[time-nuts] New topics (was Re: He is a Time-Nut Troublemaker....)

John Ackermann N8UR jra at febo.com
Tue Dec 23 20:28:47 UTC 2008


Hal Murray said the following on 12/23/2008 01:58 PM:
>> 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)

If doing phase noise or short term stability measurements, wouldn't the
noise of the DDS impact the results?



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