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

Bob Camp lists at rtty.us
Wed Nov 21 05:10:37 UTC 2012


Hi

A few more parts and likely not quite as much isolation. None of that means it won't do a good job though. 

Bob

On Nov 20, 2012, at 11:20 PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:

> The attached circuit is somewhat more efficient and a little quieter.
> With a little elaboration lower distortion is possible.
> 
> Bruce
> 
> Bob Camp wrote:
>> 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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