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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 24 02:34:42 UTC 2008


Hej Magnus

Magnus Danielson wrote:
> Hej Bruce,
>
>   
>> Hej Magnus
>>
>> Thats true, but I had the more general case in mind wherein which one
>> adds coarse fixed delay increments as required and merely uses the
>> variable gain mixer to make a fine adjustment to the phase.
>>     
>
> How do you intend that to work? Slightly introduce the signal with a 
> different but nearby phase?
>
>   
Simple, use a splitter (0 degree, 90 degree, 180 degree as appropriate)
to separate the signal into 2 parts one for the LO, one for the DUT.
Add some fixed delay to the LO branch then use a 90 degree splitter, 
attenuate the 90 degree  output  and add it (a hybrid combiner/splitter)
to the  0 degree output, thus phase shifting the  final output by a
small adjustable amount.
>> No real need for sine and cosine weighting for small phase adjustments
>> as the effect on the amplitude will be small and phase noise measurement
>> systems are usually relatively insensitive to AM.
>>     
>
> Certainly, but various delay-adjustments will provide different output 
> levels, which can be handled in a sub-sequent scaling or by weighing the 
> signal of different levels.
>   
Probably a simple calibration will suffice when using a saturated mixer
used as a phase detector.
> To achieve an arbitrary (0-360 degree) phase-shift with such a system 
> may be a viable question. Running a set of cables and a programable 
> multiplexer of some sort would be possible.
>
> Well, that was not what was asked for originally, and also not apparent 
> from your original comment. Surely you can achieve better performance 
> than this quad-phase circuit provides, but since it was not described 
> what type of circuit you intended it never became clear what you meant.
>
> The original question infact was for a system where you do not use fixed 
> delays such as cables.
>   
I reinterpreted it to mean that some fixed delays would be OK as long as
they don't have to be accurate to within better than a few nanosec.
In most cases ( eg when measuring isolation amplifier phase noise at
10MHz ) such lumped delays probably wont be necessary as the amplifier
delay will be relatively small.
> Cheers,
> Magnus
>
>   
Bruce



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