[time-nuts] Nifty "MINI TIC" for DMTD work detail Info please read

[Bob Camp]

Hi

Given that common practice is to mis-match the IF port on the mixers, it's probably not realistic to depend on exact match for isolation. Simple / cheap common base buffers likely are a better approach. Lots of isolation and not much flicker noise. 

Bob

On Nov 20, 2012, at 9:01 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> The details about matching (if any) used in the Czech DMTD would be informative.
> 
> To avoid degrading the performance of the DMTD system below that imposed by the mixers any isolation amps used will need a flicker phase noise floor below that of the mixers.
> Even an opamp based isolation amplifier can be at least 10dB quieter (for offsets of 10Hz and below) than a typical minicircuits RF amp.
> This is still about 10dB or so worse than a good mixer.
> A well designed low gain isolation amp built with discrete transistors can have significantly lower additive phase noise than an opamp.
> 
> To reduce the DMTD system noise one can either:
> 
> 1) Carefully match all ports using series resistors, pads etc as necessary to achieve the required isolation together with a high output low flicker phase noise amplifier to drive the splitter
> 
> 2) Use isolation amplifiers with very low flicker phase noise.
> 
> Some isolation between the 2 RF inputs of a DMTD is usually necessary to avoid injection locking of the 2 sources being compared.
> 
> 
> Bruce
> 
> Bob Camp wrote:
>> Hi
>> 
>> Those isolation numbers are *highly* dependent on very good matching at all ports. That's rarely the case unless you have a bunch of pads running around the system.
>> 
>> Bob
>> 
>> On Nov 20, 2012, at 5:49 PM, Bruce Griffiths<bruce.griffiths at xtra.co.nz>  wrote:
>> 
>>   
>>> Typical Minicircuits SMT RF amps have a phase noise at best 20dB worse (@10Hz offset) than the mixer/phase detector.
>>> Their reverse isolation is quite low (<<40dB)
>>> 
>>> The principle reason that the Czech DMTD has such low internal noise is due to the absence of any isolation amplifiers.
>>> They use the outputs of a 2 way splitter to drive the LO inputs of the mixers.
>>> 
>>> A output to output isolation of 40dB or more at 10MHz is possible with some minicicuits splitters (e.g. SYPS-2-1).
>>> The ZRPD1 has an RF1 - RF2 isolation of around 70dB at 10MHz.
>>> 
>>> With a channel to channel isolation of around 110dB for a 2x ZRPD1 + Splitter combination isolation amplifiers may not be necessary.
>>> 
>>> Bruce
>>> 
>>> Bruce Griffiths wrote:
>>>     
>>>> Since mixer noise is one of the limiting factors using a mixer with low flicker noise will help.
>>>> NIST found that a custom mixer using diode connected (collector base short) 2N222As had a significantly lower flicker phase noise than either the ZRPD1 or the 10534A.
>>>> They used off the shelf 1:5 impedance ratio transformers (probably from Minicircuits).
>>>> Another issue is the flicker phase noise of any isolation amplifiers used.
>>>> This is particularly critical if each mixer uses its own isolation amplifiers.
>>>> 
>>>> My current amplifier phase noise measurement setup (for measuring the additive PN of a pair of well matched amplifiers) has a self noise of around -170dBc/Hz @ 1Hz offset for a 10MHz input.
>>>> Ideally the additive phase noise of any isolation amplifiers should be well below that of the mixers.
>>>> 
>>>> Bruce
>>>> 
>>>> EWKehren at aol.com wrote:
>>>>       
>>>>> Yes Bruce I have the paper. I am not suggesting to copy it verbatim but if
>>>>> there is a way to reach reasonable priced 1 E-14 members of the list should
>>>>> pipe  in. I am willing to do an other board. the rest of the systems well
>>>>> on its way.  Einally after three years.
>>>>> Bert Kehren
>>>>> 
>>>>> 
>>>>> In a message dated 11/20/2012 3:28:57 P.M. Eastern Standard Time,
>>>>> bruce.griffiths at xtra.co.nz writes:
>>>>> 
>>>>> EWKehren at aol.com wrote:
>>>>>         
>>>>>> The D/M is being revisited  because  of the counter performance. 1 E-13 is
>>>>>> easily attainable  but the Czech IREE  published a paper and claim 2 E-15.
>>>>>> 
>>>>>>           
>>>>> Do you mean the paper ""optimization of dual-mixer time-difference
>>>>> multiplier" ?
>>>>> The ZCD developed in this is a bit of a kludge and is far  from optimum.
>>>>> Reverse engineering the circuit from the description given in  the paper
>>>>> isn't too difficult.
>>>>> They claim an instrument limited ADEV of  ~7E-15 @ 1s.
>>>>> Do you have a copy of this paper?
>>>>>         
>>>>>> Bert  Kehren   Miami
>>>>>>  _______________________________________________
>>>>>> 
>>>>>>           
>>>>> Bruce
>>>>> 
>>>>>         
>>> 
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>>   
> 
> 
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