[time-nuts] New topics (was Re: He is a Time-Nut Troublemaker....)
Lux, James P
james.p.lux at jpl.nasa.gov
Tue Dec 23 19:07:47 UTC 2008
Several DDS parts from Analog Devices (e.g. AD9854, which runs quite warm) are dual quadrature.. And have adjustable phase offsets as well.
I think the single DDS parts also have a programmable phase offset of 14-16 bits. You have to be careful with the configuration bits, so that writing the phase register doesn't zero the phase accumulator.
They're all available as eval boards, too.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Hal Murray
> Sent: Tuesday, December 23, 2008 10:59 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] New topics (was Re: He is a Time-Nut
> Troublemaker....)
>
>
> > 2. Several measurement techniques require a given phase
> relationship
> > (e.g., quadrature) between DUT and reference. For HF
> frequencies (ie,
> > 5 or 10 MHz) is there a *practical* phase shifter design covering
> > 180+ degrees that doesn't involve switching various lengths of coax
> > in and out of the line?
>
> PLL up by a factor of N, use that to drive a DDS, then
> filter. Maybe a pair of DDSes will get better tracking.
>
> For each possible phase offset, you need N slots in the
> table. (N/4 with more work)
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