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QRP Labs QCX+ Assembly Instructions Manual

Single band, high performance 5w cw transceiver with built-in alignment and test equipment, iambic keyer, wspr beacon mode, and more
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QCX+ CW Transceiver
QCX+ 5W CW Transceiver kit assembly instructions
PCB Rev 4
The "QCX+": a single band, high performance 5W CW
Transceiver with built-in alignment and test equipment,
iambic keyer, WSPR beacon mode, and more...
Designed and produced by QRP Labs, 2017-2020
pictured with:
Heil Sound Pro Set 3 headphones
https://heilsound.com/products/pro-set-3/
and
Palm Radio pico paddle
http://palm-radio.de
1
QCX+ assembly Rev 1.11

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Summary of Contents for QRP Labs QCX+

  • Page 1 PCB Rev 4 The “QCX+”: a single band, high performance 5W CW Transceiver with built-in alignment and test equipment, iambic keyer, WSPR beacon mode, and more... Designed and produced by QRP Labs, 2017-2020 pictured with: Heil Sound Pro Set 3 headphones https://heilsound.com/products/pro-set-3/ Palm Radio pico paddle http://palm-radio.de...

  • Page 2: Table Of Contents

    Contents 1. Introduction.................................5 2. Parts list..................................6 3. Assembly – general guidelines...........................11 3.1 Inventory parts..............................17 3.2 Wind and install transformer T1..........................18 3.3 Install IC2 socket..............................24 3.4 Install DIP integrated circuits IC3, IC5-10......................25 3.5 Install all 100nF (0.1uF, “104”) capacitors......................26 3.6 Install all 470nF, “474” capacitors........................27 3.7 Install all 1nF, “102”...
  • Page 3 3.47 Install power connector.............................68 3.48 Install 7805 voltage regulator IC11........................69 3.49 Wind and install toroid L4..........................70 3.50 Wind and install toroid L2..........................72 3.51 Wind and install toroids L1 and L3........................73 3.52 Install RF output BNC connector........................74 3.53 Install 3.5mm stereo jack connectors........................75 3.54 Install header pin connectors JP3, JP4 and JP5....................76 3.55 Install nylon header spacers if required......................77 3.56 Install Front panel PCB resistors R44 and R65....................79...
  • Page 4 6. Fault-finding................................124 6.1 Blank LCD or blocked LCD..........................124 6.2 No backlight at all..............................124 6.3 A row of blocks appears on the top row......................124 6.4 DC voltage readings............................125 6.5 RF Power output check............................127 7. Measurements................................129 7.1 Equipment.................................129 7.2 Transceiver current consumption........................129 7.3 Transmitter power output..........................130 7.4 Class-E Power Amplifier drain waveform......................131 7.5 RF envelope key-shaping...........................131...

  • Page 5: Introduction

    Thank you for purchasing this high performance single-band 5W CW transceiver kit, the QCX+ (for QRP Labs CW Xcvr +). This kit has a long list of features! Easy to build, two-board design, spacious 10 x 13cm main board with main circuit and ...

  • Page 6: Parts List

    Please make use of troubleshooting resources at if you have any http://qrp-labs.com/qc xp problems. If you need further help, join the QRP Labs discussion forum on groups.io and post a message about your problem. 2. Parts list Resistors (all fixed resistors are ¼-Watt, 1% tolerance)
  • Page 7 Value Description Component numbers 2.2uF Label “225” 10uF Electrolytic C37, 38, 51 470uF Electrolytic C24, 47 30pF Ceramic trimmer capacitor Band-specific capacitors (50V, 5% capacitors which must be C0G/NP0 type) Note: depending on band, some capacitors may be left over at the end. This is normal! 160m Value Description...
  • Page 8 30m (no C8 capacitor) Value Description Component numbers 22pF Label “220” 30pF Label “300” 270pF Label “271" C27, 28 560pF Label “561” C25, 26 20m (no C5 or C8 capacitors) Value Description Component numbers 30pF Label “300” 180pF Label “181" C27, 28 390pF Label “391”...
  • Page 9 Band-specific inductors 160m Value Description Component numbers 4.0uH 31 turns on T37-2 core (red) 6.4uH 40 turns on T37-2 core (red) 3.9uH 30 turns on T37-2 core (red) 1.4uH 19 turns on T37-2 core (red) 3+3+3+10 turns, FT50-43 (black) Value Description Component numbers 2.4uH...
  • Page 10 Value Description Component numbers 0.77uH 16 turns on T37-6 core (yellow) L1, L3 0.90uH 17 turns on T37-6 core (yellow) 0.40uH 10 turns on T37-2 core (red) 3+3+3+30 turns, T50-2 core (red) Value Description Component numbers 0.55uH 13 turns on T37-6 core (yellow) L1, L3 0.67uH 15 turns on T37-6 core (yellow) 0.32uH 9 turns on T37-2 core (red)

  • Page 11: Assembly - General Guidelines

    I recommend just install everything then power up. As per standard QRP Labs practice, the ATmega328P microcontroller has a 28-pin DIP socket in case you may wish to subsequently replace it for firmware upgrades etc. The Si5351A and FST3253 ICs are only available in surface mount packages so these are already soldered to the PCB for you, at the factory.
  • Page 12 You may find it convenient to inventory the resistors and capacitors and sort them by value, so that you can easily find the correct ones as you work through the assembly steps. Use of a good quality soldering iron and solder is highly recommended for best results! The following diagrams show the PCB layout and track diagrams of the front panel and main PCBs of the QCX+ kit.
  • Page 13 QCX+ assembly Rev 1.11...
  • Page 14 QCX+ assembly Rev 1.11...
  • Page 15 Tracks shown in BLUE are on the bottom layer. Tracks shown in RED are on the top layer. There are only two layers (nothing is hidden in the middle). Not shown in this diagram are the extensive ground-planes, on both sides of the board. Practically everything on both layers that isn’t a RED or BLUE track, is ground-plane! The two ground-planes are connected at frequent intervals (not more than 0.1-inches) by vias.
  • Page 16 Main board: Front panel board: QCX+ assembly Rev 1.11...

