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 specialized design for a 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 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 are to make it smaller. The following table is a comparison with the QCX installed in a BaMaTech aluminum 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|
The dimensions for QCX-mini assume installation in the optional aluminum enclosure, which will be the same aluminum 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 aluminum 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 Lab’s participation in the QSO Today Virtual Ham Expo.