Home |
Search |
Today's Posts |
#1
|
|||
|
|||
QUESTION: Spectrally pure DDS Output?
I have the following question regarding DDS chips:
The amqrp website and others detail techniques for using Analog Devices', DDS chip as an accurate digitally controller oscillator. One of the issues that needs to be bourne in mind according to the articles is the spectral purity of this chip's output. There seem to be various schemes using PLL and filtering to kill the harmonics and spectral "grass" that these things seem to generate. Given the onward march of technology, is there any chip similar to the Analog Devices DDS, that would give be a spectrally pure, low noise sinusoid with any further filtering or PLL? I'd like something good enough to be a high quality VFO for an HF receiver (I and Q available)?? Is such a thing available, preferably offering a presoldered evaluation board (I don't want to go blind soldering it!!) for 30 or 40 bucks kind of price range?? Thanks, Tim |
#2
|
|||
|
|||
Wellll... I know a company that sell a DDS-based LO VME module with
very low spurious, but the price isn't "30 or 40 bucks." More like 500 times that. They are pretty tight-lipped about just how they do it. Cheers, Tom |
#3
|
|||
|
|||
A DDS chip on its own may cost more than 30...40 dollars, unless the
manufacturer is willing to send you a sample. And what is wrong with AD 995X series DDS? They are of a very low "spectral grass". You can also get an idea for how much AD sells their DDS evaluation boards by browsing their product catalog. wrote in message oups.com... I have the following question regarding DDS chips: The amqrp website and others detail techniques for using Analog Devices', DDS chip as an accurate digitally controller oscillator. One of the issues that needs to be bourne in mind according to the articles is the spectral purity of this chip's output. There seem to be various schemes using PLL and filtering to kill the harmonics and spectral "grass" that these things seem to generate. Given the onward march of technology, is there any chip similar to the Analog Devices DDS, that would give be a spectrally pure, low noise sinusoid with any further filtering or PLL? I'd like something good enough to be a high quality VFO for an HF receiver (I and Q available)?? Is such a thing available, preferably offering a presoldered evaluation board (I don't want to go blind soldering it!!) for 30 or 40 bucks kind of price range?? Thanks, Tim |
#4
|
|||
|
|||
I think you'll have to say what is acceptable to you and define what you
mean by "spectral grass". In terms of phase noise, you'll do better with a normally designed DDS than you will with a normally defined PLL. For data on what a DDS can do rephase noise, look at various models of synthesizers on the PTS web site. Now of course there are spurs to contend with in any DDS design, but discrete spurs are not what I would call "spectral grass". If spurs are indeed your issue, you can go to a 14 bit DDS (AD9951 or others) and get at least spurs at least 80 db down, or add filtering to the DDS output. Chuck |
#5
|
|||
|
|||
|
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
The FAQ (Well, Question 1, at least) | Homebrew | |||
The FAQ (Well, Question 1, at least) | General | |||
Yagi / Beam antenna theory question... | Antenna | |||
Grounding question - this is wierd..... | Antenna | |||
Question regarding police tactics and scanners | Scanner |