Full Range

A/C Frequency Variation 50 / 60Hz

A/C Input Power 400VA nominal

Storage Temperature -40°C to +60°C

Operating Temperature -10°C to +45°C

Relative Humidity 20% to 90% (non-condensing)

Operating Altitude ≤ 1500m above sea level

Cooling System Forced Air @ approx. 500m3/ hr

Physical Dimensions 480mm x 455mm / 225mm (5RU)

Acoustic Noise ≤ 50dBA

Weight Approx. 18.5kg

RF Fault Indication ≤ 80W (Red LED on front panel) (Adjustable)

Reflected Fault Indication ≥ 5W (Red LED on front panel) (Adjustable)

Reflected Fault Trip ≥ 8W (Red LED on front panel with 14 second recycle) (Adjustable)

Temperature Fault Indication ≥ 53°C (Red LED on front panel)

Table 1



3. Ordering Information

Ordering Information

RFI Part Number Description

PA88108 100W Linear RF Amplifier 87.5 – 108MHz

Table 2

4. Unpacking The PA881081 is packed heavy duty cardboard packaging. The User’s Manual is available for download from the RFI website. Although the packaging has been designed to provide suitable product protection during shipping, it is important to report any visible damage to the carrier immediately. It is the customers’ responsibility in the event of product damage, to lodge a damage claim with the carrier within a short period of time after receipt of the package. The time window for lodging the claim should be ascertained from the specific carrier as this may vary between carriers (typically 1 to 5 days). Please dispose of all packaging material responsibly.



5. Occupational Health & Safety / Work Health & Safety Warnings

5.1 General Caution

Only a suitably qualified person should be allowed to install and commission this equipment after comprehending and becoming familiar with all the safety and installation instructions contained in this User’s Manual. It will be assumed that a qualified person will have a fundamental knowledge of the objectives and use common sense where safety warnings are not necessarily explicit.

On unpacking the equipment, familiarise yourself with it and read and follow any and all warning labels. Please ensure that any warning labels are kept in a legible condition and replace if necessary.

Ensure all general, regional and site-specific installation and safety regulations are adhered to when working on high voltage installations, as well as regulations covering use of tools and personal protective equipment. It is the responsibility of the network operator or service provider to have in place and implemented a legally compliant Occupational Health and Safety (OHS) / Work Health and Safety (WHS) law as applicable, detailing prevention measures to avoid health hazards which may be associated with radiation from the antenna(s) connected to this equipment. Please ensure familiarisation and compliance to country specific regulations on RF exposure. Ensure all adjustable repeater settings comply with intended use and applicable National, State and Regional regulatory requirements. Please note that only the authorised licence holder for the respective frequencies or frequency range is allowed to operate this equipment. Ensure that access to this equipment is restricted to qualified personnel only. The unit weighs 18.5kg and is manageable for one person to lift. There is no On/Off switch on the unit – it becomes active as soon as AC or DC power is connected via the provided AC mains cable or DC power source. Do not allow the PA88108 or any associated equipment to become wet or to be subjected to a corrosive environment, humidity or temperatures outside the specified operating ranges. Do not operate the unit near any flammable substances or in a flammable atmosphere. Ensure that all RF termination connectors are fully mated and hand tightened. Use this equipment only for the purpose specified by RF Industries Pty Ltd. Do not carry out any modifications or attempt any repairs. The PA88108 is not intended to be field repairable and should be returned to RF Industries for service or repair.

5.2 Earth Bonding

An equipment earthing / grounding M5 threaded stud is provided at the rear of the enclosure located on the rear panel (refer Figure 2, #10) The FMC88108 must be adequately bonded to the common 19” rack earth/grounding connection point within the 19” rack frame/cabinet using the M5 stud provided.

5.3 High Temperatures

Owing to possible power dissipation within the equipment, the exposed rear portion of the equipment may reach relatively high temperatures. Please take the necessary precautions when servicing or removing the equipment.

Please allow adequate ventilation space around the unit when installing this equipment.



5.4 High Voltage

When operated from an AC power source this unit complies with the Australian AS/NZS 60950 equipment safety standard. There is no surge protection built into the PSU of the PA88108, so additional site specific lighting protection, voltage surge protection and earth bonding is recommended to reduce the risk of damage.

Regarding external antennas connected to the FMC88108-6, we recommend the use of adequate coaxial lighting protection and earth bonding through grounding kits on the RF feeder cables prior to termination into the respective RF termination connectors on the FMC88108-6. AC or DC mains should also be afforded surge protection.

