Like a lot of hams, [Stuart] wanted an “on the air” sign. These signs often connect to a PTT switch or maybe an output from the transmitter that also does things like switches antennas or switches in an amplifier. [Stuart’s] version, though, simply senses the radio frequency emissions from the transmitter and lights up that way. You can see two videos about the sign, below.

Honestly, we are a little worried that he might have too much RF at his operating position. Presumably, the device is pretty sensitive, especially if there’s any actual antenna on the sign. A comparator and a pot let you set the sensitivity so it doesn’t light up when your garage door opens.

The sign itself looks great thanks to a laser cutter. LEDs light up the entire sign in either red for on the air or another color for receiving operations. The acrylic sign is edge-lit which gives it a very nice effect.

We always enjoy edge-lit projects. Reasonably simple to do, and the effect looks great. If you have a laser cutter, you can get some very professional-looking results. If you are interested in the FT8 communication mode, we’ve talked about it before.