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哈!楼主误导广大爱好者.ad9850/9851 不可能直接工作在两米波段,可以用其控制一个pll,或用ad9852 ad9854直接产生.没有dds 芯片部分就不能称其为dds. [表情]
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呵呵，如果真的“误导”了广大爱好者，我在此向大家说抱歉，本人是纯外行，请见谅，只是我对这个电路感兴趣，也正在做实验，想验证一下是否真的可以用在vhf段，想和大家分享一下而已。
如果真的觉得是误导大家，请版主把此帖删掉吧，sorry!! 下面把原作者的部分文章贴出来：
the original dds pc board design through to the current boards are compatable with the original software from the njqrp groups website. this means that all pin functions on the pic16f84 micro have been kept the same. the software allows the dds to be used anywhere between 0 & 30mhz, & had bandswitching to jump between the various hf amateur bands. it also allows the dds to be used as a signal generator, or a local oscillator for direct conversion receiver, or transmitters. the software does not allow for display offset to dds frequency for intermediate frequency type transmitters or receivers. the original software although very good, was designed to use a optical type rotary encoder for tuning. these are very expensive in australia > $100 aus. the mechanical types were tried & do work, but can cause the dds to jump large frequencys due to contact bounce.
i was looking for software that would allow the dds output frequency to lcd display frequency offsets, & if frequency offsets to be able to be programmed to make it more useable for building equipment for the vhf to microwave bands. i was also looking at designing a basic ssb/cw transceiver for 144mhz similar to a ft290r. the new software required the following functions.
1. use the original pcb, modified to gain access to ra2..ra4 pins.
using diodes to provide the number of switch inputs required;
2. dds frequency output, 0hz to 40mhz;
3. tx/rx switching. by grounding ra4 to go to tx mode;
4. frequency readout can be offset by 1hz to 11ghz;
5. no requirement for band switching, but able to program upper and lower
limits;
6. memorise the last frequency on power up;
7. use low cost mechanical rotary encoder instead of the optical type;
8. variable rate tuning not required;
9. by grounding ra2, (pic pin 1) then turning the rotary encoder, be able to
set the step size required. eg 100hz, 1khz, 10khz etc;
10. use 16x2 lcd with or without r/w pin. (use delays rather than busy
checks);
11. software fine tuning of the xtal oscillator frequency still required;
12. rit available in rx mode by grounding, via diodes, both ra3 & ra4;
13. still require the option of programming the software for different xtal
oscillators. eg 66mhz, 100mhz, 125mhz
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further information on programming the setup screen using the calibrate button when powering up can be read in the synth.asm file. for quicker programming of the dds software the synth.dat file can be modified to suit your application.
thanks goes to steven jones for re-writing the new software. the software includes the synth.asm, synth.dat, & synth.hex files. it is being supplied free for all amateurs.
a/b, & gnd. the older type eme85a board will need modifying to add an extra diode to the ra4 connection on the 16f84.
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example showing the software programmed for the 144mhz band.
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