Software and operating instructions

I'm assuming you've read my article describing the Arduino controlled DDS-60.

Click here to download the Arduino software. It now has a "Transceiver mode" which is selected between normal mode and QRSS when pressing button 1.  You'll know when it's in transceiver mode because RX will appear in the top right corner of the display.

Transceiver mode implements the transmit / receive switching, audio sidetone, frequency shift and RIT (receive incremental tuning).

The two settings that you might want to change are:

CW_FREQ. This is the CW audio frequency in Hz. I like it to be about 800 Hz but it's a personal preference. This sets both the audio sidetone and, more importantly, the DDS frequency shift that occurs between transmit and receive.

TR_TIMEOUT. This is the transmit / receive timeout in ms. i.e, how long the key has to be up before we switch back to receive. The best value depends on your sending speed but I've found that 750 ms works well for me.

At first I wondered if I might need to use interrupt processing for the CW signal but this wasn't required. Polling in the main loop is easily fast enough. The loop executes in microseconds when the tuning encoder is not being turned.

Operating Instructions

Set to transceiver mode by pressing button 1.

On receive, the DDS frequency is CW_FREQ (e.g, 800 Hz) higher than what the display shows. Therefore, if you tune to the high side of a received CW signal so that the audio tone is CW_FREQ then the display will show the transmitted frequency. It is important that you tune to the high side if you intend to reply to the station, i.e, if you can turn the tuning knob so that the displayed frequency increases and the pitch of the received CW audio gets higher then you're on the correct side. I chose this side because it kind of feels more natural to me and it's the same side that you would use to resolve LSB phone signals further up the 40 meter band. Be careful at the band edges. You could end up transmitting outside the band if you tune to the wrong side.

On transmit, the DDS frequency and therefore your transmit frequency is exactly what is shown on the display.

Button 2 toggles the RIT on and off. The offset in Hz appears in the lower left of the display. The frequency step for the RIT is selected with button 3 in the usual way but the value is maintained separately for the RIT and the main tuning. Changing one won't change the other. I prefer to have the RIT at 10 Hz per step while the main tuning is usually at 100 Hz or higher.

That's about it. There are room for improvements as I will talk about later.