Review: QCX Plus
We’ve reviewed the original QCX and the QCX Mini. Now Martin Evans GW4TPG describes the QCX Plus, a third product from QRP Labs.
We’ve reviewed the original QCX and the QCX Mini. Now Martin Evans GW4TPG describes the QCX Plus, a third product from QRP Labs.
The QCX Plus is a remarkable kit. I found it a lot of fun to build and equally fun to use on the air. The kit builds up into a small monoband 4 to 5W output CW transceiver with an incredible amount of functionality for the low price.
If you are used to having lots of features such as twin VFOs, digital frequency display, onboard keyer etc. you will not find the QCX Plus lacking. In fact, it also amazingly comes with a range of built-in test gear to aid fault finding and alignment. This includes, for example, a DVM and a signal generator. The QCX Plus is available for ordering in 80m, 60m, 40m, 30m, 20m or 17m bands.
I bought the 20m version of the kit when housebound after an accident in July 2020 as a project I could do as much or as little of as I wanted each day. It was a fantastic cure for lockdown!
QCX Plus Description
The original version of the QCX was developed back in 2017 to provide RSGB YOTA participants with a kit they could take home and use on the air. QRP Labs put together 500 kits to get the price down for YOTA and offered the QCX kit online shortly after. All 500 kits sold out in two days and in the three years since QRP Labs have sold over a whopping 11,000 QCXs. QRP Labs offered a new version earlier in 2020 of the QCX, the QCX Plus, which had some issues of the QCX ironed out. For example, the main PCB is larger, making the kit easier to build for OTs like myself. QRP labs also optionally offers a very nice custombuilt pre-drilled and laser etched enclosure specifically to house the QCX Plus, so building the kit into the enclosure results in a very nice looking transceiver with no metal bashing required − a big advantage in my case as I hate metal bashing.
The kit is also available ready built from QRP Labs (URL below) for an extra $45 if you don’t fancy building it yourself.
WhatYou Get
My kit took around three weeks to ship from at QRP Labs in Turkey. The kit does not come with a printed copy of the manual, this can be downloaded from QRPLabs.com and printed out if required. A word of warning, if printing the manual make sure you have lots of ink and lots of paper for your printer as the manual is huge. Every aspect of constructing, testing, aligning and operating this kit is covered in great detail. Hans has put a massive amount of effort into the manual to make building the kit as simple as possible.
The kit came in a small well packed box with all components bagged up with two PCBs and the optional enclosure. The small front-panel PCB contains the LCD display, switches rotary encoder and potentiometer, Fig. 1, while the larger PCB, Fig. 2, contains the majority of circuitry.
All parts are through-hole types for ease of construction. The QCX Plus has two very small surface mount ICs on the larger PCB, which are pre-installed on the main PCB before the kit is shipped so no small surface mount construction is needed.
Building the Kit
Despite the main PCB being larger than the original 2017 version I still found the kit had a lot of soldered joints in a small space so I would highly recommend an iron with a needle-type bit. To aid my eyes I also obtained a pair of watchmaker’s glasses from a well-known online source, which really helped to both identify components and in checking solder joints. I also wisely invested in some tweezers, side cutters and a small pair of long-nosed pliers from the same site.
The manual really had to be followed to the letter, each component double checked before inserting into the PCB holes, then inspected again to make sure I had the components in the right holes before soldering. Finally, the solder joints were checked with the watchmaker’s glasses before moving on. There is really only one chance to do this right. The PCB is through-hole plated, which makes correcting either a wrong value component or wrongly placed component using a desolder pump or desolder braid a very difficult
process. I ticked off each stage in the manual as I went along to make stopping and restarting construction periods easy. Building this kit needs time and patience to ensure issues are minimised.
The kit needed a few small toroid inductors to be wound. The most complicated toroid is L1, which has four separate windings and was by far the hardest part of the kit. This needed doublechecking before soldering. I found the easiest way to solder all the inductors was mounting the inductor onto the PCB first, then burning off the enamel underneath the PCB and tinning the inductor leads with my soldering iron set to the hottest setting before finally soldering the joint.
