Jumat, 22 Juli 2011

DDS AD9851

DDS AD9851 for the HF + 6M Transceiver Radio

Direct Digital Synthesis (DDS) is a frequency generator with digital synthesis using a reference clock. The principle is no different from the PLL (phase locked loop), only the PLL uses a VCO to generate the frekewensi. In other words DDS = digital PLL.
DDS has been widely applied to radio transceiver, especially at the low end segment of the factory transceiver. Medium segment of mid and high end, still using the PLL, with consideration, for now the PLL is still better than DDS.
DDS uses firmware homebrew made by CV.Niras (VU3CNS) with some modifications on the hardware. In this project I use the AD9851. AD9850 can also be used, but the 6x multiplier it should be disabled, and use max 120MHz reference clock.

1. Using the AD9851 and 2x 16F628A
2. 25MHz reference clock, 6x multiplier
3. Generating frequency from 0-60Mhz
4. Having VFO-A, VFO-B, and RIT
5. 20 programs have memory to store the VFO-A and VFO-B
6. Mode control has a LSB, USB, CW, and AM
7. Having control for BPF and LPF for the entire nine HF bands (160m, 80m, ...., 10m)
8. Input data using a mechanical encoder and numeric pad.
9. Has 6 control buttons Save / Memory, Split / VFO A = B / RIT, Lock / Mode, Step, and Calibration
10. RF output is around 20mW (MAV-11)
11. Display frequency: direct, LO-IF, or IF-LO.

Aside from being a Local oscillator in radio communications, DDS is also used as signal generators, function generators, etc..
DDS IC soldering into the PCB requires precision and patience are very high. It is small and the distance between the feet is very tight. I failed 3 times already, which means I lost 3 pieces of PCB and 3 IC DDS, mahaaal experience.
To make it easier for soldering, and assemble his DDS IC, I bought a 28 pin SOIC to DIL adapter PCB (U.S. $ 2 + ongkir), and re-designing its layout pcb with 28 pin DIL.
Since the AD9851 output signal is only 0.5mW, and I plug 60Mhz LPF and MAV-11 amplifier. Signal is strong enough, and enough to drive the diode mixer level 7 or 10.

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