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Old May 29th 05, 09:48 PM
Harold E. Johnson
 
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Would that be the DDS controled receiver design from the UK?
His DDS-Micro design was in an ap-note on the Analog Devices
web site (pdf download), but source code wasn't published.
The specific pic micro he used is now obsolete, though similar chips
are available (require software changes). Also the AD9850 dds
chip he used is now somewhat long in the tooth.


The very one. Source code available on the Picastar website.

I am considering building a DDS vfo for a homebrew xcvr, but
I am looking at using one of the AD9951 series chips. These clock
to 400mhz and have a 14bit D/A vs the 10bit in the 9850. Spurs
and phase noise should be quite a bit lower with the 9951 series
chips over the 9850. You will need a surface mount to .1 mill
spacing proto board to hand solder it (not to mention good eyes
and/or a strong magnifier, and steady hands). Such proto boards
are available on ebay sometimes, and can also be found for sale
via a google search.


I've been running a 9951 overclocked at 600 MHz (It'll do a bit over 700
before it REALLY doesn't like it) Waterproofed in the shielding department,
feedthru decoupled and on a 2 layer board with PTH copied from the AD proto
board. BTW, the 9951 is still running cool at 600 MHz (External LO) with the
center post solder grounded to a large PTH.

Seven pole band pass filter, also in the DDS box. Phase noise is
non-existent. Spurious, while at the AD specs is still objectionable.

W4ZCB


 
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