QRP-Labs QCX+ 30m CW

This page was last updated : 11-May-21 22:28:15


This page is work in progress and may be updated frequently (last update : 2021-05-10 11:55 UTC). 

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Loving the kits from QRP-Labs, and when Hans Summer announced his new QCX+ CW tranceiver I knew I wanted to buy and build one. And when he added it to his webshop I didn't hesitated for a moment and ordered the 30m kit with a few other nice QRP-Labs kits (when your ordering and have to pay shipment, order more). 

Postman only had to ring once

And after waiting for almost 2 months (Hans didn't anticipate the popularity of the QCX+ with the enclosure), the mailman just rang once and brought me the long awaited package from #qrplabs .

Content :



Everything nicely packed and labeled. 


Having some time, I started with the dummy load kit and finished it within 25 minutes (see page).

Lets see if I can find some me-time the next few weeks to build the QCX+. Oh which I did and in 2 evenings the kit was build, aligned, calibrated, and ready to use.
But then 30m was quite as cemetery. 

At least we have the pictures :-) 

The manual

As with every kit which Hans sells, the also was a very nice manual for the QCX+ (link).  The first 2 chapters contain a Introduction with technical specification and the full Parts list of all components in the kit. Chapter 3 contains a list building general guidelines, images of the PCB layouts (track and component placement) and photo's of a finished QCX+ allowing to kit builder get a idea about what to expect. And after sub chapter 3.1 Inventory parts helping the starting kit builder to identify parts, the fun starts.

Let start building 

In the QCX+ manual there is big differenice against the QCX manual, which that Hans decided it is best to start with "Wind and install transformer T1". A detailed description about the transformer in component placement, schematic, a drawing and a photo helps the (starting) kit builder wind the transfomer.   


With the coil winded and soldered in place the first user installed part is done.  


Next chapter in the manual is chapter 3.3  instruction for installing a IC socket for the ATMEGA328P. I don't used the supplied socket but use a little more expansive model.

Although Hans in Chapter 3 explains his vision on the use of IC sockets for the rest of the integrated circuits,

Some people like using IC sockets, some don’t. Undoubtedly there is a cost impact, of course. Personally, I believe that on average, the use of IC sockets causes more problems than it solves. They create the potential for bent pins that don’t make contact properly, hidden shorts under the socket, issues with increased lead length, etc. Accordingly, the remaining ICs are soldered directly into the PCB without IC sockets. Please forgive me if you disagree.

I personally like to use them because sometime thing just break, release magic smoke, stop working, etc.  So Hans, if you read this, I would like to quote the following passage of the manual : "please forgive me if you disagree."  ;-) 

So the instead of the integrated circuits indicated in  chapter 3.4 I installed IC Socket for all of them. 


In the chapters 3.5 until  3.18 all the capacitors grouped by value and shown where the place them. 


In the chapters 3.19 until  3.20 all the diodes grouped by value and shown where the place them. 


In the chapters 3.23 until  3.39 all the resistors are grouped by value and per value shown where the place them.

In the picture below you also see  XTAL1  from chapter  3.21, the two 47uH inductors  from chapter 3.40, the capaciitors from chapter 3.41 and 3.42 and the 30pF trimmer capacitor C1 from chapter 3.43


In the chapters 3.44 and 3.45 MPS751 and all the BS170 are installed.  In the picture below you also see 2x3-pin in-circuit programming header from chapter 3.46.


At chapter 3.47 installing the power connector I started to change direction. To get the power connector correctly alligned, I first installed the RF output BNC connector from chapter 3.52 and the  3.5mm stereo jack connectors from chapter 3.53. When you install the RF output BNC connector, place the other connectors and use the back plate as a alignment tool and use a dc plug to align the power connector, everything is exactly where it should be. 


Check, check, double check. And let solder. Oh wen when you at it, place the 7805 voltage regulator as described in chapter 3.48 align it with the hole in the backplane. You can even use the supplied bold and nut.


Everything exactly where is should be.  


For now I skip chapter 3.49 - 3.51 (about winding the toroids L1..L4) for later. Winding toroids when you a bit tired, is a bad thing. 

Installing the optional TCXO module

In chapter 3.69 Hans describes the function and installation of the TXCO module option.

Instead of using three cut-off component wires I used 3 pins of a leftover header I have. 



Front panel PCB

The building of the front panel is very straight forward as shown in the manual and in the pictures below.  



When installing the on/of switch, pay attention to the position (the gap should be on the right) so the power is on when the button is pressed. These buttons don't like to be de-soldered (trust me, i found out the hard way on a LC meter project using the same switch). 


