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

[Bruce Griffiths]

Magnus Danielson wrote:
> Bruce Griffiths skrev:
>   
>> 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.
>>     
>
> Using two mixers programmed by two individual DC signals the quadrature 
> signal can be setup to arbitrary phase shift. It is trivial to combine 
> programmed damping and phase-shift in this fashion.
>
> Cheers,
> Magnus
>
>   
Hej Magnus


See patent US3803499 for one implementation of this scheme.**

**However, where possible, a lower noise more stable system usually
results when the phase shift provided by such a system is relatively
small.**

**Bruce