That's what I'm calling it anyway. It's not really a CW key, and it's intended use is more so for testing through the generation of the CW carrier. What you will see in the picture, is a very simple device that plugs into the 3.5mm KEY socket on most CW capable transmitters (or the 1/4" socket with a converter). It consists of a simple IP65 button that can be used as a CW key and a toggle switch to have a constant CW carrier – great for testing.
You probably wouldn't use this for serious CW has the button action is pretty heavy so I'd imagine some RSI would result. However, for a quick test I think it'd be great.
It's real use though is for testing and tuning. That being, if I need to tune up my radio, rather than using AM I can send a nice and narrow low power CW signal and tune up. Or for testing, if I need an RF signal I can simply tune my radio to the frequency of interest and then flick the toggle switch for a continuous RF signal.
What led me to build this now, is that the 'DATA' port on my FT-817 seems to no longer be accepting 'Data In' – as in the audio. So although my digital interface can still trigger the PTT via the DATA port, the audio I send no longer seems to be received and thereby no SSB generated. (Testing on my digital interface seems to show it's working perfectly, and I can still transmit voice SSB with the FT-817.)
This is inconvenient as it happened while I was testing my 2200m transverter. You see, I was using fldigi to generate a tone via my digital interface into my FT-817 so that I could have an RF source to easily test with. But after stopping one test and going to start another, I noticed it no longer worked.
But now, with my little 'CW Test Key' I can easily generate an exact RF signal and I can do it without the need of a computer and digital interface. However, going forward I'm going to struggle to do things like WSPR and PSK31 on 2200m. I will need to modify my digital interface to use the Mic socket instead it seams.