G4WIM PA controller

An advanced PA controller design by Tim G4WIM and described in CQ-TV 265 - PCB's will be available from the BATC shop.

Introduction

This project came about as a result of needing to remote control and monitor a 2.4GHz power amplifier for the QO-100 satellite up link. In the case of G4WIM the amplifier is at the end of 75 metres of cable directly beneath the feed point of a 1.2 metre dish. So running from the shack to the PA was not an option!

It has evolved from a simple controller which relied on either 5 or 12 Volts being sent up the coax to set off, standby or transmit modes into a multi-purpose design.

Configurations

The resulting system can be configured in three ways:

• Full remote control of the PA and shack monitoring of vital signs – using radio link.
• When PA is in the shack, local control and monitoring - no radio link.
• Remote control of PA by means of DC down the coax – no radio link or remote monitoring

The most likely use cases are 1 and 2. In this article I refer to the PA with associated control and telemetry hardware as the MASTER and the remote display / control in the shack as the SLAVE. When used as #2 above there is no SLAVE and the MASTER serves as control and display.

Monitoring

In all cases it allows monitoring of the following analogue signals:

• Vdd, 100mV resolution
• Idd, 100mA resolution
• PA temperature, 0.1C resolution
• Bias voltage, 10mV resolution for LDMOS, 1V for Pyro Jo
• RF power (forward or reverse but not both – depends on HW implementation)
• Fan status on or off
• Standby status on or off

Amplifier choices

The design was initially conceived for a Pyro Jo PA which needs 24V DC bias to activate it, subsequently it was modified to provide a temperature compensated bias for LDMOS FET’s. Basically for the LDMOS FET use the temp compensated bias circuit and for the Pyro JO PA use the 24V DC device – one or the other NOT both. See schematics for more detail.

• Link 3 jumper when installed configures the firmware for Pyro Jo PA and when not installed configures for LDMOS operation.
• Link 4 jumper when installed configures the firmware for SLAVE operation and when not installed configures for MASTER operation.

MOST IMPORTANT, links 3 & 4 only configure the firmware, additionally if you are using LDMOS FET PA DO NOT install or use the 24V DC power module as it will instantly destroy the FET.

Hardware

The design uses the same PCB in all cases but populated slightly differently for each of the three use cases above. The BoM and schematics indicate what needs to be fitted for each use case.

400px

For each use case firmware works differently and is jumper selected as mentioned above.

Note, if RF power is not being monitored then the RF power sensor input on pin 1 of J3 must be connected to ground to disable the function. Normally RF power will only be shown when on transmit and above a certain threshold.

Documentation

Bill of material

Schematics

• File:PA CONTROL WIRING SHACK DISPLAY.pdf

• File:PA CONTROL WIRING SHACK DISPLAY.pdf

• File:PA CONTROL WIRING PJ SHACK.pdf

• File:PA CONTROL WIRING LDMOS THERMISTOR.pdf

• File:PA CONTROL WIRING PJ MAST.pdf

• File:PA CONTROL WIRING LDMOS SHACK.pdf

• File:PA CONTROL WIRING LDMOS MAST.pdf

Source code

File:Atmel_BATC_Unified_PA_Controller.zip

The radio link uses an nRF905 and Atmel nano – this solution is a copy of this design http://blog.zakkemble.net/nrf905-avrarduino-librarydriver/comment-page-1/ but with minor code changes. It is very easy to build / modify using the Arduino environment. The only minor code change required is to remove the “TO” time out message being sent. If this line is not commented the atmega 328 thinks the link is still good as it’s getting traffic.

Comment out line 110 as per below:

if(timeout) // Timed out{Serial.println(F("TO"));break;}

Wireless Serial Link Arduino code is found here: https://github.com/zkemble/nRF905/tree/master/arduino/nRF905/examples/wirelessSerialLink