Key clicks are generally undesired "clicks" or "thumps" generated by a CW transmitter as the key is put down or let up.
The sharp edges at the start and stop of the carrier include a lot of undesired frequencies that sound like clicking to those listening on adjacent frequencies.
Key click filtering is designed to smooth the edges at the start and stop of the carrier to reduce the key clicks.
Carrier with no filtering: | ![]() |
Key clicks: | ![]() |
Carrier after filtering: | ![]() |
Simple filter circuit: | ![]() |
- When a carrier is interrupted, as in CW, a sharp interruption will cause sidebands which manifest as Key Clicks. These can cause interference over a long distance and wide band of frequencies
- Additionally, depending on Tx design, there may be a small spark as the key or keying relay operates which can cause localised interference
- The rise time should be conditioned with a key click filter