QRP-LABS QCX KIT BUILD

CW 40M TRANSCEIVER

PREFACE : I was recently at a Radio Rally and was moaning all day at how poor it was - full of old junk. I was helping out on one of the stands and had to stay there all day, otherwise I'd have disappeared within minutes of arriving.

Anyway, a friend had seen a BHI speaker on a stand for £100 but he said they wouldn't haggle, so I went over to beat them into submission - and it worked - so my mate bought the speaker. While I was there, I spotted a cardboard box with special Turkish stamps on it.

 

It kinda looked familiar, so I took a closer look and discovered that it was a small parcel from QRP-LABS similar to the one that my QDX had arrived in. I picked it up and saw that it was actually a QCX. That's a singleband CW 5W transceiver in kit-form.

I was quite excited because I just love building these sort of kits and so I nonchalantly expressed interest in it. From experience, I knew that after Tax, Import Duties and Postage, a QCX will cost a UK buyer around £100. If you want the aluminium case to go with it, the figure goes up to £130. 

Here was one with both items, boxed, unopened and even had a full colour printed spiral-bound manual (which you can't even buy) and I blagged it for £10!!!!  How good is that?? 

The seller warned me that the kit came from a Silent Key and he had no idea if all the components were present, but I knew already that there was nothing missing. It was obvious that the packaging had never been opened and it was probably one of those things that people purchase and hope to get around to building one day in the future.

It looks like the purchaser had also gone to the trouble (and expense) of having the Manual colour printed on A4 paper with spiral binding. Very nice! I was so pleased with my little find.

When I sat down to read the manual for the first time, I could see that the original buyer had done the same thing. He had very obviously gone through it and highlighted the very important parts which need special attention during the build. I'm guessing he'd read it a couple of times because there were handwritten notes in different ink/pencil. They were very neatly written and it showed that he had a previous kit-building experience.

My inquisitive nature led me to find out more about this Silent Key. I could see from the packaging that the name and address had been hidden with black marker pen, so I took a photo and then over-exposed it in software, which partially revealed the text.

I could just about make out the postcode, so I searched QRZ for amateurs in that immediate area and up popped Mark Raybould - G3XYS. He had lived in the High Peak district of Derbyshire, about 30 miles from me. 

I learned from his bio that he was first licensed in 1968 and was very much a QRP man and greatly enjoyed SOTA activities. I discovered too that he was the very first person to activate Moel Eilio, GW/NW-022 in Snowdonia, back in 2002. 

He also had an American callsign (NS1Q) and had family over there in Vermont, but that's as much as I know at this time. I was very pleased to find this connection to the QCX and it felt good to know that I'd be finishing off one of Mark's projects for him. Something which he was sadly unable to get around to doing himself - possibly due to ill health?

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THE BUILD : Bear in mind that this is the original QCX and not the later QCX MINI. Now this kit represents a significant increase in complexity compared to the kits I've built before. Please bear in mind that I have no real knowledge of electronics and I'm writing this post to show how a beginner might cope with this kit.

There are a lot more parts than I'm used to (with almost 300 solder joints to complete) and I'll have to pay very close attention to the build-guide. Looking at the original packaging and post-mark, I can see that this was purchased in 2018 and thankfully it came with the REV.3 manual already printed out.

The last revision of the QCX is REV.5 but a quick glance at the website indicates that the Rev.3 can be brought up to date during the build with changes to components (or additions), but looking through the alterations I might not bother. 

Rev 4: (31-Oct-2018)
1) Changed C21 and C22 to 1uF (previously 10uF) to reduce click on Tx/Rx switchover
2) Kits shipped after 12-Apr-2019 changed R41 from 470 to 150 ohms; R42 from 1K to 1.2K; C31 from 1uF to 2.2uF; to improve key-shaping.
3) Kits shipped after 12-Apr-2019 also changed R21 from 7.5K to 10K to allow phase compensation for larger range of component tolerances. 

Rev 5: (06-Jan-2020)
1) Removed components R49, R50 and C39; R53 changed from 1K to 3.3K; the components were not needed since AUDIO2 DC bias is 2.5V already
2) Added R49 (1K), R50 (270-ohm) and D7 (1N4148) which are to implement a serial port for the CAT control interface

There is one mod which does look interesting and that's something which was designed by a 13yr old American operator called Maxwell Moran (W3LLA). This bright young man came up with a way of turning the QCX into a WSPR transceiver! It works by bypassing the CW Filter - and it's switchable, so you don't lose any of the QCX's original functionality.

THE FIRST JOB though is to layout and organise all the components. It’s quite a laborious task checking not only that you’ve got all the required bits and bobs, but also identifying the values. You need to know if anything is missing early on, so you can make arrangements to obtain a replacement. Nothing worse than getting to the end and finding you can’t complete your kit.

