The N4YG DDS system was originally designed for the HW-101, whose VFO drifted badly and tuned erratically. The DDS project was very successful and made the HW-101 a winner. It compares very favorably to the most expensive rigs out there in terms of stability and convenience of operation. Over a period of about 6 years, it became evident that the same hardware and most of the firmware associated with the system was directly applicable to other old radios which used analog VFOs and PTOs. The system is particularly applicable to transceivers which have digital frequency readout, making the installation into the transceiver much simpler and requiring less modification to the radio internally and no modification at all externally. Ten Tec transceivers with PTOs and the Drake TR7 (also the RV7) are good examples. The frequency range of all these transceivers is 5.000 to 5.500 MHz, although they need not be the same.
The system consists of a PC board measuring 3 inches by 3 inches, an incremental encoder to which the main tuning knob is attached for tuning and interconnecting cables which provide the interface between the PC board and the transceiver. Additional components are required for the Heathkit SB and HW series of gear. These are a liguid crystal display (LCD), a band sensor. a potentiomenter for receiver incremental tuning (RIT) and a pushbutton switch. Unlike many DDS boards which have only a few millivolts of RF output, the N4YG DDS board has an integral output amplifier with adjustable output up to 20 volts peak-to-peak, which is sufficient drive for almost any application. The board accepts either 12.6 VAC or 8 to 12 VDC to power the system.
For additional information on the N4YG DDS system and your particular application, click on one of the links below.
The Corsair II is an example of a great rig with a poor CW sidetone. A nice sounding sidetone requires a good sine wave and proper shaping of the leading and trailing edges of the keyed waveform. While analog techniques can provide a good sidetone, direct digital synthesis(DDS) has been found to provide a superior sound. That's right, DDS applied to audio frequencies. While it may seem difficult and overkill for audio applications, the implementation at audio frequencies is much simpler than with RF. The only active component (other than a 5 volt regulator), is a single 18-pin 16F88. The hardware is not only simple but inexpensive, yet it provides a predictable, repeatable and stable sidetone. The frequency determining components normally seen in analog sidetone circuits are absent in the DDS circuit. The internal 8 MHz oscillator in the 16F88 provides the timing for the entire operation. The leading and trailing edges are digitally shaped so that popping and thumping is eliminated to the extent not possible in analog circuits. The entire circuit is contained on a PC board measuring 1.2 by 3.0 inches. It is specifically designed for older Ten Tec rigs and interfaces with the audio and keying circuits with 4 connections through which the board receives power and keying and output the sidetone to the audio amplifier in the transceiver. Output level and tone are adjustable with trim pots on the board.
The printed circuit board has been designed so that it can also be used as a Code Practice Oscillator. An audio amplifier is provided which gives ample sound even for demonstrations. Some components positions are left unfilled in either the sidetone or code practice application with only the components required installed.
Click on the image above for more information.