QCX Auto Gain Control Kit

Price reduced until current batch exhausted.

Note: All orders since 2021-06-14 are REV B kits. REV B is mostly identical to REV A, except the addition of the wiring harness. REV A & REV B instructions can be found under the 'Attachements' tab of this product page.

The kit is based upon the circuit proposed by Jim AJ8S on the QRP-Labs discussion forum: thread here. Note: Electron Volt Limited has no affiliation with QRP-Labs, we just own a few QCX radios and hoped we could help make this mod more accessible.

The circuit has been miniaturised into the smallest size reasonably achievable (at low cost and low volume production) to make it as easy as possible to fit inside the QCX mini. Other than switching to SMD devices, the only change is the addition of a fixed 1.8kOhm resistor between the 5V input and the trimmer resistor. This limits the maximum voltage possible at the tantalum capacitors and makes the range of the trimmer slightly more useful.

The AGC kit consists of: AGC PCB REV B (fully assembled and tested), custom 20cm wiring harness with pre-fitted connector, heatshrink tubing, double sided tape, and an anti-static bag. You will need general soldering equipment and tools, plus electrical insulation tape.

This kit should be suitable for all three variants of QCX: original, plus, and mini. We do not own an original QCX so are unable to test it but the relevant part of the circuit is the same. To fit, simiply connect to 5B, GND, audio output, and the wiper of the audio potentiometer.

Since the AGC PCB measures just 27*8mm, the PCBs are manufactured as a panel. This means that you might want to gently file the edges where the PCBs were connected. Practically there is no need to do this as there is adequate clearance but in case you are particularly picky about a clean edge, you have been warned. Also note that the PVC wire insulation may shrink very slightly when soldered but this can easily be compensated for.

Note: paper manuals are not provided, PDF documents are available here under the 'Attachments' tab.

See also Lex PH2LB's blog suggestions here.