  • Page 17: Inventory Parts

    Inventory parts Refer to parts list in section 2. The following photographs are to aid component identification. The resistors and capacitors are omitted. Si5351A and FST3253 are already soldered to the board. QCX+ assembly Rev 1.11...

  • Page 18: Wind And Install Transformer T1

    Wind and install transformer T1 This is the only really tricky piece of the assembly: the receiver input transformer T1. Follow these instructions carefully, it is tricky but quite feasible if you go step by step. Note that this installation used to be done later in the manual.
  • Page 19 QCX+ assembly Rev 1.11...
  • Page 20 The number of turns in each winding depends on the band you are building the kit for. Refer to the following table. For convenience, the remainder of the instructions in this section refer to the 40m version (38 + 5 + 5 + 5 turns). But MAKE SURE you wind the correct number of turns and toroid for your band! Band Toroid...
  • Page 21 There is a suggested modified way of winding the turns for 60/80m versions, which may make it easier; see http://www.qrp-labs.com/qcx/qcxmods.html#80m In all cases, there is one long secondary winding, and three other short identical windings. To make things easier, we will wind all windings together in one go, this will guarantee that the “sense”...
  • Page 22 five more and make a loop on the fifth. Then finally five more turns to complete the toroid’s 53 windings. Count the windings to make sure you have 53. When you are sure everything is fine, cut the wire leaving about 3cm of wire free at the end. Thread the original start of your winding (from step 1) into hole 2 in the diagram.
  • Page 23 hole 8. So now you have the “primary” winding consisting of five turns, between holes 3 and 4. Twist the two new wires under the board again, to keep everything in place. Finally, cut and un-twist the loop which you created first, which was between the 38 turns of the toroid winding.

  • Page 24: Install Ic2 Socket

    Install IC2 socket Install the 28-pin IC socket for IC2. Take care to match the dimple on the socket, with the dimple on the PCB silkscreen. It is critical to insert the microcontroller with the correct orientation. Lining up the dimple on the PCB silkscreen, socket and actual IC is the best way to avoid confusion and potential error.

  • Page 25: Install Dip Integrated Circuits Ic3, Ic5-10

    Install DIP integrated circuits IC3, IC5-10 In the same way, install the Dual-Inline-Package integrated circuits IC3 and IC5-10. We install these now because they have more pins than all the passive components (resistors, capacitors etc) and it is easiest to reach and install the ICs properly when they are alone on the board. IC3 is the only 14-pin DIP chip.

  • Page 26: Install All 100Nf (0.1Uf, "104") Capacitors

    Install all 100nF (0.1uF, “104”) capacitors There are 16 100nF (0.1uF) capacitors, these have the code “104” written on them. Be sure to identify the correct capacitors, using a magnifying glass or jeweller’s loupe. These capacitors are C2, C3, C6, C12, C29, C32, C34, C35, C36, C39, C40, C41, C48, C49, C50 and C52. Place each in the correct position on the board, and slightly bend the legs outwards at about 30-degrees angle so that they stay in place.

  • Page 27: Install All 470Nf, "474" Capacitors

    Install all 470nF, “474” capacitors The 470nF capacitors are labelled “474”, and are capacitors C11, C43, C44, C45 and C46. QCX+ assembly Rev 1.11...

  • Page 28: Install All 1Nf, "102" Capacitors

    Install all 1nF, “102” capacitors The 1nF capacitors are labelled “102” and are capacitors C14, C16, C18, C23 and C33. QCX+ assembly Rev 1.11...

  • Page 29: Install All 10Nf, "103" Capacitors

    Install all 10nF, “103” capacitors The 10nF capacitors are labelled “103” and are capacitors C4, C7, C10 and C42. QCX+ assembly Rev 1.11...

  • Page 30: Install 47Nf, "473" Capacitors

    Install 47nF, “473” capacitors The 47nF capacitors are labelled “473” and are capacitors C9 and C13. QCX+ assembly Rev 1.11...

  • Page 31: Install 39Nf, "393" Capacitor

    3.10 Install 39nF, “393” capacitor The 39nF capacitor is labelled “393” and is C17. QCX+ assembly Rev 1.11...

  • Page 32: Install 2.2Nf, "222" Capacitors

    3.11 Install 2.2nF, “222” capacitors The 2.2nF capacitors are labelled “222” and are C19 and C20. QCX+ assembly Rev 1.11...

  • Page 33: Install 33Nf, "333" And 3.3Nf, "332" Capacitors

    3.12 Install 33nF, “333” and 3.3nF, “332” capacitors These are labelled “333” and “332”, and in parallel make up 36nF. They are C15 and C53. QCX+ assembly Rev 1.11...

