Hi Janne, To avoid the spurs from DDS altogether it may be easier to use a PLL/VCO instead. I was planning to build a 400-900 MHz PLL to drive the SDR hardware but I don't have time to do it. Freq resolution of this PLL doesn't need to be high since Winrad can cover a 48-192KHz window. PLL step size can be in the range of 200KHz. It may be easier to build than the DDS. Minicircuit Labs' POS-900W VCO will be a good choice for this. I am not sure whether you can find a 7474 type of flipflop fast enough to cover the freq range you need as it need to be able to divide >200MHz clock. 73 de DJ/NM3R
----- Original Message ---- From: iami78 <[EMAIL PROTECTED]> To: [email protected] Sent: Wednesday, March 14, 2007 8:27:59 AM Subject: [soft_radio] Re: Single AD9954 with counter or dual AD9954 to form IQ VFO. --- In [EMAIL PROTECTED] ups.com, "D. J. Wang" <[EMAIL PROTECTED] > wrote: > >Hi Janne, >I have built two boards, one with AD9951 and another with AD9954, >since they have the same pinouts, I used an identical PCB design. The >most difficult part is line up all 48 pins and solder them, there >wasn't that many external parts to solder after that. >I agree that using the internal multiplier is not a good idea as it >generates a lot of spurious signals but I was just trying to get it >working as quickly as I can. DL5MGD published the PIC hex code and a >VB prgram so you can control it with an 16F877 or thru printer port. >That make thing a lot easier. I would have to rewrite it if I change >the reference clock frequecy and multiplication factor. Later, I did >write some AD9951 control code when I get more familiar with teh DDS >chips and modify IW3HEV's VNA program to drive my AD9954, it turns >out it was not as difficult as I original thought. >DL5MGD's design is pretty good and you certainly can improve the >spurs by using an external 500-550 MHZ clock. I0CG's design uses a >XTAL OSC at 100 MHz or so and filter out unwanted harmonis. Spur >improvement probably depends on how clean the 100MHz osc you will be >using. > >73 de DJ/NM3R Hi D.J.! I'm pretty sure that this whole DDS language will become really clear after you once dive into it - just like you mentioned. Too bad that we don't have any DDS experimenters at our club or even on the bands. Seems like DDS is still a little bit underground among ham radio operators. Anyways, I started to draw the circuit board, and yes, it has two AD9954. I'm gonna do the hardware and then dive into the software thing. What I can't really figure out is, how do I sent the commands to the DDS chip. If I want to for example just change the frequency, do I sent FTW0(xxx) in ascii format. Because the DDS chip isn't cpu, I think that you first send the register number and after that the value? As you may notice, I don't have the slightest idea. 73 de Janne, OH1GTF ____________________________________________________________________________________ Expecting? Get great news right away with email Auto-Check. Try the Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/newmail_tools.html [Non-text portions of this message have been removed]
