The KX3 radio is great for field work, but unfortunately problems can arise with stationary work. Despite a large number of connectors, it lacks those that are standard in stationary transceivers.
If you want to use the KX3 (almost) like a stationary radio, you have to do a bit of tinkering. The box on top photo is the "PTT box with antenna switch". Big Jack - signed as 6 - is a connector for the footswitch, to this connector I can also connect the cable from the third picture - PTT using COM port (for example for fldigi). Later I will use third cable for VOX audio. On the picture below you can see that cable 2 is connected to the radio - this is the KXUSB cable enabling the use of CAT. CAT enables also PTT, but this is not the PTT I want. The whole problem is that I have a receive antenna switch in box 8 and I have to switch the antenna to the transmit antenna before turning on the PTT on the radio. So you could say that the "antenna switch PTT box" is a primitive sequencer. I turn on PTT, the box switches antennas, and "pushes" PTT in the radio. When you release PTT (either using footswitch or on the COM port), it does the opposite - you turn PTT off in the radio and switch antennas. Additionally a +12V signal will be available at the external socket when the PTT is pressed. This is all so that you can, for example, turn on the attenuator at the Web SDR input - to not to hurt it while transmitting.
As you can see, the whole thing is mounted in printer data switch housings from the old days. They are perfect for such purposes, because they usually have the same, or very similar dimensions and are made of thick steel - great shielding! :)
- power supply
- USB connection to PC
- PTT input from PTT antenna switch
- audio splitter - for connection to PC and to headphones / speakers
- Input from the computer's sound card (It would be good if the input and output were isolated, although this is not absolutely necessary for QRP - you have to set the levels carefully. In the radio, set the equalizer to 0, turn off compression, set the microphone gain to half, set the audio level from the computer so that the ALC is between 5 and 6 bars - this will ensure a clear signal on FT8, RTTY or whatever you choose)
Such a kit like this greatly extends the capabilities of any portable QRP transceiver. It may not be a perfect solution, but two boxes like this make it easy to use additional receive antennas, PA control, etc. This is a compromise solution for those who can't afford to have a stationary radio that "has it all".
In some future post I will describe in more detail how these boxes are built.
English 
Polish