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

[Bruce Griffiths]

John Ackermann N8UR wrote:
> 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?
>
>   
John

When measuring the phase noise of amplifiers and other devices with
relatively low phase shifts at 10MHz (or 5MHz) one can start with a
quadrature hybrid to produce test and reference signals in approximate
quadrature. One then only has to compensate for the UUT delay using an
splitter an, attenuator and another quadrature hybrid to produce the
small phase shift required.
One can even use a mixer as a dc controlled attenuator for the fine
phase adjustment to interpolate between attenuator steps.

Bruce