Improving the CW wave shape on TX

Allan VK2GR was concerned to reduce key clicks and improve the shape of CW from the µBITx.

Being mainly a CW operator, he was concerned about the V3 board uBitx transmit CW wave shape being very hard – almost a square waveshape. As expected, key clicks could be heard on either side of the signal. A look at the circuit diagram and a little tinkering has vastly improved the situation.

The photo above shows where a short wire was soldered to the hot side of C1 for the tests. In reality the wave shape is now a little soft on the trailing edge, so 0.047 or 0.68uf may be sufficient for some people. More work could possibly be done with the CW keying RC network to the 1st balanced mixer, however this one component simple fix will suit my needs.

All that was required was to increase the value of C1 from 0.1uf to 1uf. Below are some oscilloscope photos showing the end result of improvements to the leading and trailing edge of the transmitter output using a 1uf connected across C1.

Reference

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