5.5 Electro Static Discharge

Although exposure of the interconnect sockets / pins has been designed to significantly reduce the risk of electro static discharge (ESD), precautions must be observed during installation and maintenance to protect all the modules within the equipment.



6. Installation

The PA88108 is designed to be installed into standard 19” rack mount frames or cabinet spaces and is intended for indoor use only. Power connection to the unit must be made via the rear IEC connector with the required power capacity. The equipment must only be used with a properly earthed mains supply Cooling air for the unit is drawn from the front of the unit and is expelled at the rear. Adequate provisions must be made to ensure that the air flow is not impeded at either the front or the rear of the unit. Under no circumstances should the unit be allowed to become wet. Ensure that the power source is disconnected before removal of any covers. Installation summary: Lightning protection, grounding, and the appropriate torqueing of connectors and the sealing of terminations are all important facets of any system installation. Careful attention should be given to these areas The type of coaxial feeder cables that may be used with the PA88108 may vary, but generally their type will be determined by their length (and resulting insertion loss) and associated jumper/ tail requirements. Always follow engineering best practices for equipment installation.



7. Operation Note: It is recommended that the users familiarize themselves with the operating controls and connectors before using the equipment.

6

7

Figure 2: Front and Rear Panel Layout



7.1 Front and Rear Panel Functions (See Figure 2)

1. Three digit, seven segment LED display.

2. Function Select switch with LED indicators and scales.

3. RF power adjustment potentiometer.

4. Status and Alarm LED indicators for display of operating conditions.

5. Air intake for internal cooling system.

6. RF monitor output (BNC Female).

7. Air outlet for cooling system.

8. RF Input (BNC Female)

9. RF Output (N-type Female)

10. Chassis ground. A/C power input (IEC connector), provided for A/C mains input

11. 240V A/C power input (IEC connector).

12. A/C fuse holder: 38mm fuse rated at 6.3 Amp/240V

13. Telemetry connector: D-15 female connector for monitoring and control.

7.2 Front and Rear Panel Detail

a) Meter Display:

The meter indicates eight functions via yellow led indicators using a push button selector switch: 1. Forward power in “Watts”

2. Reflected power in “Watts”

3. Temperature in “°C”

4. PSU voltage in “Volts”

5. Mosfet #1 current in “Amps”




b) Status and Alarm indicators:

The status indicators provide indications for the following functions:

INDICATOR LED FUNCTION

PSU On GREEN +52V is active

Enabled GREEN RF output activated

AUX PSU GREEN Aux +15V PSU active

RF Fault RED RF power is ≤ 80W (Adjustable)

Reflected Fault RED Reflected power is ≥ 5W (Adjustable)

Temp Fault RED Temp is above 53°C

PSU Fault RED Power supply is faulty

Table 3

c) RF Monitor:

This BNC female provides an RF sample of the Transmitted output (-60dBc nominal).

d) RF Power adjust: This single turn potentiometer is provided to set the RF output power output via the ALC (Automatic level control), Pin

attenuator.



e) Rear panel telemetry connections: D15 female connector.

FUNCTION CONNECTOR PINS STATUS

RF Forward voltage Pins 2 and 1 (Ground) 1V dc for 100W

RF Reflected voltage Pins 3 and 1 (Ground) 1V dc for 10W

Temperature voltage Pins 4 and 1 (Ground) 2.5V dc for 25ºC

PSU Fault Pins 5 and 6 Voltage free contacts o/c for fault

RF disable Pin 8 and 9 (Ground) s/c to disable

Forward Fault Pins 10 and 11 Voltage free contacts o/c for fault

Reflected Fault Pins 12 and 13 Voltage free contacts o/c for fault

Temperature Fault Pins 14 and 15 Voltage free contacts o/c for fault

Ground Pins 1 and 9 Connected to chassis

NOTE: Alternative contact positions are available internally for the Telemetry outputs, (via Link selections on the PA

Metering module assembly).

SUMMARY ALARM: When a summary alarm is required the D15 Telemetry connector should be wired as follows. Summary contact is between pins 15 and 5. Connect pins (14 to 13), (12 to 11) and (10 to 6). When there are no faults the contact will be short circuit (s/c).

7.3 User Adjustments

User adjustments via top cover at front panel.

Read from left to right.

