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.