It turns out that there were a couple of 10uF electrolytics missing from my kit but thankfully, a friend from Bolton Wireless Club said he had some spare (thanks M0UFC).

There was still a bit of a puzzle to solve though, because I still had more components that were listed in the printed manual. What was going on??

I decided to examine the PCB and it was at that point I realised that this kit was actually a REV.4! It seems that the original buyer had mistakenly downloaded the wrong manual. I can fully understand why, because it's really quite complicated due to the number of manual-revisions and release dates.

Anyway, all the components now made sense and I wasn't short of anything, so I started the build.

The very first job is to wind the T1 transformer which can be really tricky depending on the band you've chosen. The 20M model looks nice and easy, but I have the 40M version with an additional 14 turns to go on (38+5+5+5).

The T1 goes on first because it makes the job much easier without any other components on the PCB. The manual suggests that you wind the T1 in a single run and then cut loops to create the three 5-turn sections, but I found it easier to wind the 38T, then three separate 5T's.

Regardless of which way you wind it, you're in for some fiddly work. Make sure you leave long legs so that installation is less awkward. Don't worry - there's plenty of spare wire.

IMPORTANT!!! As per the manual - "the four windings on T1 must all be in the same “sense”. There are two ways to wind toroids. You might call them left-handed and right-handed; clockwise and counter-clockwise; whether the wire goes through the toroid from top to bottom, or from bottom to top. Whatever you call it, all the four windings have to be the same, to be sure to get the phasing to the quadrature sampling detector correct".

WINDING TIP : I was pretty sure I'd counted the 38 turns as I was doing it, but when I took a photo and saw it on a large PC screen, I could see that I'd only done 37, so I added another. Checking in this way allows you to easily make a correction instead of pulling your hair out after you've soldered it onto the PCB. At this stage you don't need to worry about neat spacing of the turns - you can sort that out as you're installing it.

Getting this toroid into the PCB is quite a job! There are eight straggly legs to control and it's easy to get into a mess and maybe even put the wrong wire into the wrong hole.

The ends of the 38T wire is pretty obvious to locate - the real problem is identifying the ends of the three 5T wires. To aid me with this, I put black Marker Pen on the legs of the middle 5T wire. That helped enormously. If I'd had different coloured enamelled wire, that would have been even easier!

I suggest that you start the installation by getting the innermost wires located first - 8, 4, 6. Once they're in, the rest of the job is much easier... 

With all the legs in, check that all the turns are neatly spaced and do a continuity check on the 4 wires to make sure they're in the correct holes. Once that's done and you're 100% happy with the spacings and location, you could insert a small blob of HotGlue in the center of the T1 to keep it fixed to the board and to stop any of the windings from moving around while you're snipping the legs and soldering them in place.

The manual recommends that you cut the legs down so that they're about 2mm proud of the PCB and use the Soldering Iron's heat to burn off the enamel.

Personally, I prefer to carefully scrape most of the enamel off with a sharp scalpel from the underside of the PCB before snipping the wires and then solder the 2mm legs for the recommended 10 seconds to burn off any last remnants. This method worked very well for me on my QDX but I'm no expert, so do what works for you.

Once T1 is in place, you can revert to following the start of the manual and install components accordingly.

It's worth noting that Hans has every right to tell you to check your work once, twice and even three times!  I made a mistake very early on by putting a ceramic capacitor in the wrong place. Luckily, I managed to desolder it and relocate it. 

I got into the habit of placing the components in the pcb, then taking a photo of each stage and that process slows you down a little and prevents you from rushing ahead.

The rest of the build was very straightforward - there’s nothing especially tricky - there’s just lots of it!  I simply followed the guide and before I knew it, the kit was built and ready to power-up and carry out the alignment/setup.

Sadly, when I powered up I discovered that there was a problem with the display - only the top row of text-blocks was illuminated, which (according to Hans’ trouble-shooting guide) means that IC2 is not communicating properly.

Needless to say, I checked, double-checked and triple-checked that the chip was seated properly and all pins were engaging with the socket. I also went onto IOGROUPS and got some more trouble-shooting guidance from the members there, but nothing has found the source of the problem so far.

It could be that the IC2 chip itself is faulty, so I may order another (£3).

It’s a really disappointing result, but I’m not giving up on the kit even though it only cost me £10. Some might say that people like me (with little or no electronics knowledge) shouldn’t be building these kits and I do understand their point of view, because I feel bad pestering people for help. It’s like asking a mechanic to help you sort out the mess you’ve made of your amateur engine-build 😂

Anyway, I will try to get it going and will update this page accordingly. If I manage to sort it out, the method will maybe help out someone else who has a similar problem with this lovely kit.

Bye for now!

Tom, M7MCQ.