[time-nuts] Nifty "MINI TIC" for DMTD work detail Info please read
Bob Camp
lists at rtty.us
Wed Nov 21 06:53:56 UTC 2012
Hi
A pair of common base amps will get you to what ever your layout will permit. A single common base at 10 MHz should get you to at least 60 db with a little care. If you run a reasonable transistor you can run levels that will fry a 10 or a 13 dbm mixer. Again, all the discrete circuits work pretty well. It's the modular stuff (especially when driven hard) you have to watch out for.
Bob
On Nov 21, 2012, at 1:43 AM, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
>
> Reverse isolation at 10MHz is around 43dB.
> This can be improved significantly by using a Sziklai pair instead of a single transistor in each amplifier.
> However one could also do this in a CB amp.
>
> Since phase detectors require LO and RF input levels of around 10dBm either deign should suffice.
> NIST have shown that high level mixers appear to be somewhat noisier than either the ZRPD1 and 10534A.
> Whilst their custom mixer utilising diode connected 2N222A's has the lowest flicker noise the increased PCB board complexity may not be worthwhile for this application.
> Reducing the isolation amplifier noise contribution should be more effective than any other changes to the DMTD design.
>
> Bruce
>
> Bob Camp wrote:
>> 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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>>>>>>
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