DOS Dream VFO
Yesf you can build your own synthesizer!
by Steven Weber KD1JV
Ai last, here it is. The VFO QRPers and home-brewers have been dreaming of—a compact, standalone, Direct Digital Frequency Synthesizer VFO with LCD readout and push-buuon operation (see Photo A). Finally, your QRP hl! with the frequency accuracy, stability, and features of your "BIG RIG." Before you wake up. lake a look at these features: • 0.0 to 25.000,000 MHz operation using Analog Devices' new AD7008 DDS chip
■ Thirty character (16 x 2) liquid crystal display, back lighted
* Push-button control
* Preprogrammed QRP frequencies for 80,40. 30, and 20 M
► Ten user memories (stored in EEPROM)
* A/B MEMO memory
* Programmable receiver local oscillator with RIT
* Ten- to 30-WPM paddle keyer (2-wpm increments)
* Decodes and displays your outgoing
Morse code • FSK keying mode possible Compact (4" X 4" X T module)
It will only take a few minutes to learn how to use all the functions of this unit Most operations involve pushing onh one button. Storing oi recalling a user memory takes iwo buttons. DFE (Direct Frequency Fntr>) takes up to 10 pushes of the buttons.
An offset frequency can be prIngram mcd to be used as a receiver local oscillator or for FSK keying. This offset is automatically added (or subtracted if the result is over 25 MM/} to the currently displayed (operating) frequency while in the receive mode (T/R line high). : [ie offset can be any frequency up to 25 MHz. With the T/R line low, the output lrequenc) is that which is displayed on the LCD.
For \ SK operation, program the offset to the frequency shift needed. The T/R line is used to shift the output frequency. Since I he offset is normal iy added to ihc transmit frequency, a high on the T/R input is the high frequency and a low is the low frequency. The FSK keying rate is limited only by the switching speed of the oploisolator. In this mode, the unit can onh be used as an exciter.
The Paddle works automatically. As you start to key. the frequency output of the sjnthesizer shifts from receive to transmit and then keys your transmitter. The Morse you key in will be decoded and displayed in the first eight places on
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