Hi Ok, RPD-1 #1 puts out 9.97 volts into a 500 ohm resistor to ground termination (no blocking capacitor). That's still well above the catalog spec. I'm running 25% more voltage than their 7 dbm. That still does not fully explain what I'm seeing.
The scope does indeed indicate 15 volts when I hook it to a 15 volt supply. Given the number of broken pieces of test gear I seem to own that was worth checking. ... Bob On Feb 28, 2010, at 8:54 PM, Bob Camp wrote: > Hi > > The Minicircuits guys claim 800 to 1000 mv / radian. In my units that would > be 5 to 6.2 volts per cycle. I believe I'm getting ~ 3 X that mostly from the > open circuit termination at audio. It's certainly something I could head back > downstairs and check. > > The < 10% increase in slope between resistive and capacitive termination has > never really been enough with the RPD-1 to make it seem to be worth it. It's > certainly worth it with a ZAD-3. > > Bob > > > On Feb 28, 2010, at g8:39 PM, Bruce Griffiths wrote: > >> The results for the RPD-1's are about what I expected: there's little >> difference in slope between either a 50 ohm +47nF termination or a 47nF >> termination. >> The slopes are about 6.5x greater than the values given by Minicircuits. >> (8mv/degree = 2.88V/cycle). I assume that they use 500 ohms connected >> directly to ground not via a capacitor. >> So there's something in NISTs claims of improved slope at least for the >> RPD-1. >> I suspect that NISTs original 50 ohm terminations were actually 50 ohms >> direct to ground not via a capacitor. >> Using a series capacitor increases the termination impedance at the beat >> frequency substantially over that when the resistor is connected directly to >> ground. >> >> Since its is also claimed by NIST and others that reactive termination >> reduces the noise, one also needs to measure the output noise spectral >> density for the various IF port terminations. >> >> Bruce >> >> Bob Camp wrote: >>> Hi >>> >>> Here's some data: >>> >>> The setup is very simple: >>> >>> Two oscillators at 10 MHz driving common base / 50 ohm output buffers. The >>> buffers ensure that the source impedance is really 50 ohms. One puts out >>> 9.3 dbm the other 9.5 dbm. They can be tuned for a beat note in the 0 to >>> 100 Hz range. >>> >>> The basic mixer termination filter is a pair cascaded / identical L >>> networks. Both have 10 uh in the series leg and 0.047 uf to ground in the >>> shunt leg. The "audio end" of the filter hooks straight into a digitizing >>> scope. >>> >>> The termination options for the mixer are: >>> >>> 1) inductive - just running into the 10 uh of the first L network. >>> 2) 50 ohms - drop a 57 ohm in series with 0.047 from the mixer output to >>> ground >>> 3) Capacitive - 0.047 uf to ground at the mixer output. >>> >>> The data is computed from the time to cross the center 50% of the output >>> waveform. If the output is 1V p-p then the data would cover the range -.25 >>> to +.25 volts. I've normalized it to "volts / cycle". Divide by 2* pi if >>> you want to get volts / radian. >>> >>> >>> mixer 50 ohms inductive >>> capacitive >>> >>> ZAD-3 3.51 2.96 9.98 >>> RPD-1 #1 17.77 10.50 18.85 >>> RPD-1 #2 17.40 10.058 18.53 >>> 10514A #1 5.796 4.396 10.31 >>> 10514A #2 5.826 4.406 10.33 >>> 10534A 5.402 4.078 10.88 >>> ZP3-MH 8.06 5.81 11.28 >>> ZAD-1H 7.73 5.93 9.38 >>> >>> Since not everybody has memorized mixer catalogs: >>> >>> ZAD-3 typical minicircuits 7 to 10 dbm mixer >>> RPD-1 500 ohm output phase detector (50 ohms is the "wrong" >>> termination for it) >>> 10514, 10534 HP products from a ways back >>> ZP3-MH a 13 dbm class mixer, 9 dbm should be under driving it >>> ZAD-1H a 17 dbm class