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HF PA kit with Ultimate3S transmitter kit
1. Introduction
The QRP Labs HF PA kit has an 8-bit shift register (74HC595) whose outputs control an 8-bit Digital-
to-Analogue converter (DAC). This DAC controls a discrete-component power modulator with
foldback current limiting. A microcontroller can load a sequence of values into the shift register in
such a way that a raised cosine shape is applied to the RF envelope.
This application note explains how to interface the PA kit to the QRP Labs Ultimate3S transmitter kit.
The assembly document for the PA kit is ESSENTIAL reading, prior to this application note!
2. Block Diagram
The basic Ultimate3S transmitter is shown in the top half of this diagram. The Low Pass Filter (the
LPF) is drawn as a separate block to the Ultimate3S transmitter. In reality the LPF is a plug-in module
on the Ultimate3S PCB. If you are running a multi-band Ultimate3S then there is a LPF plugged into
your Ultimate3S PCB, and a 5-band Relay-switched extension PCB bolted behind that. As far as the
5W HF PA kit is concerned, the principles are the same in the single-band and multi-band cases.
Rev 1.01
AN004
1
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Summary of Contents for QRP Labs HF PA kit Series
- Page 1 HF PA kit with Ultimate3S transmitter kit 1. Introduction The QRP Labs HF PA kit has an 8-bit shift register (74HC595) whose outputs control an 8-bit Digital- to-Analogue converter (DAC). This DAC controls a discrete-component power modulator with foldback current limiting. A microcontroller can load a sequence of values into the shift register in such a way that a raised cosine shape is applied to the RF envelope.
- Page 2 5W HF PA kit at the BACK of the stack, due to the 65mm tall heatsink. You will also need to purchase a set of four 25mm nylon spacers from the QRP Labs shop, spare parts section. The physical module assembly is shown in the diagrams below, for the single band system (below left) and multi-band (below right).
- Page 3 The easiest place to take RF from the Ultimate3S is at the Q2 or Q3 transistors. The best way to cut the RF circuit between the original Ultimate3S PA and the Low Pass Filter on the U3S PCB, is to remove capacitor C5.
- Page 4 Multi-band Ultimate3S with 5W HF PA kit and relay-switched LPF kit Rev 1.01...
- Page 5 This diagram section (right) shows detail of how to connect the 200mW RF from the Ultimate3S PCB “Q3” pad, to the 5W HF PA PCB. Remember that you will be using only a single BS170 in the U3S, so there will be no transistor installed at Q3. When connecting the RF output of the 5W HF PA back to the filter input on the Ultimate3S, it is convenient to use the...
- Page 6 5. Ultimate3S configuration This section applies if you are using the full 5W HF PA kit assembly, including the raised cosine envelope shaping. The Ultimate3S requires at least firmware version v3.12. There is a configuration screen as follows: Shaping {ms Max} 05 115 The first parameter is the rise/fall time of the raised cosine envelope that will be generated.
- Page 7 6. References For updates relating to the PA kit please visit the QRP Labs PA Kit page http://qrp-labs.com/pa Refer to the PA Assembly instructions, download at the PA Kit page http://qrp-labs.com/pa For any questions regarding the assembly and operation of this kit please join the QRP Labs group, see http://qrp-labs.com/group for details...