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

[Magnus Danielson]

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