mixer, should be 8 db under driven. >>> >>> Bottom line - Capacitive termination helps some parts more than others. The >>> RPD-1 does not get a real big boost, but the ZAD-1 certainly does. There's >>> no real way to know what it's going to do without checking your mixer under >>> your conditions. >>> >>> A few other notes: >>> >>> 1) The measurement technique slightly under states the slope for the 50 ohm >>> case. Since the beat note is approximately a sine wave in all cases, the >>> true slope at zero is a bit higher than this technique indicates. >>> >>> 2) The Inductive termination gives the widest linear region. The output is >>> very nearly an ideal triangle wave. It would make the best "wide range" >>> phase detector. >>> >>> 3) The terminations are not precise, but they are identical in all cases. A >>> more purely inductive load could be constructed. The parts are just what I >>> had lying around. >>> >>> 4) No strange bumps or peaks were detected in the beat notes of any of the >>> mixers. Never seen one, regardless of what NIST says they have seen. >>> >>> 5) Eventually I'll go back and check the RPD's with 500 ohms. I stuck with >>> 50 simply to keep everything as "same same" as I could. >>> >>> 6) Sweeping the beat note from 100 Hz to 1 Hz showed no change in the >>> output amplitude. >>> >>> 7) Contrary to my previous post the peak-peak output voltages are within >>> 10% for all terminations. Slope and peak to peak are different things..... >>> >>> 8) All mixers are running into essentially an open circuit load at audio. >>> The scope input is> 1 M ohm and the capacitive reactances are>100 K ohms. >>> >>> 9) No attempt was made to set up directional couplers and figure out what >>> the "real" input to the mixers actually is. Ditto on playing with series >>> resistors to improve the match. >>> >>> So there it is. Anybody else got some data to compare to. >>> >>> Bob >>> >>> On Feb 28, 2010, at 3:53 PM, Bruce Griffiths wrote: >>> >>> >>>> My simulations indicate that terminating the Mixer IF port in an RF short >>>> (with both RF and LO ports saturated) increases the beat frequency zero >>>> crossing slope by more than a factor of 2 (exact value depends on mixer >>>> component characteristics) but doesnt significantly increase the beat >>>> frequency amplitude over that with a high value resistive termination. To >>>> achieve this the IF port termination impedance needs to be high at the >>>> beat frequency and its significant harmonics. The value above which the >>>> impedance is considered high depends on mixer details such as transformer >>>> turns ratio, RF source impedance, diode characteristics and RF input >>>> levels, etc. >>>> >>>> Bruce >>>> >>>> Bob Camp wrote: >>>> >>>>> Hi >>>>> >>>>> Putting The C on the feedback R in a positive gain setup is only going to >>>>> take the "roll off" gain down to 1. Doing the same with an inverting amp >>>>> or using a series R / cap to ground will drop the gain a lot more in the >>>>> roll off region. >>>>> >>>>> I would worry about any resistor that's marked as 10K and reads 20K. It's >>>>> likely noisy. >>>>> >>>>> A typical DBM has a loss of 5 to 7 db when not in compression. With a +7 >>>>> to +10 dbm drive that should give you an output of 0 to 2 dbm . The >>>>> mixer output should be in the .6 to .8 V p-p range into 50 ohms. You >>>>> should get about twice that on the beat note running into a load> 500 >>>>> ohms. A gain of 20 should be plenty. That would give you .6 x 2 x 20 = >>>>> 24 V p-p out of the amp. >>>>> >>>>> If you "rf short" the output of the mixer you may double the beat note >>>>> again (total of 4X the 50 ohm value). Net would be a 2.4 to 3.2 V