  • Page 34: Install Capacitors C25 And C26 From The Low Pass Filter Kit

    3.13 Install capacitors C25 and C26 from the Low Pass Filter kit The value of these capacitors depends on your chosen band. The capacitors are located inside the separate Low Pass Filter bag in your main kit bag. Refer to the following table to find the correct capacitor value for your band: Band Value...

  • Page 35: Install Capacitors C27 And C28 From The Low Pass Filter Kit

    3.14 Install capacitors C27 and C28 from the Low Pass Filter kit The value of these capacitors depends on your chosen band. The capacitors are located inside the separate Low Pass Filter bag in your main kit bag. Refer to the following table to find the correct capacitor value for your band: Band Value...

  • Page 36: Install Capacitor C30

    3.15 Install capacitor C30 This capacitor is band dependent. The kit contains all required capacitor values for all bands. Install the one appropriate to your band. Refer to the following table to find the correct capacitor value for your band: Band Value Label...

  • Page 37: Install Capacitors C5 And C8

    3.16 Install capacitors C5 and C8 These capacitors are band dependent. They add parallel capacitance to trimmer capacitor C1 to bring it to the required value. The kit contains all required capacitor values. Install the capacitor(s) appropriate to your band. Refer to the following table to find the correct capacitor value(s) for your band.

  • Page 38: Install 1Uf, "105" Capacitors C21, And C22

    3.17 Install 1uF, “105” capacitors C21, and C22 There are two 1uF capacitors labelled “105”, which are C21 and C22. QCX+ assembly Rev 1.11...

  • Page 39: Install 2.2Uf, "225" Capacitor C31

    3.18 Install 2.2uF, “225” capacitor C31 The capacitor has 5.08mm pin spacing, but the holes are 2.54mm – you need to bend the wires carefully to fit in the holes. QCX+ assembly Rev 1.11...

  • Page 40: Install 1N4148 Diodes

    3.19 Install 1N4148 diodes There are 5 small glass red-ish coloured diodes, D1, D2, D4, D5 and D6, which are all installed flat on the PCB. In all cases it is critical to install the diodes the right way around, these are a polarised component and must only be installed in the PCB with the correct orientation! The PCB silkscreen printing shows a white stripe at the end of the diode body which must match the black stripe on the left end of the diode.

  • Page 41: Install 1N5819 Diode

    3.20 Install 1N5819 diode This diode D3 is the larger diode with a black body, and a white stripe. It is installed horizontally. Again, it must be orientated correctly, with the white stripe on the diode matching the white stripe on the PCB.

  • Page 42: Install 20Mhz Crystal Xtal1

    3.21 Install 20MHz crystal XTAL1 The engraving on this crystal is “20.000”. QCX+ assembly Rev 1.11...

  • Page 43: Install 27Mhz Crystal Xtal2

    3.22 Install 27MHz crystal XTAL2 All other bands: 27MHz crystal, engraved “27.000” Note that if you are going to install the TCXO module option, DO NOT install 27MHz XTAL2. Skip this step! If using the TCXO module, menu 8.5 must be manually changed to 25,000,000. QCX+ assembly Rev 1.11...

  • Page 44: Install All Main Pcb 10K Resistors

    3.23 Install all main PCB 10K resistors There are 15 10K resistors to be installed on the main board of the kit, these are R1, R2, R7, R10, R14, R21, R34, R36, R39, R40, R51, R52, R57, R58 and R64. The colour code is brown-black- black-red-brown.

  • Page 45: Install All Main Pcb 1K Resistors

    3.24 Install all main PCB 1K resistors There are 10 1K resistors to be installed on the main board of the kit, these are R3, R4, R19, R26, R37, R49, R54, R55, R62 and R63. The colour code is brown-black-black-brown-brown. There will be one 1K resistor left over at the end, this is to be installed on the front PCB in a later construction step (it is R45).

  • Page 46: Install All Main Pcb 3.3K Resistors

    3.25 Install all main PCB 3.3K resistors There are 11 3.3K resistors to be installed on the main board of the kit, these are R12, R13, R15, R16, R20, R22, R23, R25, R53, R56, and R59. The colour code is orange-orange-black-brown- brown.

  • Page 47: Install All 100-Ohm Resistors

    3.26 Install all 100-ohm resistors There are four 100-ohm resistors in the kit, these are R5, R6, R8 and R9. The colour code is brown-black-black-black-brown. QCX+ assembly Rev 1.11...

  • Page 48: Install 120K Resistors

    3.27 Install 120K resistors There are three 120K resistors in the kit, these are R38, R43 and R60. The colour code is brown- red-black-orange-brown. QCX+ assembly Rev 1.11...

  • Page 49: Install 33K Resistors

    3.28 Install 33K resistors There are two 33K resistors in the kit, these are R28 and R29. The colour code is orange-orange- black-red-brown. QCX+ assembly Rev 1.11...

  • Page 50: Install 47K Resistors

    3.29 Install 47K resistors There are two 47K resistors in the kit, these are R30 and R31. The colour code is yellow-purple- black-red-brown. QCX+ assembly Rev 1.11...

  • Page 51: Install 36K Resistors

    3.30 Install 36K resistors There are two 36K resistors in the kit, these are R32 and R33. The colour code is orange-blue- black-red-brown. QCX+ assembly Rev 1.11...

  • Page 52: Install The Main Pcb 270-Ohm Resistor

    3.31 Install the main PCB 270-ohm resistor There is one 270-ohm resistor to be installed on the main board of the kit, this is R50. The colour code is red-purple-black-black-brown. Note that this resistor is larger than the other resistors. This is because higher heat dissipation is required for R48 which is also 270-ohms and is used on the front PCB.