Test points (TP) are on Front Panel PCB (Z0186)

Potentiometer Function Comment

Pre-calibration only R73 Forward power cal. +5V / 100W @ TP6

Pre-calibration only R74 Reflected power cal. +3.54V / 5W @ TP7

Pre-calibration only R72 Reflected power trip Activates REFL Fault LED

Pre-calibration only R88 Reflected power fault Activates REFL Fault LED

User adjustable R85 RF fault Activates RF Fault LED

Pre-calibration only R109 Telemetry forward voltage +1V / 100W @ J11 pin 2

Pre-calibration only R110 Telemetry reflected voltage +0.5V / 5W @ J11 pin 3

Pre-calibration only R94 Temperature alarm @ 53ºC Activates Temp Fault Led

Pre-calibration only R60 Temperature cal. +5V / 25ºC @ TP5

Pre-calibration only R47 PSU fault cal. Activates PSU Fault Led

Pre-calibration only R10 Temperature meter cal. On Meter Display

Pre-calibration only R6 Reflected meter cal. On Meter Display

Pre-calibration only R2 Forward meter cal. On Meter Display

Pre-calibration only R16 PSU meter cal. On Meter Display

Note: The PA88108 amplifier is fully self- contained and it only requires an RF drive of between 0dBm and +3dBm nominal from a multi-channel source such as the FMC88108-6. The output power can be adjusted via the Power Adjust potentiometer on the front panel.

To test the RF Amplifier the following are required:

1. 250W RF Load/Attenuator.

2. VHF FM 6 Channel translator such as the FMC88108-6 with 6 x -4dBm carriers.



7.4 Operation

1. Connect the FMC88108-6 RF output (BNC) to the PA88108 RF input (BNC) on the rear panel using a 50 Ohm RG58 type

cable.

2. Connect 230V A/C mains to the IEC connectors on the amplifier and FMC88108 rear panels.

3. Connect the amplifier RF output (N Type) on the amplifier rear panel to the RF load / attenuator using a 50 Ohm RG214 type cable.

4. Adjust the RF power potentiometer on the front panel of the PA88108 fully anti clockwise (minimum).

5. Power on the PA88108 only and observe the front panel of the amplifier. Check the following.

a) PSU ON LED is illuminated.

b) ENABLED LED is illuminated.

c) AUX PSU LED is illuminated.

d) RF FAULT LED is illuminated.

e) REFL Fault LED is off.

f) TEMP Fault LED is off.

g) PSU Fault LED is off.

h) The three internal fans must be operating.

6. Observe Meter Display and ensure the following.

a) Forward power is 0W.

b) Reflected power is 0W.

c) Temperature reading is at room ambient.

d) Voltage reading is approximately +52 Volts.

e) Currents #1, #2, #3 and #4 are approximately 0.85Amps

7. Power on the FMC88108-6 Translator and adjust the RF output of the PA88108 amplifier to 100W on the Meter Display

(NB: This only applies if the FMC88108-6 is configured for 6 x -4dBm carriers) and check the following.

a) Ensure all Fault LEDs are OFF on the front panel.

b) Select REFL Power on front panel meter display and ensure this is below 1.5W (into the 50 Ohm load).

c) Select Currents on front panel digital meter and ensure they are approximately 1.75 Amps each.

d) Select Temperature on front panel digital meter after approximately 15 minutes and should read approximately 9°C above room ambient.

This completes the operation and test for the PA88108 and if other test equipment is available the RF spectrum should at least be

checked against the specification.



8. Technical Details NB: Some of the values described in the following paragraphs may not apply in a multi-carrier output application.

8.1 PA Metering Module

a) Power Supply

The +52V nominal DC input at J8 pins 1 and 4 is routed to a 1 Amp PCB fuse F1. LED indicator D40 (green) is provided after the fuse for PSU indication on the PCB. U12 (SMPS) provides a DC output of +28V nominal. LED D53 (ENABLED) indicates the supply is active. This PSU provides the 1 Amp supply to the RF PA driver section via J9, and has protections to disable it during

RF output reflected power and over temperature on heat-sink. U11 (SMPS) provides a DC output of +15V nominal and also a -27V “low current” output for the metering circuits. LED indicator D50 (AUX PSU) is provided for PSU active indication on the PCB.

b) Forward RF Detection

The forward RF sample is input at J5 (nominally +2dBm average) and is half wave rectified by diode D28 and DC averaged by R58, C24 and C25. This is required as the input has a 100% AM product due to the multiple

carriers. U8:A amplifies the DC level to a nominal +5V / 100W, adjusted via R73 (FWD CAL) at TP6. Temperature compensation is done via D30 in the feedback loop. The output from U8:A is monitored by U9:A and is compared to the voltage set by R85 (RF FAULT ALARM).

