Hi The reverse isolation issue is indeed one of the weaknesses of this setup. For testing OCXO’s isolation is not a big deal. A normal OCOX has very good output buffering to give it the stability you are after. If you are running (maybe) a VCO with no buffering, that assumption falls apart. The VCO will / can injection lock through the mixer. In that case you *do* need an amp to provide enough isolation to prevent the injection lock.
Bob > On Mar 25, 2016, at 12:27 AM, Bruce Griffiths <[email protected]> > wrote: > > http://www.ko4bb.com/getsimple/index.php?id=low-noise-high-reverse-isolation-low-distortion-rf-amplifier > Bruce > > > > On Friday, 25 March 2016 4:57 PM, Bruce Griffiths > <[email protected]> wrote: > > > If 40-50dB reverse isolation is sufficient one can easily build suitable low > gain (<10dB) amps with a single RF transistor (plus output transformer > together with a low frequency transistor plus LED for bias stabilisation). > Retrofitting a similar biasing scheme to the RF amps in some early HP PN > measurement gear apparently does wonders for their PN at low offsets. > One could even use a square wave drive from the output of a 74UHS125 or > similar CMOS buffer to drive the phase detector input. There is a NIST paper > that indicates a square wave LO drive for some mixers improves the > performance somewhat. > > If reverse isolation isnt an issue a pushpull transformer feedback Norton amp > works well. > > I just bought the HELA10's on evaluation PCBs complete with brass metalwork.. > > Bruce > > > > On Friday, 25 March 2016 4:02 PM, Bob Camp <[email protected]> wrote: > > > Hi > > If you think the HELA10 is fun at 10 MHz, try it at 1 MHz :) > > The RPD-1 is a 1 MHz to 100 MHz part. That pretty well covers *most* of the > low > phase noise OCXO’s that people find running around in their junk boxes. To be > “general purpose”, an amp would need to cover the same range. With two OCXO’s > and two mixers, you would need 4 amps if they are after the splitters. By the > time you > get even the HELA10’s on heatsinks and boards you probably are around $40 an > amplifier. Finding a part that is “as good as” the HELA10 is at 100 MHz, but > at 1 MHz, > is not very easy …. > > ===== > > Sort of on a bit different part of the same topic: > > There is nothing magic about the RPD-1 other than it is easy to dead bug and > attach leaded > parts to. If one is doing a pc board, the SYPD-1 is the same thing in a > cheaper > surface mount package. The $5.70 you save will pay for a few square inches of > pc board. > > Bob > > >> On Mar 24, 2016, at 9:31 PM, Bruce Griffiths <[email protected]> >> wrote: >> >> Actually if you split the signal and then amplify each output independently >> then the PN performance of the RF amps is not too critical in that cross >> correlation averages the amplifier PN down as well as that of the >> mixers.I've done this with the Timepod using quite noisy amps as nothing >> else was immediately to hand.It just takes a little longer but works very >> well. I measured the output PN noise of an LTC6957 evaluation board this way >> using a couple of minicircuits HELA10s which are fairly noisy at 10MHz. >> If you don't need a PN floor below -180dBc/Hz then there are simple >> inexpensive one transistor (plus another for biasing) circuits that will >> achieve a few dB of gain with a PN noise floor well below -170dBc/Hz.The >> only real limitation is due to the presence of anti correlated thermal noise >> at the splitter outputs. >> >> Bruce >> >> >> On Friday, 25 March 2016 2:06 PM, Bob Camp <[email protected]> wrote: >> >> >> Hi >> >> That’s another good point about the need to work out a target device. Both >> of the possible target devices I mentioned have enough channels to do at >> least a >> dual channel measurement. That would add another mixer and a pair of power >> splitters along with another amp chain. >> >> The other part of that news is the RF drive power required goes up. You can >> do a pretty good job >> of saturating an RPD-1 with +7 dbm. Most (but not all) OCXO’s and other >> gizmos will >> provide that without any amplifiers involved. Adding a 3 db splitter gets >> you into the 10 dbm >> range. That is getting fairly close to the limit for a lot of devices. >> >> You can add an amp. The ones that work without impacting the phase noise of >> a high quality >> OCXO cost as much as the audio cards or USB devices. Cost wise, I’d keep >> that sort >> of thing off the main board. >> >> So what is the second channel worth? >> >> The basic single channel design will get you into the -173 to -176 dbc / Hz >> range on a fairly high >> power pair of OCXO’s. The cross correlation “stuff” will get you past that >> point. Is that worth taking >> the BOM (without board and power supply) up to $80 or so? Consider that with >> the board and >> power supply, it likely is over $100. >> >> Would I do it as an accessory to a Janus or QA401? Maybe. You would need to >> pick one or >> the other. In the case of the Janus, there are more software issues and some >> noise floor testing. >> The QA401 is mighty expensive. The original idea was to use the sound card >> you already have …. >> >> Bob >> >> >>> On Mar 24, 2016, at 5:30 PM, Bruce Griffiths <[email protected]> >>> wrote: >>> >>> If the software implements acquisition of cross power spectra >>> Then one could implement a near state of the art cross correlation PN test >>> set >>> based on this. >>> With a suitable preamp the sound card could also be used for power supply >>> and >>> reference noise measurement. >>> >>> Bruce >>> >>> On Thursday, March 24, 2016 04:54:47 PM Bob Camp wrote: >>>> Hi >>>> >>>> The board is pretty non-critical. It’s 90% audio. The biggest hassle is a >>>> power supply. You would *like* a fairly high voltage, at least if you are >>>> driving a spectrum analyzer. That may not be quite the case with a sound >>>> card. It depends a *lot* which one you are running. Something like a QA401: >>>> >>>> https://www.quantasylum.com/content/Products/QA401.aspx >>>> >>>> Would make a good target device. It’s based on the AKM 5397 So might some >>>> Janus boards. They are based on the earlier(?) AKM 5394. The QA401 has the >>>> advantage of a nice box and full USB isolation (ground loops are a pain).. >>>> It also has drivers and all the OS hooks. The Janus is a bit more “DIY” >>>> with no drivers or interface (let alone isolation). The Janus is < 1/4 the >>>> price. >>>> >>>> The high voltage (+/- 18V linear regulated) supply approach makes a lot of >>>> sense with the QA401. It probably does not make as much sense with the >>>> Janus. Switching regulators of any sort are something I would strongly >>>> recommend against in a system like this that is trying to measure noise >>>> floor at audio …. >>>> >>>> The schematic changes a bit depending on what the target is. I can draw it >>>> up if there is a consensus on the target. One example: If the “sound card” >>>> is DC coupled, you can use it to indicate (and check) quadrature. If it’s >>>> an AC device, you need some sort of isolated output for another indicator. >>>> >>>> Bob >>>> >>>>> On Mar 24, 2016, at 1:31 PM, John Ackermann N8UR <[email protected]> wrote: >>>>> >>>>> I'd be willing to assist with board layout if someone wanted to make this >>>>> into a real project (e.g., fully developed schematic). TAPR might be >>>>> talked into supplying at least bare boards; we'd have to get a sense of >>>>> demand before committing to a full kit or assembled unit. >>>>> >>>>> John >>>>> ---- >>>>> >>>>> On 3/24/2016 9:04 AM, jimlux wrote: >>>>>> More like $40 in parts, without a board, etc. >>>>>> The RPD-1 is $20.70 >>>>>> LT1678/LT1679 is a nice low noise opamp that does rail to rail and is >>>>>> about $5 >>>>>> etc >>>>>> >>>>>> On 3/24/16 4:42 AM, Bob Camp wrote: >>>>>>> Hi >>>>>>> >>>>>>> Pretty simple: >>>>>>> >>>>>>> Double balanced mixer, RPD-1 is one option, there are others. >>>>>>> >>>>>>> Fairly simple L/C lowpass between the mixer and an op-amp. >>>>>>> >>>>>>> 20 db positive (non-inverting) op-amp amplifier string after the mixer >>>>>>> >>>>>>> Output of the string goes to the sound card. Use a good (dual / quad) >>>>>>> audio op amp >>>>>>> >>>>>>> Quadrature amp picks off the output of the first op amp stage, switch >>>>>>> and resistors to set gain, pot to set op point. >>>>>>> >>>>>>> ==== >>>>>>> >>>>>>> So what you have is an old style quadrature phase noise amp and “PLL”. >>>>>>> More or less a very junior version >>>>>>> of the 3048 test box. Like any setup of this sort, you check two >>>>>>> similar oscillators. They run in quadrature and >>>>>>> you do a few “measure this with switch in position A” sort of things >>>>>>> to set things up each time. >>>>>>> >>>>>>> Nothing exotic. >>>>>>> >>>>>>> Bob >>>>>>> >>>>>>>> Any documentation on this $40 phase noise test set? >>>>>>>> >>>>>>>> Rick N6RK >>>>>> >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- [email protected] >>>>>> To unsubscribe, go to >>>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>>>> and follow the instructions there. >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to >>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the >>>>> instructions there. >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the >>>> instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
