Re: [soft_radio] Re: DDS + PLL to clean up spurs?

[Nick Whyborn]

Yes, its called dither. Its possible to add dither independently to the phase accumulator output and the sine LUT output. Don't think Analog Devices use it, Xilinx have it as an option in one of their FPGA modules. There is also a US patent 5,291,428 on it by a certain D. Talbot (!). Nick G4JNX. Andy wrote: Yes, definitely.   This really came home to me when I directly multiplied the output of an AD9852 DDS at 72MHz up to 10GHz, then listened to it on an SSB receiver.   It sounded absolutely disgusting - like a ball of noise several tens or even 100s of kHz wide. I could only just about discern the carrier at the centre frequency.   All those millions of close in spurii at -80dB, when passed though a times144 multiplier, intermodulated and in-bred massively.   Simple theory says they should have increased by 20.LOG(144) = 43dB, but seemed worse than that even.  Hence the crystall oscillator PLL approach described last time, quickly put together when I'd recovered from the horror of the direct multiplication result :-) The deliberately added noise sounds a fascinating idea - do you know if Analog Devices (or anyone else) do, or intend doing, something like this in any of their products? Andy  G4JNT www.scrbg.org/g4jnt/ SPONSORED LINKS Ham radio Craft hobby Hobby and craft supply Icom ham radio Yaesu ham radio YAHOO! GROUPS LINKS  Visit your group "soft_radio" on the web.    To unsubscribe from this group, send an email to:  [EMAIL PROTECTED]    Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.