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K2 USB interface

This page was last updated : 06-Jun-23 14:51:02

This page is work in progress and will be updated frequently (last update 6 jun 2023). 

End July 2022  I got my hands on a used Elecarft K2 with a few options : 

• KAF-2 - Audio filter and realtime clock
• KAT-2 - Internal antenna tuner (with 2 antenna inputs)
• KNB-2 - Noise blanker
• KSB-2 - SSB unit
• DIY PTT output

And although it needed some work (for example : the 20m band needs alignment, undocumented MODS), I'm quite happy with this QRP rig.

Because the  Elecraft K2 is a modular transceiver, it has even more room to add even more modules like :

• KIO-2 - RS-232C interface and AUX I/O
• K160M 160M and 2nd RX Port
• K60XV - 60m + Transverter Adapter Kit 
• KBT2 Battery

All these options lave a lot of large holes in the back. And one which got my eye was the AUX IO place for the KIO-2.

FTDI USB to TTL Serial Adapter

Because I work a lot with embedded devices I had a  stack of FTDI USB to TTL Serial adapters (link) laying around. I use these FTDI based adapters because most OS's have build in support for this chip, are stable and are well documented.
 

Looking at the schematic of the Elecraft KIO2 (link) it shows that the K2 exposes the TLL serial signals on header P4 on the Control Board.

 

So the little USB/Serial adaptor could be used to control my K2 with my computer. 

 

Connecting FTDI to Controlboard aka cable assembly

The connection between the Controlboard (header P4) of the K2 and the FTDI adapter isn't 1:1 so you need to have make a custom cable.

The connections are : 

• P4-1 (TX) to FTDI RX
• P4-3 (RX) to FTDI TX
• P4-5 (GND) to FTDI GND & CTS

A schematic of the wiring is shown below. 

I used a shielded cable for the RFI and connected the shielding to the GND of the FTDI adapter. A little shrink tube was used to tiden it all up.  

My cable has the following colors :  

• White = Control board TXO - FTDI RXI
• Red = Control bard RXI - FTDI TXO
• Black = Control board GND - FTDI GND & CTS

Holding the PCB.

Using Tinkercad I 3D designed a holder for this adapter which fits in to AUX-IO hole.

 

 And after a few iterations and minor changes, it all worked out.  

The assembly exists of 2 parts : 1 to expose the PCB to the outer world (left), and 1 to fixate the PCB (right)

The adapter PCB is placed into the first part.

And it's fixated by placing the second part. 

And it looks good as I may say so. 

It even fits perfect, except for the long screws (I went into town and bought a bag of M3x16 RVS).

And once installed I decided that I need a re-design of the lock part. Now it has room to insert the M3 nuts. 

 

Everything into place

Testing

As stated the Elecraft uses the following settings (I used FLRIG for testing).

And it all worked out.

Next stop is finishing my K2 digimodule so I can use it with other digital model applications like FLDigi & WSJTX.

 

 

Important notes  

1. As Mike, K8CN correctly pointed out in this groups.io message thread, in addition to the serial interface, the KIO2 includes an AuxBus output and +12 VDC for use with small external accessories, as well as signals for controlling an external power amplifier. This mod only provides a USB/Serial link between the K2 and a computer, not implements the additional signals like RF, ALC, 12V and the 8V when receiving. When you just want to control your K2 with a computer, this mod works out. 
2. I have tested it only with my basic (QRP) version of the K2, no QRO amps etc. So it might be that this mod doesn't work well when you use high power. 
3. There are also fake FTDI chips out there (ilegal clones) which may work for now, but after a OS update may start to fail (FTDI is using a deny list in there drivers).

 

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