Description: Also look at QEX Feb. 96. You need to look at the QEX 12/98 article to understand this circuit.
Description: This is a partially Synthesized VFO intended for use with equipment with single conversion near 9 MHz. The VFO will cover 3.5 to 30 MHz continuously.
QEX JULY 97
Description: The is a direct digital VFO that will tune from 100KHz to 20 MHz using the Analog Devices AD9850 IC. The Tuning is done with a GH6102-ND from a Digi-Key rotary Shaft encoder that drives a PIC16C54 uP. The uP code is available on the ARRL bulletin board. The frequency is displayed on a 16 character by 1 line liquid crystal display, DigiKey # 73-1016-nd. Major parts required are a rotary shaft encoder, a PIC16C54 uP, AD9850 IC and a liquid crystal display. Data sheet available at www.microchip.com.
Replaces ment LCD, about any single line by 6 to 10 chartacters LCD will work - most are standard pinouts on the 16-in connector. You can get one from Digi-Key (p/n 67-1778-ND).George N2APB can sell one for $7 via PayPal to email@example.com. Two other replace ment LCD are 153-1090-nd is the Digikey part number for the LCD display with backlighting or 153-1080-nd without backlight.these are 8 digits instead of 6.Since the PIC resets the display after each cycle, the two most significant digits will never get displayed.
An updated version (Ver 4) is available. This is the board with the changes described by AA0ED and AA0ZZ at their web site www.qsl.net/yo5ofh/projects/dds_vfo_by_n2apb/dds_vfo.htm There is also a 78L05 regulator added to the board.
Look at http://www.page.sannet.ne.jp/kenjia/vfo.html about a program for Windows that will display everything for the project.
Check the ARRL QEX web site for technical updates.
Programmed PIC16F84 for the version 4 DDS code for 100Mhz operation is available.
Bill (WA3JTX) writes: I built the synthesizer on your PC Board, and it worked first time I turned it on! I used a 16F84 PIC and modified the synthesizer code to produce a frequency range from 10 Hz to 30 MHz! Intermods/noise/harmonics were down minimum of 58 dBc, and in close spurs were down about 65 dbc. The noise floor was down greater than 85 dBc, the limit of spectrum analyzer. I obtained the Synthesizer chip as a sample from Analog Devices.
From W0OFF: "I just received the board from you today, and also my parts order for it from Digikey. This sixty-one year old guy had a lot of fun soldering the surface mount components by hand, but it all went together in a couple of hours. It worked just fine the first ime.
Description: This is the VFO for the Tuna Tin transmitter that also was in QRPp, (look under the transmitter paragraph). The project uses two MPF102 FETs for a VFO that tunes the lower end of 40 Meters.
Description: This project consists of three pc boards, two on 2.55 ER .030 teflon and the power supply board on FR-4. The mini kit consist of the three boards, the chip parts that mount on the two teflon boards (the chip fixed resistors, a chip capacitor, SM schottky diode). Note: the power supply board is not shown in the article.
Description: This project allows the R4 receiver to tune a 0.5 MHZ frequency range from 1.5 to 30 Mhz with an LCD display. The mini kit consists of the programmed PIC, PC Board, (2) 7805 regulators, the MC145170d2 IC, op27gz opamp IC, and Mini Circuit 100 mhz VCO. The mini kit includes all the hard to get parts. Please specify the R-4 OR SPR-4.. See www.arrl.org/files/sqtbinaries/drake_synth_zip