  • Page 53: Install 1.2K Resistor R42

    3.32 Install 1.2K or 820-ohm resistor R42 A 1.2K resistor has colour code brown-red-black-brown-brown. An 820-ohm resistor has colour code grey-red-black-black-brown. Kits produced from July 2022 onward are supplied with an 820-ohm resistor. Before this date, the resistor was 1.2K. The change was necessary due to slightly different characteristics of the new batch of Q6 transistor (MPS751).

  • Page 54: Install 150-Ohm Resistor R41

    3.33 Install 150-ohm resistor R41 This resistor has colour code brown-green-black-black-brown. QCX+ assembly Rev 1.11...

  • Page 55: Install 3.9K Resistor R61

    3.34 Install 3.9K resistor R61 This resistor has colour code orange-white-black-brown-brown. QCX+ assembly Rev 1.11...

  • Page 56: Install 4.3K Resistor R18

    3.35 Install 4.3K resistor R18 This resistor has colour code yellow-orange-black-brown-brown. QCX+ assembly Rev 1.11...

  • Page 57: Install 5.1K Resistor R11

    3.36 Install 5.1K resistor R11 This resistor has colour code green-brown-black-brown-brown. QCX+ assembly Rev 1.11...

  • Page 58: Install 750K Resistor R35

    3.37 Install 750K resistor R35 This resistor has colour code purple-green-black-orange-brown. QCX+ assembly Rev 1.11...

  • Page 59: Install 500-Ohm Multi-Turn Trimmer Potentiometer

    3.38 Install 500-ohm multi-turn trimmer potentiometer This resistor is the small blue box component with label “501”. It is R27. The screw on the resistor should match the screw on the PCB silkscreen and layout diagram. But it is not a big problem if it does not;...

  • Page 60: Install 50K Multi-Turn Trimmer Potentiometers

    3.39 Install 50K multi-turn trimmer potentiometers There are two 50K multi-turn trimmer potentiometers, R17 and R24. They are the small blue box components with label “’503”. The screws on the resistors should match the screws on the PCB silkscreen and layout diagram. But it is not a big problem if they does not; everything will still work fine.

  • Page 61: Install Two 47Uh Inductors

    3.40 Install two 47uH inductors There are two 47uH inductors, L5 and L6. These look like short fat resistors. They are installed horizontally on the PCB. QCX+ assembly Rev 1.11...

  • Page 62: Install 10Uf Capacitors

    3.41 Install 10uF capacitors There are three 10uF capacitors in the kit: C37, C38 and C51. These are polarised electrolytic capacitors and MUST be installed with the correct orientation! The capacitor NEGATIVE wire must be installed in the hole indicated on the PCB silkscreen and the layout diagram by the solid black bar;...

  • Page 63: Install 470Uf Capacitors

    3.42 Install 470uF capacitors These two capacitors are also polarised electrolytics and must be orientated correctly (see former section). QCX+ assembly Rev 1.11...

  • Page 64: Install 30Pf Trimmer Capacitor C1

    3.43 Install 30pF trimmer capacitor C1 Insert the component pins carefully and with the correct orientation which matches the PCB. Cut the small pin stubs on the underside (solder side) of the PCB, they only protude a few mm but when installed in the enclosure could be rather close to the aluminium floor.

  • Page 65: Install Mps751 Transistor Q6

    3.44 Install MPS751 transistor Q6 Be careful to correctly identify this transistor by its markings, as the package style is similar to the other transistors. Carefully bend and insert the wires so that the transistor’s flat side is flat flush against the PCB surface, and the body of the transistor is aligned with the square on the layout diagram (which is not...

  • Page 66: Install All Bs170 Transistors

    3.45 Install all BS170 transistors The remaining transistors in the kit are BS170 MOSFETs and there are six of them: Q1, Q2, Q3, Q4, Q5 and Q7. For Q1, Q2 and Q3, carefully follow the same installation procedure as the previous section, making sure that the transistors are neatly aligned in the correct positions near the hole in the PCB.

  • Page 67: Install 2X3-Pin In-Circuit Programming Header

    3.46 Install 2x3-pin in-circuit programming header This male pin header can be used to connect an AVR Programmer to apply firmware updates if desired. This is NOT the 2x3-pin female header connector socket which is later installed on the front panel display board.

  • Page 68: Install Power Connector

    3.47 Install power connector Install the 2.1mm power connector, orientated to match the PCB silkscreen. It is important to install this accurately so that if you install the QCX+ in the aluminium enclosure, the connector is correctly aligned with the rear panel holes. QCX+ assembly Rev 1.11...

  • Page 69: Install 7805 Voltage Regulator Ic11

    3.48 Install 7805 voltage regulator IC11 Install the 7805 voltage regulator, orientating it so that the metal tab is facing outwards from the PCB, along the edge of the PCB. Push the pins all the way down into the holes until the thicker part of the pins reaches the PCB surface.

  • Page 70: Wind And Install Toroid L4

    This is the number 1 cause of problems with QRP Labs kit construction: failure to remove the wire enamel. One method of removing the wire enamel is to scrape it off at the ends, either with sandpaper, or carefully scratching with a knife or wire cutters.
  • Page 71 QCX+ assembly Rev 1.11...

  • Page 72: Wind And Install Toroid L2

    3.50 Wind and install toroid L2 L2 is a small toroid ring painted yellow or red on one side. It is part of the supplied Low Pass Filter kit bag. Again, keep the wire tight and evenly spaced around the toroid. Installation of the inductor is similar to the previous section.

