[time-nuts] Adjusting HP 5065A frequency

[Bob Camp]

Hi

If you have a divide that's "inside" the range of the DAC, there are no
nasty spurs (just DAC spurs). Once you are outside that range, there's a
stepped triangle wave modulating the carrier. You get all the sidebands that
you would expect from that very low frequency modulation. If the DAC is less
than perfect it will toss in it's own "helpful stuff" as well.

It's not quite that simple of course. You have a dac width, a sine lookup
table size / resolution and a phase accumulator width. You can also dither
things. The stuff above will at least get you pointed in the right
direction. 

Bob 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Hal Murray
Sent: Thursday, October 25, 2012 12:45 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Adjusting HP 5065A frequency


lists at rtty.us said:
> The gotcha with the DDS is phase truncation. That pretty much trashes the
> ADEV. 

Thanks.

How should I think about the output of a DDS?

Lets assume I'm interested in the frequency domain where the "error" is 
measured in phase noise.  For a DDS, I think they are spurs.

Suppose I have a clock running at 101 MHz and I want 10 MHz.  Is the output 
10 MHz with some spurs, or 10.1 MHz with some spurs?

Are there rules of thumb for the size and location of the spurs?  (given the

input freq and output freq)


-- 
These are my opinions.  I hate spam.




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