Using the CAT interface of the QCX it was already possible to retrieve it’s frequency in N1MM. I made great use of this function during the Region 1 CW Fieldday last June. What would make it even better was the ability to key the QCX from within N1MM just as I with the Icom IC-7300. In N1MM you can choose to do CW over DTR. Although the QCX will not accept DTR over it’s CAT interface, we can overcome this by building a small circuit with an optocoupler and connect it to the (straight)key input.

A few weeks ago I stumbled on this solution, given by Guiseppe IU8EUN, in a post on the QRPLabs forum. Unfortunately, due to space issues of the group, the images of the schematics were deleted. Luckly Guiseppe was so kind to send them by email. Thanks Guiseppe! A quick test setup taught me that this schematic does exactly what I was looking for, only, such a breadboard setup is rather messy and impractical. So I decided to make another PCB.

QCX CAT & Key Interface Schematic

Starting from the schematic above, and ending with the PCB below.

QCX CAT & Key Interface Board

I have to admit the board looks rather big for the number of components that are on it. The space on the left it to fit a USB to TLL dongle, and the holes are to strap it in place with tyraps.

2 Replies to “QRP Labs QCX – CAT & Key Interface Design”

  • Hi, I’m looking for a cable to connect the CAT of my QCX-mini to my computer for using N1MM. Should I buy a 3v3 or a 5v? Which of these 3 cables would fit?

    Letotech TTL to USB Serial Converter USB TTL-232R-5V-AJ 3.5mm Audio Jack UART Adapter Cable,6FT

    Jxeit FTDI TTL-232R-3V3-AJ Cable with Audio Jack Connector with 3.3v Based TX and RX Signaling, USB to AJ 3.5mm TTL Serial Cable

    DTech 6ft FTDI USB TTL to 3.5mm 5V Adapter Cable FT232RL Chip Audio Jack TX RX Signal Windows 11 10 8 7 XP Vista Linux Mac (6 Feet, Black)

    I would appreciate your help!

    Mary VE3INE

  • Hi Mary,

    You’ll need a 3v3 cable, a cable with TTL Level serial data. NOT RS232 which is a different (higher) voltage.

    73 de ON5IA

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