  • Page 73: Wind And Install Toroids L1 And L3

    3.51 Wind and install toroids L1 and L3 L1 and L3 are small toroid rings painted yellow or red on one side. They are part of the supplied Low Pass Filter kit bag. Again, keep the wire tight and evenly spaced around the toroid. Installation of the inductor is similar to the previous section.

  • Page 74: Install Rf Output Bnc Connector

    The connector has RF and Ground connections, and two fat rods which are for mechanical stability only. Accurate alignment is very important, to ensure that the connector fits into the hole of the optional QRP Labs QCX+ enclosure (if used). QCX+ assembly Rev 1.11...

  • Page 75: Install 3.5Mm Stereo Jack Connectors

    CAT connection, and optional PTT output to 50W PA kit (optional QRP Labs kit). The sockets may be a tight fit so insert them with care. When you are happy that the socket is neatly aligned and seated on the PCB, solder the remaining pins.

  • Page 76: Install Header Pin Connectors Jp3, Jp4 And Jp5

    3.54 Install header pin connectors JP3, JP4 and JP5 JP3, JP4 and JP5 are right-angled 2-row header pins. They connect the main QCX+ PCB to the front-panel PCB. A 12-pin strip of 2-row header pins is supplied. This needs to be carefully cut into sections as follows, using a wire cutter to carefully snap the plastic strip: JP3: 5-pin section •...

  • Page 77: Install Nylon Header Spacers If Required

    3.55 Install nylon header spacers if required If you plan to use the QCX+ in your own custom enclosure or if you wish to do initial testing without it installed in the enclosure, you may wish to install the supplied 6.5mm plastic hex spacers as support pillars in the four corner holes of the PCB.
  • Page 78 We now come to the assembly of the front panel. Here you need to pay particular attention since some of the components are installed on the rear side of the PCB. This photograph shows what the front panel PCB will look like, viewed from the front: This photograph shows what the front panel PCB will look like, viewed from the rear.

  • Page 79: Install Front Panel Pcb Resistors R44 And R65

    3.56 Install Front panel PCB resistors R44 and R65 R44 and R65 are 3.3K resistors. The colour code is orange-orange-black-brown-brown. Install them on the front-panel PCB as shown. 3.57 Install 270-ohm resistor R48 This resistor has colour code red-purple-black-black-brown. Note that it is a larger size than the other resistors because it is rated 0.5W dissipation.

  • Page 80: Install 1K Resistor R45

    3.58 Install 1K resistor R45 This resistor has colour code brown-black-black-brown-brown. 3.59 Install 10K resistor R46 This resistor has colour code brown-black-black-red-brown. QCX+ assembly Rev 1.11...

  • Page 81: Install 2X5-Pin Header Connector Socket Jp1

    3.60 Install 2x5-pin header connector socket JP1 This 2x5-pin header must be installed on the BOTTOM side of the front panel PCB! Install the 2x5-pin header connector socket on the reverse (bottom) side of the PCB, it will be connected to the pin header plugs on the main rear QCX+ PCB. Be very careful to solder this on the correct side of the PCB, it will be impossible to remove afterwards if you get it wrong now.

  • Page 82: Install 22K Trimmer Potentiometer R47

    3.62 Install 22K trimmer potentiometer R47 The 22K trimmer potentiometer must again be installed with the body on the reverse (bottom) side of the front panel PCB. Solder the pins carefully on the top (front) side of the PCB. This trimmer potentiometer is under the LCD module so it has to be fitted on the reverse side of the PCB.

  • Page 83: Install On/Off Switch S1

    3.64 Install On/Off switch S1 The On/Off switch has to be orientated the correct way, so that pushing the button in is “ON” and the button out position is “OFF”. Correct orientation is when the indentation pattern in the blue button body is right-hand side of the board when viewed from the front of the PCB assembly.

  • Page 84: Install Gain Control Potentiometer

    3.66 Install gain control potentiometer Remove the nut from the potentiometer, fit the shaft through the hole in the PCB, and carefully install the bolt and tighten with pliers. There is an anti-rotation tab on the metal case, which fits in the smaller hole to the right of the main shaft hole.

  • Page 85: Install Lcd Module

    3.67 Install LCD module The LCD module is soldered in place, it does not plug in using connectors. The 1x16-pin header connector is used to form the wiring between the front panel PCB and the LCD module, in the position indicated in orange in the diagram below. To achieve the correct spacing, insert two black 20mm M3 screws in the two holes of the LCD coloured in red in the diagram below.

  • Page 86: Install Knobs

    3.68 Install knobs Two black knobs are supplied, one for the rotary encoder and one for the gain control. When fitting the gain control knob, you should ensure that when the potentiometer is turned all the way anti- clockwise, the white pointer on the knob points to the bottom left corner of the PCB. This is the conventional alignment for volume control knobs.
  • Page 87 Photograph when viewed from the front of the radio: QCX+ assembly Rev 1.11...
  • Page 88 QCX+ assembly Rev 1.11...

  • Page 89: Install Microcontroller

    BEFORE plugging the board into the main QCX+ PCB. 3.73 Installation in optional Enclosure The QCX+ PCBs are designed to fit perfectly in the optional QRP Labs QCX+ aluminium enclosure. Installation is extremely easy and will be mostly intuitive.