A quick continuity check with a DVM helps to be confident that the joints are good after soldering. All the other inductors for the lowpass filter (LPF) are comparatively easy to wind, provided time is taken to keep the windings tight and the right number of turns made before installation. Again, double checking before soldering helps.
After about 15 hours or so I reached the end of construction and the time came to move on to testing the kit.
TestingTime
This kit does not come with any connectors so a quick order to PW advertiser Bowood Electronics was needed to build up a fused DC cable and a BNC-to-SO259 adapter as my station is standardised with PL259/SO239s. I found Bowood’s service excellent and fast. Do not be tempted to use anything other than a fused DC cable in case of faults. A big PSU with an accidentally shorted kit would not be very good for morale!
I switched the kit on, the onboard processor booted up and the LCD display came to life after adjusting the brightness preset potentiometer exactly as per the manual. Time for alignment next! The alignment process is detailed in the manual and does not take long to complete. Do not be tempted to skip alignment because the receiver is very deaf until it has been aligned correctly.
It was at this stage I found I had my first issue, no audio in my headphones. Double checking all component values did not show any issues. However, I found I had a dry solder joint at the volume potentiometer. Reading the manual I found that the potentiometer pins do not go all the way through the PCB as they are bent at 90°. This is not an issue because the PCB holes are through-hole plated but when soldering, more heat than usual is needed because the potentiometer pins sink a lot of the heat away from the joint. To fix my issue I resoldered all three potentiometer pins and kept the iron on the joint for about ten seconds longer than usual.
The other issue I had was very similar. The mounting lugs for the PCB-mounted BNC socket needed more heat because the BNC socket sinks heat from the iron.
Alignment completed as per the manual, it was at long last time for a QSO. A quick tune around and I could hear an OE (Austrian) special event station calling CQ. I quickly swapped my station paddles to the QXC Plus and called him. It was at this point I realised my paddles were wired up with dits and dahs crossed! The software setting on my usual Microkeyer has the paddles reversed. Despite my awful backwards CW keying I managed a QSO with 599 both ways.
The QCX Plus receiver sounds very sensitive and compares well with my TS590G. The passband width sounds about right for my ears and I found it narrow enough for QSOs without QRM in most cases when the band is not too full.
Conclusion
The QCX Plus is a fantastic kit building into a very usable modern CW QRP monoband transceiver that would be equally at home either in the shack or out portable, etc. The QRP Labs supplied custom enclosure is very rugged and, in my view, the finished kit is small enough to be used for backpacking expedition work. The one issue the QCX plus has for backpackers is that the display and controls are not on top of the case
so the newer QCX mini might make a better kit specifically for backpackers and SOTA expeditions. As ever it pays to check before ordering which version is best for your particular circumstances.
The QCX Plus enclosure is probably large enough to modify the transceiver to take an internal battery pack although this is not mentioned in the manual.
Before using the kit on portable expeditions, it may be an idea to use some hot glue blobs around the toroid inductors to take some of the mechanical stress away from the solder joints. I did not do this with my kit so I can’t comment on the shift in inductance hot glue would make. It’s worth double checking with Hans first to see if this is an issue because the hot glue would be permanent and retuning inductors in situ would be very difficult if not impossible if they have shifted inductance beyond tolerance.
I would recommend any first-time builder try a less complex kit first, mainly to get experience with PCB soldering techniques, or build the kit with a mentor if at all possible. Having said that I think the kit is very buildable for most amateurs with an average amount of soldering experience.
The QCX Plus has a good online presence to help with most issues. There are loads of online ‘how to’s’ and videos and help is at hand to solve most issues. Hans at QRP Labs does answer queries via email if you get stuck.
The final photos, Figs. 3 and show the inside of the finished transceiver and a shot of it in my shack, alongside all the other gear, which gives an idea of size. I hope you enjoy building and using your QCX Plus as much as I did!