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#1 2009-12-18 11:34:19
- wa2mze
- Member
- From: South Florida
- Registered: 2009-08-22
- Posts: 171
new universal dds vfo
Hey DIZ,
I see in your kits section you have a new DDS VFO under development. I looked in the retired kits section and there was the AVR-DEV, which had a DDS chip in there. So my question is will your new DDS VFO be based on the AVR-DEV kit, or will you be using a newer DDS chip? I would vote for the AD9951 family as they give the most bang for the buck (14 bit DA and 400mhz clock!). Soldering those tiny chips ain't easy, but it isn't impossible with a well designed PC board and a small tip soldering iron (I've done it). As far as the cpu is concerned, the atmega324 or atmega168 family are nice with 20mhz clocks, lots of IO, and upgrade available to larger memory family devices for new features. Getting the cpu clock as high as possible helps keep cpu garbage out of the signal path (40mhz PICS start out of the SW spectrum, but the 20mhz AVR's have their clocks in a save place and the second harmonic is out of the SW spectrum).
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#2 2009-12-19 08:07:15
- W8DIZ
- Administrator
- Registered: 2008-08-12
- Posts: 317
Re: new universal dds vfo
Hi Ken,
The old DDS kit was a ARCI "buildathon" project using an AD9835. The new DDS project I am working uses an AD9834, which runs at 75 MHz
Reason for the AD9834 is that it is simple and easy to work with and relatively inexpensive.
The AD9951 is obviously a better chip but more expensive and very difficult to solder
Other people already have the AD9951 DDS kits available but they are costly. Google WA1FFL.
-Diz
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#3 2009-12-19 08:33:22
- wa2mze
- Member
- From: South Florida
- Registered: 2009-08-22
- Posts: 171
Re: new universal dds vfo
Looking forward to seeing your design on the web.
Isn't the AD9834 is the same part used in the NorCal FCC-2 kit? Not bad, but limited to about 25-30 mhz output. That will still work as a vfo for HF though you will have to resort to low side injection on the higher bands. The AD9851 is about the same difficulty to solder, but has double the clock frequency and will give output to about 75mhz. It's the one used in the DDS-60 which I've also built. I have a small DDS PC for the AS995x from I0CG that I'm still missing some SMT parts to complete. I've already got the chip soldered to the board (with some help). I wish WA1FFL would offer his PC board by itself, I'd rather use an AVR processor than the 8051 (I have software tools for the latter).
The AD9951 and the AD9851 are now both about $21 from Digikey, while the AD9834 is about $10 (they have both the bruz and cruz versions, the cruz is the 75 mhz part). I was able to get a few AD995x chips as samples awhile ago. Guess I wouldn't eliminate the faster chips due to price, they are more expensive but sill reasonable. OTHO the newer AD9910 and AD9912 chips which clock to 1ghz (!) are over $50 at Digikey.
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