  • Page 90: Connections For Basic Operation

    First bolt the front panel to the LCD module. This is the only tricky part of the enclosure assembly. Each of the four corners of the LCD module is bolted to the front panel using a 20mm black screw as shown in the diagram to the right. This is a quite fiddly operation particularly in the case of the screw next to the rotary encoder.

  • Page 91: Adjustment And Alignment

    enclosure, and you are disturbed or worried by the high temperature, then you may fit a small heatsink to the 7805 voltage regulator if you intend to operate at higher supply voltages. A 2.1mm DC connector plug is required; the center pin is + and the barrel is ground (negative). 2) Earphones The earphones can be any stereo earphones such as commonly used with audio equipment, mobile phones and so on, with a 3.5mm stereo jack plug.
  • Page 92 Unplug the antenna during alignment of the radio! Connect a 50-ohm dummy load such as the QRP Labs dummy load kit http://qrp-labs.com/dummy When using the TCXO module option, change menu item 8.5 Ref frq to 25,000,000. It is critical to this before any further alignment.
  • Page 93 Turn the rotary encoder until you see the alignment menu: 8 Alignment Now press the “Select” button, to enter the alignment menu. For example, for 17m operation, the alignment frequency menu item should already be set to a frequency in the CW section of 17m, as follows: 8.1 Align frq 18,120,020...
  • Page 94 Be wary because there can be more than one peak (more than one response of this simple band pass filter). So, tune the trimmer capacitor through its whole range, and determine the maximum scaling factor that you see. In my case here, it is 09. You may see 07, 08 etc, no problem. Then make the very fine adjustment necessary to peak the amplitude bar.
  • Page 95 20MHz system clock oscillator of the microcontroller. These adjustments can be made manually, or by connection of a GPS module such as the QRP Labs QLGx-series GPS receiver kits. However, since this calibration is a lot less urgent than the Band Pass Filter peaking and unwanted sideband cancellation, they are left until the description of these menu items in the operating manual.

  • Page 96: Experiments, Modifications And The Qcx+ Dev Kit

    GPS interface, 4-pin header with +5V, GND, RxD and PPS signals identified on the PCB silkscreen in the usual pinout of QRP Labs GPS connectors. Si5351A outputs, a 4-pin header with GND, 2, 1 and 0 indicated on the PCB silkscreen.
  • Page 97 2x5-pin connector to the front panel PCB (power, buttons and LCD control signals) 2x3-pin connector to the front panel PCB (rotary encoder signals and LCD data lines) 2x3-pin connector to the front panel PCB (audio volume control only) I2C bus, 3-pin header with SCL, SDA and GND indicated on the PCB silkscreen I-channel pre-amplifier output of IC5 Q-channel pre-amplifier output of IC5 Phase-shifted output of the I-channel path, at IC7A pin 1...
  • Page 98 JP25 2-way header with CAT port RxD signal; this can be used to reconfigure how and which signals are connected to the 3.5mm stereo jack socket (with JP23 & JP24) JP26 Input power, 3-way pin header providing Gnd and the +12V raw connection to the 2.1mm power connector, un-switched and un-polarity protected.

  • Page 99: Qcx+ Gps Interface And Ptt Output

    3.77 QCX+ GPS interface and PTT output The diagram shows the 3.5mm stereo jack socket connectors at the rear panel of the QCX+. In the case of the +5V/PTT, CAT and Earphones connections, all five pins of each +3.5mm jack socket are connected to a corresponding pad of a 1x5-pin header strip.
  • Page 100 The GPS produces two output signals, PPS (Pulse-per-second) and RxD (Serial data), in addition to ground. Optionally +5V may also be connected, in order to power the GPS module. A GPS such as the QRP Labs QLG1, QLG2 or QLG2-SE is perfect for this see http://qrp-labs.com/ql g2se There are two places to connect the GPS.
  • Page 101 GPS “RxD” connection via a 1K resistor. Similarly the paddle “Dah” signal is connected to the GPS interface “PPS” signal via a 1K resistor. The purpose of the resistor is only to prevent shorting GPS signals to Ground if the operator accidentally squeezes the paddle while the GPS is connected.

  • Page 102: Qcx+ Cat Port

    3.78 QCX+ CAT port The QCX+ CAT port allows a PC or other CAT-enabled host to control every aspect of the QCX+. Operation of this feature is detailed in a subsequent chapter of this manual. The connection diagram below shows the connections to the 3.5mm stereo jack socket connector on the rear panel of the QCX+.

  • Page 103: Circuit Design Of The Qcx

    5. Circuit design of the QCX+ Block diagram and summary This CW transceiver is a high performance, yet simple and low cost, analogue design. The transmitter uses a high efficiency Class-E amplifier which results in low current draw on transmit, and inexpensive transistors with no heatsinks.
  • Page 104 QCX+ assembly Rev 1.11...

  • Page 105: Synthesised Oscillator

    The circuit diagram (schematic) of the main PCB is shown on the previous page. The circuit diagram of the front panel PCB is shown below. Three 2-row connectors with right-angled pins on the main PCB connect the two boards; one has 2x5-pins and the other two, 2x3-pins each. Synthesised oscillator I always start with building the VFO of a radio.
  • Page 106 25 or 27MHz crystal. QRP Labs has always used the 27MHz crystal in our designs because it allowed us to obtain precise 1.46Hz tone spacing for WSPR transmissions all the way up to the 2m amateur band (145MHz). Those calculations don’t work out with the 25MHz crystal. This requirement doesn’t apply to this CW transceiver design but economics of scale means there are...