The output is routed to sheet 4 to provide a telemetry alarm.

c) Reflected RF Detection The reflected RF sample is input at J6 (nominally -2dBm average) and is half wave rectified by diode D29 and DC averaged by R59, C26 and C27. This is required as the input has a 100% AM product due to the multiple

carriers. U8:B amplifies the DC level to a nominal +5V / 10W, adjusted via R74 (REFL CAL) at TP7. Temperature compensation is done via D31 in the feedback loop. The output from U8:B is monitored by U9:B and is compared to the voltage set by R88 (VSWR ALARM CAL).

The output is routed to sheet 4 (figure 6) to provide a telemetry alarm. The output from U8:B is also monitored by U9:C and is compared to the voltage set by R72 (VSWR TRIP). The output is routed to timing circuit U9:D that provides a recycling delay of about 14 seconds. This is done to

disable the +28V PSU and switch off the RF driver during high reflected power situations.

d) Temperature Detection The temperature detection circuit operates using a thermistor which is connected to J7, pin 1 and 2. U7:A provides DC amplification and R60 provides calibration of the DC voltage. The DC voltage produced is calibrated to actual temp ÷10, (25°C gives 2.5V DC) via TP5. U7:A is monitored via U7:D and is compared to the voltage set by R94 to provide a temperature alarm around

53°C (TEMP ALARM). The output is routed to sheet 4 (figure 6) to provide a telemetry alarm. U7:A is also monitored via U7:C and is compared to the voltage set by R75 and R76 to provide a temperature

trip around 60°C (TEMP TRIP). This is done to disable the +28V PSU and switch off the RF driver during high temperature situations.

e) Metering Conversion Circuits

The forward (TP6) and reflected (TP7) voltages are routed and corrected via diodes D35, D37 (Forward) and D36 and D38 (Reflected) U10:B provides a linear 1V / 100W DC output for the forward voltage, adjustable via R109. U10:A provides a linear 1V / 100W DC output for the reflected voltage, adjustable via R110.

The diodes correct the no-linear power scale to a linear scale, enabling a linear scale meter to be used. These voltages are routed to the telemetry on sheet 4 (figure 6) and also the metering circuits on sheet 1



f) Metering Circuits A push button switch SW1 and circuit consisting of U2; U3 and U4 is used to select the required eight functions. The circuits are powered by a +5V regulator U8 and a -5V via D13 U2 is an up/ down counter and is configured to count to 8 and then restart at 1. U3 and U4 are selector switches with inputs allowing the 8-way switch function.

Functions:

Parameter LED Indicator Adjustment Scale

Forward Power D12 R2 Watts

Reflected Power D11 R6 Watts

Temperature D10 R10 °C

PSU Voltage D9 R16 Volts

Mosfet Current #1 D8 R11 Amps




Table 4

g) ALC Operation The AGC circuit operates around U1:A which operates as a differential integrator and amplifier that compares the output of U8:A (FWD VOLTAGE) to the DC voltage set by R20 (POWER ADJUST). The DC output is routed to the RF pin attenuator AT1. This allows the RF level at J3 (via the 10dB attenuator) to be controlled and attenuated via the setting on R20. The RF output at J2 is routed to the driver module.

The disable functions provided for reflected power, temperature and telemetry disable, reduce the RF output power by pulling down the voltage setting on R20 via diode D7.

h) PSU Fault Detection

The PSU voltage sample from the distribution module at J1, pin 5 is routed to U1:B (COMPARATOR) and a fault alarm is provided by the setting of R47 (PSU FAULT ADJUST). This allows relay K1:C to operate when the sampled voltage is low. PSU fault LED D26 is illuminated via K1: A contact when the fault occurs. LED D27 provides an indication that the power supply is ON. A relay contact from K1:B is routed to sheet 4 (figure 6, pg. 23) to provide a telemetry alarm.

i) Telemetry Circuits The fault alarms are routed to transistors T1, T2 and T3, which activates the relays K2:C; K3:C and K4:C and

provides the contacts on the telemetry connector J11. The telemetry functions are shown below:

Function Connector Pins Status

RF Forward Voltage Pins 2 and 1 (Ground) 1V DC for 100W

RF Reflected Voltage Pins 3 and 1 (Ground) 1V DC for 10W

Temperature Voltage Pins 4 and 1 (Ground) 2.5V DC for 25°C

PSU Fault Pins 5 and 6 Voltage free contacts

RF Disable Pins 8 and 9 (Ground) S/C to disable

Forward Fault Pins 10 and 11 Voltage free contacts (O/C for fault)

Reflected Fault Pins 12 and 13 Voltage free contacts (O/C for fault)



8.2 Distribution PCB

This provides connection between the +52V/9.5A SMPS and other modules. The module provides ‘high-side’ current monitoring via IC1 to IC4 using resistors R1 to R4 to sample the current flow. The four samples DC outputs proportional to the current flow are routed to the SK7 pin1 to pin 4. Fuse holders F1 to F4 with 3.15A fuses are also provided for each stage. A combined sample voltage of the four fused outputs is routed via R6 to R9 inclusive, to SK7 pin 5. This voltage is used for fault

monitoring.