Almost there


And forgot to take a picture about aligning and soldering the LCD :-S

Now installing every thing according to chapter 3.72 Installation in optional Enclosure


Looks good doesn't it ?  


It even gets better.  


And better. 


Almost there.

Did you remember that I skip chapter 3.49 - 3.51 (about winding the toroids L1..L4)? Well that was one thing I had to do. So when I checked if there are no shorts in the power circuit (5V and 12V) and then installing all the integrated circuits as described in chapter 3.70 (ATMEGA328P) and chapter 3.4 LM4562 and 74ACT00, I wound the toroids as described in chapter 3.49 - 3.51.

Powering it up 

I setup my benchtop power supply to 12V and a current limit of 500mA (just in case something goes rouge). Following the alignment procedure in the manual in less then 10 minutes everything was ready to go.    



Checked the power output with my power meter (a nice 3 W) hooked it up to a antenna and . . .
then there was no CW activity on 30m :-( 
Gave a few times a CQ but no takers. Did saw my CQ appear on a few EU CW skimmers. It should be fine. 


One small note and how to fix it 

There is one thing I found out I didn't like when using the stock enclosure. When the front and back panel are installed, the connectors of the front tend to retract and make a gap of aprx 1.2 mm. Which may not be a problem, there is still contact but it's not what you would expect or like to see.

Personally I don't like the LCD to be exposted, so I used a piece of 1 mm thick plexiglass and cut it to the shape of the LCD display, drilled the 4 holes and added it between the LCD and the front plate. Protecting the LCD glass from touches, dust etc.  and as a bonus, the gap between the front panel connectors and the mainboard connectors is gone.  


Bought 30m QCX+ made it a 20m QCX+

Because there is a lot more CW activity on 30m and I don't have a resonant antenna for it, I decided modify my QCX+ for the 20m band. 

Steps included :

  • Remove C5
  • Replace C27 and C28 with 180pF 
  • Replace C25 and C26 with 390pF
  • Remove 3 turns from L1 and L3
  • Remove 3 turns from L2
  • Remove 4 turns from L4
  • Remove 1 turn from the 4 turns windings on T1
  • Preform a factory rest (menu 7.11 enter 17) 
  • Again enter 25Mhz in Ref. frq (menu 8.5)
  • Adjust peaking BPF (menu 8.7)
  • Adjust I-Q bal, Phase LO and Phase HI (menu 8.8, 8.9 and 8.10) - note : i didn't need to they where still prefect.

Checked the power output with my power meter (again a nice 3 W) hooked it up to a antenna and enjoyed listening to a lot of CW QSO's on 20m.

Tilting feet


I really love the original case. But when you have it on a desk, the ergonomics aren't that good. Trying to turn the dials can be very uncomfortable and on groups.io/QRPLabs, Larry N6NC described the same problem. He asked  if some one all ready made a 3D printed stand for the QCX+ and I showed hem the tilting feet I made for my uBITX. These are rather large so I took a moment design a dedicated set for the QCX+.  It's not finished yet (maybe I want to bar to be a little taller, giving the case a large elevating angle. 


The set consist of 2 round feet and a lifting bar (how do you call that in English??).

Note : I used yellow material for prototyping. That way I can see the wires and details with my own eyes without aditional light and magnification.


The lifting bar fits really nice in the feet.


Using thin (and strong) double sided tape I placed the set under my QCX to see if the elevated angle was ok.  


The angle with this lifting bar is aprx 15 dgr. 



The lifting bar can  flipped underneath the QCX when needed. 


In the 3D design I have added 3 different lifting bars with different heights. Images below show the short, middle and tall version.  




So far it looks good to me. I made the lifting bar in various height to check what the most comfortable elevated angle is. Also the feet is in 2 models, one which let the lifting bar in a angle 120 dgr (shown in the pictures above) and one in 90 dgr (shown in the pictures below).  

The front panel PCB assembly of the QCX+ is all away to the bottom of the case. Meaning that drilling the holes should be done very accurate not to interfere with the front panel PCB. So I added 2 drilling template to the 3D design. One (10mm) for when you have a 1.5mm Plexiglas screen in front of the LCD like I have and one (8.5) when you don't have it. This is needed because the front panel 



Check check double check. 


Nicely drilled holes exactly on the spot (remember that the drilling template can be used only once when the drill gets hot). 


Pictures showing the use of the 90 dgr angle feet. Because the case is lifted enough it wont tip forward. 


