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QCX: a feature-packed, high performance, single-band 5W CW transceiver kit, with WSPR beacon and built-in alignment/test equipment. Available for 80, 60, 40, 30, 20 or 17m bands. It has rotary encoder synthesised tuning, VFO A/B/Split, Iambic keyer, CW decoder, and more...

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The "QCX" is a 5W, single-band, high performance CW transceiver kit with WSPR beacon, and built-in alignment/test equipment. It is available for 80, 60, 40, 30, 20 or 17m bands. See below for the long list of features! This is a kit of parts that you assemble yourself. There are NO surface mount components to solder (two SMD ICs are already factory pre-soldered).

There is also an enclosure kit available (see photo, right). 

Please see QCX Frequently Asked Questions page for any queries you have. In case of any problems, please see the QCX trouble-shooting page


Features


Assembly and operating instructions

The assembly document includes circuit diagram and a detailed description of transceiver operation. Please download the correct assembly instructions for your PCB revision. The PCB revision is the number in the bottom right corner. 

NOTE: PCB Rev 4 kits shipped after 12-Apr-2019 have four component changes. Make sure you have the correct manual version. There are four component value changes in these kits shipped after 12-Apr-2019, which are explained on page 7 of the latest 1.12 manual dated 20-Apr-2019. 

DOWNLOADS:


Firmware

There have been several firmware updates since the 21-Aug-2017 launch of this QCX CW transceiver kit. These provide enhancements and bug fixes. If you have an AVR programmer you can update your firmware using the on-board programming header. The firmware version history and more information are on this page (click!).


Modifications

CLICK HERE for a Modifications page, various improvements you can easily make to your QCX radio.


PCB Revisions

There have been a number of PCB revisions, these included minor changes which improved some aspect of the QCX or enabled new functionality. 

Rev 1: Original version, August 2017

Rev 2: Minor changes

Rev 3: (26-Jan-2018)
1) Modification to improve contrast potentiometer adjustment; added R65 (3.3K) (described here).
2) Modification for unreliable microcontroller startup included as standard (described here). 
3) Modification to prevent occasional PA instability; added R64 (10K) (described here).

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


Photographs

These photographs show the prototype kit, both with and without the LCD module plugged in. The powered-up kit shows the radio's Frequency Counter feature measuring the frequency generated by its Signal Generator feature.

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Builders' enclosure photographs

A common question about the QCX transceiver, is about what case to use for it. There is not an official QRP Labs enclosure for the QCX. But many people are finding their own solutions to this question. 

For photos and information about what some constructors have done about enclosing their QCX, visit the QCX builders' gallery page!


Shipping updates

QCX kits are being shipped within typically 1 business day of the order. 

Serial numbers are listed on this page


ARRL Review of QCX in August 2019 QST issue

Paul N1II reviewed the QCX transceiver in the August 2019 issue of the ARRL monthly publication QST. 

CLICK HERE to read the PDF (497K file)

Reproduced with the permission of the ARRL. Copyright ARRL.

Visit the ARRL website here


Videos and reviews of QCX

The kit was originally designed for the RSGB Youths On The Air summer camp buildathon in August 2017. This RSGB YOTA Vlog video, shot at QRP Labs booth at Friedrichshafen 2017. 

For more videos and reviews please see the QCX videos page!


 K9YA Telegraph, March 2018 edition, review by Philip K9PL

The K9YA Telegraph's March issue has an article on the QCX by Philip K9PL, sub-titled "QRP Labs Moves the Goalposts". Philip concludes his 3-page article: "...the QCX behaves like a monoband, QRP slice out of a QRO high-end rig with deep, deep menus - very innovative and a joy to operate.

The K9YA Telegraph is a free monthly Ham Radio eZine, see http://www.k9ya.org/ for details.

Philip K9PL has provided a PDF of the article with permission to reproduce it on the QRP Labs website. CLICK HERE to read it!


Common Issues

The following issues have arisen more than once, and have the solutions indicated. 

Issue Solution
Microprocessor does not boot up at power-up, requires switch-off/switch-on again to power up properly See modification here
Power Amplifier instability results in low or unstable power output, or high current draw, or blown MPS2907 See modification here
LCD contrast fluctuates on transmit Check for LCD module frame short to L2, see here for details
Low output power on 20m (or other band) LPF inductance is probably too high, resulting in attenuation at the transmit frequency. Remove turns one at a time from LPF inductors L1, L2, L3
No power output at all Check continuity through L1, L2, L3 and other inductors L4 and T1, as advised in the manual. Probably one or more have not properly burnt off the enamel so there is no electrical connection. 

More troubleshooting


Phase noise measurements

For a detailed page about phase noise measurement techniques and the measurements on the QCX in particular, CLICK HERE.

The transmitter output phase noise measured was within 1dB of the -135 dBc/Hz at 10 kHz and 50 kHz spacing measured by ARRL in their QST review (see above). This level is considered GOOD. No improvements were found to get better phase noise performance from the QCX. 


Performance measurements by Ed WA4MZS

Ed made some interesting measurements of his 40m QCX serial number 354 (see also builders' photos page). 

Spectrum analyser close-in and wide screenshots:

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Board dimensions

The following diagram shows some dimensions of the QCX PCB. Important notes:

Specific notes about the LCD module:


QCX 3D model by Eugene UR5TLZ 

See QCX 3D model page