8.3 RF Driver Stage

The RF driver consists of a -10dB input attenuator that is routed to a +34dB gain CATV linear amplifier. This provides excellent return loss. The output of the linear amplifier is routed to ferrite transformer T1 (3:1 ratio) and then to a 1W, +12dB gain linear RF Mosfet amplifier, T1. The bias current is set via R11. The total current is set to 0.85A nominal. The amplifier section is powered from a +28V DC external supply via SK1.

The output of the 1W amplifier is routed to a single section coaxial Wilkinson splitter that provides four equal RF outputs. This transforms the impedance from 25 Ohms at TR1 to 50 Ohms at each output.

8.4 RF 100W PA PCB

Note: The circuitry for the four ‘push-pull’ amplifier stages are identical and only one stage needs to be described.

a) DC Voltage input. The +52V nominal DC input is routed via an RF filter, C11, C12, C10, C13, C101, C5, C6, C7 and L2, to isolate

any RF frequencies from entering or leaving the power amplifier stage.

b) RF Input / Output Stage Circuits The RF inputs are routed to the four RF amplifier input stages via C2 and T1 (2:1 ferrite transformer). A 100 Ohm

balance load is provided between each pair of stages to ensure maximum isolation between stages. The RF amplifier section consists of four ‘Class AB’ biased, 25W, LDMOS RF ‘push-pull’ stages with coaxial wideband transformers T2.

The RF signal from each stage is then routed via a 50 Ohm coaxial balun to matching inductor L3. Bias adjustment is provided via R7 which is used to set the bias current for the RF Mosfet (typically 0.85 Amps

per stage) in order to set it in ‘Class AB’ mode with minimum intermodulation products (typically -50dBc with 6 x 16W FM carriers) The four stages provide 100W output with a gain of approximately 21dB and amplitude response of ± 0.5dB between 87.5MHz and 108MHz

c) RF Combiner Section.

The combiner section consists of a wideband, microstrip, 4-way Wilkinson (double section with three 100 Ohm balance loads (provided for maximum isolation between stages) This provides excellent redundancy and a very good 50 Ohm match

d) RF Harmonic Filter and Coupler.

The 7th

order RF harmonic filter consists of three inductors and four capacitors. The filter output is routed via a 50 Ohm micro-stripline to the RF coupler section to provide forward, reflected and monitoring RF samples for use in the control PCB. The capacitors connected to ground at the outputs of the coupler lines are used to correct the +6dB / octave slope of the coupling lines, thus providing a flat frequency response. The RF monitor coupler uses an inductor as it also reduces the common mode pickup between grounds. This section is provided with a screening can.



8.5 Seven Segment Display PCB

The display consists of the three seven segment LED (single digit) displays. These are driven via IC3 which is a complete digital volumeter chip that provides the functions of A/D conversion and logic control. An adjustment for the sensitivity is provided via R3. The sensitivity is approximately 200mV. The decimal points for the seven segment displays are link selectable locally via LK1-LK4 and remotely Via SK1. An on-board +5V regulator, IC1 and a +5V to -5V inverter, IC2 are provided.



9. Maintenance, Inspection and Repair Advice

No special maintenance program is required for the PA88108, but a regular Periodic Maintenance Inspection (PMI) checking all N Male termination connectors on the RF coaxial connectors on the PA88108 is recommended. All other DB15 and/or Phoenix connectors must be firmly located and pushed into their corresponding mating sockets, with fastening screws tightened securely. The PA88108 is not considered field repairable. Should it be considered that any unit may be faulty through diagnosis, it should be replaced or returned to RFI for repair.

Contact Information

If you would like more information on the PA88108 product and its applications, please contact your nearest RFI Sales Office.

For more information on RFI products, please visit us at http://www.rfiwireless.com.au/

http://www.rfiwireless.com.au/



10. User Notes:

PA88108 Series User’s Manual


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