Re: DDS spurs


From: Leon Heller (
Date: Sat Sep 28 2002 - 13:19:25 CDT

>From: "Matthew Balmer" <>
>To: "Low Power Amateur Radio Discussion" <qrp-l@Lehigh.EDU>
>Subject: DDS spurs
>Date: Sat, 28 Sep 2002 17:32:30 +0100
>This is a second attempt at sending this so apologies if it doubles.
>I am interested in experimenting with DDS operating at 14 and 22MHz,
>via a PIC. Spurs seem to be a problem with DDS VFOs, most sources I've
>seem to suggest around -50dBc for the spurs.
>Just how much of a problem are these going to be to a high performance
>receiver? It is obviously going to be a problem with the spurs mixing with
>other signals, and clearly the problem it will cause will depend on the
>strength of the signal it mixes with.
>I know I could use a "clean-up" PLL but I'm interested, if it won't harm
>performance too much, in just using a simple DDS VFO.
>Any comments/experiences would be greatly appreciated.

ADI has some software for the AD9850 that tells you where the spurs are. I
forget what it's called, but I've got a copy somewhere. You could use it to
adjust things so that you don't have too many in the bands you are using.

73, Leon

Leon Heller, G1HSM Tel: +44 1424 14790
My web page:
My low-cost Altera Flex design kit:

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