Tom WB6B wanted to build a new filter for use with the uBITX (to overcome harmonics on his output). However, he didn’t want to build a filter that would be strictly tied to the uBITX.
So he built a standalone Low Pass Filter box that works as an add on filter for the uBITX as well as becoming a general purpose piece of Ham equipment he can use over and over for other needs.
It uses an arduino to measure the frequency you’re transmitting on and select any individual or combination of filters you like. The proposed design uses a set of filters and a relay switch board; such as to ones by QRP Labs. But, the Sketch code should be easy enough to modify for whatever you like.
The controller can show the selected filter with LEDs. Alternatively it can be configured to use an LCD display, which will display the transmit frequency as well.
Tom’s unit is still under construction, but he has built and tested a prototype with a signal generator.
He is releasing the preliminary design now because it is complete enough for people to try out on their own filter designs. It makes using outboard filters really easy, and he thinks people will like it.
Tom welcomes feedback on improvements people make while building their own “Auto Filters” with the controller.
The code for the controller is here: https://github.com/mountaintom/TX_Auto_Filter