We need to install the front panel assembly first because the bolts will prevent sliding in the front panel assembly (the PCB will hit the bolts). 


Everything together. 


After using the QCX for a few hours I decided to finalize the design. Although I like the yellow color for a lot of tools and parts, I printed  a set of straight angle feet and a medium height lifting bar in grey color. Giving it a little more matching for the black enclosure. 

I used a M3 thread tap to cut a M3 thread in the enclosure (the 2.5mm holes where perfect for that) and used short M3 bolts to mount the feet.


For me the aprx 18 dgr operating angle is very comfortable. 



All done. 

I made the design publicly available so you print your own but licensed it Attribution-NonCommercial-NoDerivs 3.0 Unported (CC BY-NC-ND 3.0).
Meaning : 

  • Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
  • NonCommercial — You may not use the material for commercial purposes.
  • NoDerivatives — If you remix, transform, or build upon the material, you may not distribute the modified material.

It's not to be childish but it now happened a few times that a 3D design I made was sold by other people just because is was "Open source, so I can do anything I want with it" without any credits or even a token of appreciation

When you want it to be used Commercial, please contact me.   



A Electron Volt QCX Auto Gain Control Kit

In the QRP-Labs groups.io there is a thread about a AGC circuit proposed by Jim AJ8S. Electron Volt Limited made a very nice kit from this design and sells that a reasonable price in there webshop.

For my QCX+ and QCX-mini I ordered two of those kits and within a few days the postman dropped of a envelop from the UK containing two ESD sealbags containing the kits. I printed the manuals, put them into a binder with a schematic of the QCX+ and QCX-mini and the PCB from the QRP-Labs manuals. So when I had time to install them, I had everything in place.

On my parttime day, it was windy and raining, so perfect weather to take a seat in the shack and build in these kits. Our shack-cat Moppie couldn't agree more.


When opening my QCX+ I forgot about the development board I installed in it.  


So first thing I had to figure out was if the AGC could fit underneath the development board. But luckily there is plenty of space above the 3.5mm chassis parts.


Then I followed the instruction manual soldering the wires to the AGC PCB. 


Installed the shrink tube, applied the double sided 3M tape and tested if it all would fit. Well it does. 


 And then I started to change paths from the manual. I pulled all the 4 wires from the AGC through the JP18 (headphone breakout) holes.


So I could wire up the ground and the +5V to the JP1 GPS breakout. That way we keep the +5V away of the RF. The ground could be picked up from JP18 as described in the manual.


Following the manual I installed the blue and purple to the correct position and from the left over double side 3M tape I cut of 2 small pieces and applied them on the PCB to hold the wires in place (don't worry, they will be covered with extra tape). 


Using a small piece of insulation tape I fixed the wires. 


Then it was adjustment time. To bad the wasn't a lot of activity on 20m this morning, but there where enough stations to do a initial adjustment. 

The way I adjusted it (with connected antenna): 

  1. Turn volume control to 1/3
  2. Turn the trimmer full CW, notice the background noise.
  3. Turn CCW until background noise drops.
  4. Turn slowly CW until the background noise is aprx as was at 1.
  5. Seek week morse station and when needed adjust for good readable (because we adjusted to background noise there shouldn't be much to adjust).
  6. Seek strong morse station and adjust CCW until acceptable. When needed repeat 4..6 until you find the correct AGC setting for you. 

The picture below is showing the end position.  


Because I have the (un-used) development board installed, I drilled a hole in it to allow post-installation adjustment of the AGC when needed.


So far the installation of the AGC on my QCX+. Next will be the QCX-mini. 

My thoughts on this kit :

  • Pro : A very nice addition to the QCX line because which will probably safe some eardrums during a contest or when a local QRO stations is coming back to you.
  • Pro : The price is very reasonable.
  • Pro : The kit is well documented. 
  • Pro : Easy to apply (unless you uncap-able of soldering and reading manuals / schematics).
  • Pro : looks easy to adjust, time will tell if I did it ok.
  • Con : nothing I can think of. 

It's nice to see that there are more and more people building small (and effort-able) kits for the hamradio community.


Next steps

The problem with building kits is that your never done building and/or modifying them. So next steps include : 

  • Safe up some money to order myself a QRP-Labs 50W amp for 20m.
  • Try to find a similar looking case to build in a small power supply with speaker (got it)
  • Build a small power supply with speaker 
  • Use the development board (or other PCB) to add a build in Arduino PS2 keyboard enabled morse keyer based on the NanoKeyer (link)  

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