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.griffi...@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.griffi...@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.griffi...@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 >>>>>> >>>>>> ewkeh...@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.griffi...@xtra.co.nz writes: >>>>>>> >>>>>>> ewkeh...@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 >>>>>>> >>>>>>> >>>>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- time-nuts@febo.com >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>> and follow the instructions there. >>>>> >>>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>>> >>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > <DualCEBuffer3.gif>_______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.