Re: DSB transceiver for Digital mode
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This is a bit history for D4D: A simple QRP transceiver kit for FT8.
D4D stands for DSB transceiver for Digital modes. It is a Double Sided Band transceiver kit designed for digital modes, especially for FT8. If you have chance to try FT8, you will be amazed by the strong decoding capability due to the communication protocol, digital signal processing and software. I still remember clearly a YouTube video by W6LG who communicated with a bulb. I started to think how much the transceiver could be simplified if you have a moderate antenna like a full sized dipole or EFHW instead of a bulb. A DSB transceiver is much simpler than a SSB transceiver, however it was never used for FT8 as far as I know. I did some experiments on my Choc perf board, a specially designed perf board for RF circuit experiments. I started with a direct conversion receiver for FT8 and it worked okay. Then I built a DSB transmitter and the transmitted signal can be decoded. By referring to the DSB designs of AA7EE, VK3YE and ZL2BMI, I combined them using only one NE602 and a PTT switch and it gave me success to make a few FT8 QSO’s. Personally I really enjoyed it because a manual PTT switch will save power consumption and circuit complexity, but you will need to well sync with computer, although it was not really a problem for me. Per request from a few hams, I found a VOX control circuit and modify the hold time to be compatible with FT8, and I put them together and made a few improvements on the signal purity and frequency stability, and it finally became our D4D. Do we have to worry about the unwanted Lower Side Band? Maybe, but for a transmitter of 1-watt, it is not really a big problem. Is it just a toy for a transmitter of 1-watt and only half of the power will be effective? Not really, as I can easily make a few QSO’s as far as 1500 miles range for 40-meter band.