  • Page 107: Transmit/Receive Switch

    Transmit/Receive switch Since the receiver is entirely disabled during transmit, because of the absence of any local oscillator signals to the Quadrature Sampling Detector, the demands on the transmit/receive switch are considerably reduced. Now the circuit does not have to provide the massive amount of attenuation necessary to prevent the transmitter from overloading the receive circuits.

  • Page 108: 90-Degree Audio Phase Shift

    and LO input appears across each of the four integrating capacitors, with four phases at 0, 90, 180 and 270 degrees. The operational amplifier IC5a takes the difference of the 0 and 180-degree outputs and amplifies it, resulting in the I output of the QSD. Similarly, IC5b differences the 90 and 270-degree outputs to produce the Q output.

  • Page 109: Cw Filter

    In the real world, nothing is perfect – there are component tolerances to think about. The unwanted sideband suppression is maximised when the amplitude of the two paths is equal, and the 90-degree phase shift is accurate. To improve the accuracy of the 90-degree phase shift, R17 and R24 allow adjustment of the phase shift at higher and lower audio frequencies respectively.

  • Page 110: Audio Amplifier

    There are three stages of low-pass filtering and one stage of high-pass filtering. The first three stages retain the 2.5V “midrail” bias all the way through from the input transformer T1. The final stage IC9A is biased using the 5V supply (avoiding a few extra components to create a real 6V mid-rail at half the supply).

  • Page 111: Transmit Signal Routing And Pa Driver

    There is also a TX mute switch formed by Q7, another BS170 MOSFET. This was a late addition to the design: despite all attempts, I could not remove the nasty click on receive/transmit switching. The mute switch helps to attenuate it. The switch is operated by the microcontroller Receive/Transmit switch output.

  • Page 112: Class-E Power Amplifier

    The Clk2 signal from the Si5351A is used as the transmit oscillator as previously mentioned. It would have been easy to enable/disable the Clk2 output in software in the Si5351A chip configuration. However, this transceiver design also includes the built-in signal generator feature, for aligning the Band Pass Filter and adjusting the I-Q balance and phase adjustment controls.
  • Page 113 2) Reducing the effects of the transistor capacitances. Class-E has a resonant tuned circuit. The capacitance of the transistors, normally an unpleasant lossy aspect, is now a part of the tuned circuit. Class-E also has a reputation for being difficult to achieve. All those intense mathematics Google will help you find, don’t help.

  • Page 114: Low Pass Filter

    Low Pass Filter The transmitter output is rich in harmonics and must be followed by a good Low Pass Filter, to attenuate the harmonics and satisfy regulatory compliance. The standard, well-proven QRP Labs Low Pass Filter kit http://qrp-labs.com/lpfkit is used here. To save space and cost, the components are installed directly on the PCB, not on a plug-in board.

  • Page 115: Microcontroller

    microcontroller transfers the signal straight through from the key input, to the key output control line – but in other modes the processor must generate the keying signal. The component values set the rise and fall time. With the components shown, the rise and fall time is about 5 milliseconds.
  • Page 116 The ATmega328P was chosen because it has enough processing power and I/O to handle all the tasks required here. It is also common and inexpensive, and lots of QRP Labs products already used it, bringing economies of scale in both the kit preparation and the coding. The processor is operated at its maximum rated 20MHz system clock speed.
  • Page 117 The usual contrast adjustment trimmer potentiometer is R47 and must be set to obtain a readable display. The LCD backlight consumes about 30 or 35mA of current. The backlight could be connected directly to the 5V supply but this would somewhat increase the power dissipation of the 7805 regulator.
  • Page 118 All mechanical switches exhibit switch bounce, where the switch contacts generate multiple transitions for a short time when the switch is activated. It is common to see in many projects, resistor-capacitor networks to debounce switches (including the rotary switch). Simple debounce circuits involving a resistor and a capacitor inevitably involve a compromise when choosing the R- C time constant.
  • Page 119 The circuit fragment below shows the rotary encoder, and the three buttons (two tactile switch buttons, plus the button internal to the rotary encoder shaft) which are located on the front panel PCB. The input signal is pulled low by a 10K resistor R46. One side of all three buttons is connected to the I/O pin.

  • Page 120: Optional Gps Interface

    3.5mm socket for the keyer. The pinout of the 4-pin header exactly matches the one on the QRP Labs Ultimate3S QRSS/WSPR transmitter kit, and the QRP Labs QLGx-series GPS receiver kits. This makes connecting the radio to the QLGx GPS kit very easy, if you wish.

  • Page 121: In Circuit Programming (Isp) Interface

    5.15 In Circuit Programming (ISP) interface A 2x3-pin header is installed on the PCB to facilitate In Circuit Programming (ISP) of the ATmega328P microcontroller in future, if new firmware versions become available. Firmware updates can be done with a simple USBISP AVR programmer available from eBay for under $2 including international shipping.
  • Page 122 Audio ADC There are two audio connections from the receiver signal chain to the microcontroller. One is connected at the output of the I-Q balance adjustment potentiometer. In other words, the input to the CW filter. The second audio connection is connected after the final audio amplification gain stage.

  • Page 123: Voltage Regulator

    Self-test of Signal Generator and Frequency Counter Note that once the Signal Generator has been activated by scrolling to the Signal Generator menu item, and pressing the “Select” button to enable it – the Signal Generator remains active on the set frequency, until you press the “Exit”...

