QCX-mini is coming soon!

(This article is written on 11-Sep-2020)

QCX-mini is a response to quite a few comments on the new QCX+ kit, from people who want to take it out portable for SOTA operations and other portable operations, and complained that the QCX+ is bigger and that they preferred both the smaller size, and the format (controls and display on the top face) of the original classic QCX. Generally speaking, QCX-mini is not an experimenters radio; there is not a lot of spare space inside the enclosure and most of the circuit is SMD. QCX-mini is a specalised design for minimum size, intended for portable operations. 

QCX-mini uses basically the same schematic as the QCX+ and the same firmware chip. Operation and performance are the same. This is NOT therefore being undertaken as a large, time-consuming project. Specifically, the scope is restricted to keeping it QCX-compatible, to minimize development time. Just make-it-smaller. The project therefore is a mechanical re-engineering task, with some documentation towards the end, and a small firmware change to facilitate the configurable LCD backlight.

QCX-mini Specifications

QCX-mini has almost the same circuit (schematic) as QCX and QCX+. It also uses the same firmware chip, in the same 28-pin DIP package. The operating characteristics and performance are also the same. QCX-mini has the same connections as QCX+, even including the CAT and PTT connectors. The primary difference and motivation is to make it smaller. The following table is a comparison with the QCX installed in a BaMaTech aluminium enclosure. All dimensions are excluding protrusions (controls and connectors). 

Radio Dimensions (cm) Dimensions (inches) Volume (cm3) Volume (inches3)
Classic QCX 11.2 x 9.4 x 3.5 4.4 x 3.7 x 1.4 368 22.5
QCX+ 10.6 x 5.5 x 14.7 4.2 x 2.2 x 5.8 854 52.1
QCX-mini 9.5 x 6.3 x 2.5 3.7 x 2.5 x 1.0 150 9.1

It can therefore be seen that while QCX+ is 2.3 times larger than QCX by volume, QCX-mini is 2.5x smaller than QCX by volume. QCX-mini is 5.7x smaller by volume, than QCX+

The dimensions for QCX-mini assume installation in the optional aluminium enclosure, which will be the same aluminium extrusion profile as the 50W PA kit, but cut shorter (92mm) and of course drilled and laser-etched differently. 

QCX-mini has the following changes, to implement the smaller size and other features:

  • Extensive use of 0603-sized SMD components, which will be factory pre-assembled. The inductors are still toroids and the NP0 capacitors in the RF section are still through-hole type, the same as in QCX+. The BS170 and MPS751 transistors are also still through-hole and bolted to the PCB by a nut, bolt and washer just like on the QCX+
  • Yellow/green LCD which is highly readable outdoors, and readable without the backlight (to reduce current consumption). This is the same high quality LCD made by the QY brand, as used in all QRP Labs kits; it has two backlight LEDs rather than the usual single LED found on cheaper LCDs. Since the LCD is the same size and style as the original QCX/QCX+ kits, it offers the same easy to read, large text.
  • Smaller gain (volume) potentiometer
  • Multi-PCB sandwich assembly, designed to slide into an optional aluminium enclosure
  • Smaller, all metal, high quality, robust BNC connector
  • Lower current op-amps for ICs 6, 7, 8, 9 and 10 to reduce overall power consumption

Additionally the QCX-mini is compatible with the TCXO module option designed for the QCX+. In the following photographs you will see that I have installed the TCXO board on the QCX-mini sited over the Si5351A, in the same way as is done on QCX+

Although it is very compact, QCX-mini will be I think, faster and not more difficult to build than the QCX+. The circuit is basically the same but many of the components are SMD and are already factory-installed. That leaves the coils to wind and install, the NP0 capacitors of the RF section, the connectors, controls, IC sockets and a few other through-hole components. 


I discussed the QCX-mini development in a live video recording Q&A Zoom session recently, as part of QRP Labs participation in the QSO Today Virtual Ham Expo. 

Dev Update 1: 11-Sep-2020

Prototype boards arrived! Some preliminary assembly was possible with parts on hand, enough to verify the boards fit together properly and boot up the QCX, operate the Si5351A and do some testing on the visibility of the display in outdoor conditions. This article also explains more about how the QCX-mini boards fit together etc. READ MORE...

Dev Update 2: 24-Sep-2020

SMD components arrived on Monday 21-Sep-2020 and two prototypes have been assembled, debugged, tested and adjusted. The first QSO with the QCX-mini was with Feri HA2EOU on 24-Sep-2020. READ MORE...

Dev Update 3: 25-Sep-2020

The enclosure prototype was delivered on Thursday evening 24-Sep-2020 and I was excited to see that everything fit perfectly as I had planned it. I also made a weight comparison and current consumption comparison. READ MORE...

Dev Update 4: 28-Sep-2020

This article details work to resolve the microphony problem. I am comfortable that the problem is solved and the next step is to redesign the PCB to accommodate the changes. READ MORE...

Dev Update 5: 30-Sep-2020

QCX-mini development phase is complete! QCX-mini has now entered the kit manufacturing phase! READ MORE...

Dev Update 6: 16-Nov-2020

Good news at last... after several unexpected delays, all component sourcing, custom-component manufacture, PCB and SMD Assembly steps are now completed! Next is shipping to me!READ MORE...