  • Page 124: Fault-Finding

    A 3-pin header pad connector could be fitted at JP26 to provide un-switched power to • additional boards; or if you wish to manage power switching in other ways, the thin trace between pins 1 and 2 of this 3-pin header could be cut. D3 (1N5819) provides reverse polarity protection and can be omitted if you wish, just •...

  • Page 125: Dc Voltage Readings

    Check that your IC2 microcontroller is correctly installed in its 28-pin socket, with the correct orientation (dimple on the chip matches the dimple on the socket and the PCB silkscreen). Check that all of the pins of IC2 are correctly inserted in the socket, not bent. DC voltage readings The following table lists the DC voltage read at various points around the circuit.
  • Page 126 Location Voltage Comment + supply terminal 11.98 As I already mentioned: a 12V supply Clk0 test pin ~1.70 The Clk0 pin in normal operation has a 3.3V peak-peak squarewave with 50% duty cycle. The DVM is measuring the average of that. Measuring here makes a lot of nasty noise in the audio.

  • Page 127: Rf Power Output Check

    IC9 pin 1 4.84 IC9a output IC9 pin 2 4.84 IC9 pin 3 0.65 IC9 pin 4 0.00 IC9 pin 5 0.67 IC9 pin 6 2.44 IC9 pin 7 2.44 IC9b output IC9 pin 8 11.67 IC10 pin 1 5.83 IC10a output IC10 pin 2 5.83...
  • Page 128 If you do NOT see any power output on key-down, then you probably have a fault in the Power Amplifier. A common mistake, as I mentioned previously during the assembly steps, is failure to remove or burn off the enamel insulation on the enamelled copper wire wound onto the toroids. Check the RF power wire touched to the BS170 drains first (see diagram).

  • Page 129: Measurements

    At supply voltages above 13.8V, check the temperature of the 7805 voltage regulator, which may need a heatsink as it dissipates more heat at higher supply voltages, if you are not using the official QRP Labs QCX+ enclosure and bolting the regulator to the heatsink. QCX+ assembly Rev 1.11...

  • Page 130: Transmitter Power Output

    Transmitter power output The transmitter RF power output varies depending on the power supply voltage. It is also dependent on band. Your results may vary depending on your Low Pass Filter inductor construction! If the cut-off frequency becomes too low, then you can start to get attenuation at the operating frequency.

  • Page 131: Class-E Power Amplifier Drain Waveform

    Class-E Power Amplifier drain waveform This oscilloscope chart shows the waveform at the BS170 drains (top, RED colour trace) and the input drive waveform, a 5V peak-peak squarewave (bottom, BLUE trace). The 40m band is shown. Upon ignoring the “ringing” artefacts due to poor ‘scope probes etc., the waveforms are correct for Class-E operation.

  • Page 132: Low Pass Transmitter Harmonic Output Filter Characteristics

    Low Pass transmitter harmonic output filter characteristics The Low Pass Filter response was not measured. The Low Pass Filter is the same as the QRP Labs Low Pass Filter kit module http://qrp-labs.com/lpfkit . Measurements of the Ultimate3S kit http://qrp-labs.com/ultimate3/u3s using these filters is on this page http://www.qrp-labs.com/ultimate3/u3info/u3spec.html Band Pass receiver input filter characteristics The following charts show measurements of the simple band pass receiver input filter...
  • Page 133 60m band 3dB bandwidth: 367kHz Insertion loss: 1.45dB at 5.357MHz centre Tuning range: 4.63MHz to 5.91MHz 40m band 3dB bandwidth: 514kHz Insertion loss: 1.97dB at 7.020MHz centre Tuning range: 6.04MHz to 8.36MHz QCX+ assembly Rev 1.11...
  • Page 134 30m band 3dB bandwidth: 645kHz Insertion loss: 2.67dB at 10.120MHz centre Tuning range: 7.93MHz to 12.47MHz 20m band 3dB bandwidth: 1,083kHz Insertion loss: 1.30dB at 14.020MHz centre Tuning range: 9.69MHz to 22.54MHz QCX+ assembly Rev 1.11...

  • Page 135: Quadrature Sampling Detector Bandwidth

    17m band 3dB bandwidth: 1,352kHz Insertion loss: 2.77dB at 18.120MHz centre Tuning range: 12.64MHz to 35.0MHz Quadrature Sampling Detector bandwidth The following chart shows the attenuation naturally provided by the Quadrature Sampling Detector from -20kHz to +20kHz from the Local Oscillator frequency. The narrow characteristic of this circuit is an advantage because it effectively adds an additional narrow RF bandpass filter to the receiver, preventing strong nearby signals from reaching the audio amplifier stages.

  • Page 136: Cw Filter Response

    The following chart shows the Quadrature Sampling Detector roll-off over the narrower range 0 to 5kHz. You can see that at the CW operating frequency 700Hz, the attenuation is insignificant; the roll-off of the QSD does not significantly improve the selectivity of the CW filter, but it does improve the intermodulation characteristics of the receiver.

  • Page 137: Unwanted Sideband Rejection

    7.10 Unwanted sideband rejection The following chart shows the measured level of the Upper Sideband signal (USB) and the unwanted Lower Sideband signal (LSB) when tuning the receiver through a strong test signal. The curves depend very heavily on the I-Q balance and audio phase shift adjustments, and these curves are from one measured prototype.

  • Page 138: Resources

    8. Resources For updates relating to this kit please visit the QRP Labs CW transceiver kit page  http://qrp-labs.com/qc xp 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 9.
  • Page 139 QCX+ assembly Rev 1.11...

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