p-p >>>>> beat note. Anything much over a gain of 10 would be a problem then. This >>>>> is one of the cases where 2 X 2 probably does not = 4, so measurements >>>>> are indeed in order. >>>>> >>>>> >>>>> Bob >>>>> >>>>> >>>>> >>>>> >>>>> On Feb 28, 2010, at 1:01 AM, Brian Kirby wrote: >>>>> >>>>> >>>>> >>>>>> The values in the schematics are wrong for the op amp gain. The drawing >>>>>> was from an earlier drawing where I made a preamp to start checks on the >>>>>> mixers, and I sent it to you (Bruce G). Thats when you determined I did >>>>>> not have enough gain to get near the noise floor. The THAT1512/1646 ICs >>>>>> were ordered to make a new preamp for the future measurements on the >>>>>> mixers. >>>>>> >>>>>> When I use the scope and check the outputs of the IC, I have 20 volts >>>>>> peak to peak, sine-wave. I know from previous readings I see about 500 >>>>>> mv p-p out of the mixer. >>>>>> >>>>>> I went down to the bench and the resistors I used were still there (I >>>>>> bought several taped reels of Dale RN55D resistors when a local business >>>>>> went out). I used 294 ohms and 14.9 kilo-ohms, for a gain of 50 (the >>>>>> power rails are +/- 15 volts). Also not shown on the schematic is a >>>>>> 0.47 uF cap around the 14.9 kilo-ohm resistor. I think I was trying to >>>>>> limit the bandwidth to around 15 hertz. >>>>>> >>>>>> Also the resistor going between the op amp and the limiting diodes was >>>>>> marked 10K, its 20K. The diodes are 1N4148. Corrected drawing attached. >>>>>> >>>>>> This is what happens to time nuts who can only play on the weekend and >>>>>> stay up all night....and my employer just thinks I party too >>>>>> hard.....for Monday mornings. >>>>>> >>>>>> >>>>>> >>>>>> Brian KD4FM >>>>>> >>>>>> >>>>>> >>>>>> Bruce Griffiths wrote: >>>>>> >>>>>> >>>>>>> The LT1037 is shown with a gain of ~1690x, if this amplifier is used to >>>>>>> amplify the beat frequency signal, it will saturate. >>>>>>> Opamp recovery from saturation is poorly documented and may be very >>>>>>> slow. >>>>>>> It would be better to use some diodes in the amplifier feedback network >>>>>>> to limit the large signal gain to 5x (so that the LT1037 remains stable >>>>>>> as it isn't unity gain stable). >>>>>>> This will ensure a somewhat faster recovery from overload as the LT1037 >>>>>>> then avoids saturation and the opamp input stage remains in the linear >>>>>>> region. >>>>>>> >>>>>>> Bruce >>>>>>> >>>>>>> Bob Camp wrote: >>>>>>> >>>>>>> >>>>>>>> Hi >>>>>>>> >>>>>>>> Assuming that the junction of the back to back diodes goes trough a >>>>>>>> chunk of coax to get to the counter: >>>>>>>> >>>>>>>> You are forming a low pass filter with the 10K resistor and the coax >>>>>>>> capacitance. The LT1037 is quite happy driving a 600 ohm load. You >>>>>>>> could easily drop the impedance at that point below 300 ohms. That >>>>>>>> should give you a faster edge into the counter. >>>>>>>> >>>>>>>> You also should check the slew rate performance of the 1037. You don't >>>>>>>> want the op amp to be slew rate limited. >>>>>>>> >>>>>>>> Bob >>>>>>>> >>>>>>>> >>>>>>>> On Feb 27, 2010, at 12:41 PM, Brian Kirby wrote: >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>>> I am in the process of designing a DMTD system. As an experiment to >>>>>>>>> do basic measurements on the chosen mixer, I used a capacitor (0.01 >>>>>>>>> uF) in series to ground with a 47 ohm metal film resistor. Where the >>>>>>>>> capacitor and resistor meets, another resistor is attached (390 ohms) >>>>>>>>> that goes to ground. The idea is to provide a 50 ohm termination at >>>>>>>>> 20 Mhz and a lighter termination at audio frequencies. I seen this >>>>>>>>> is a NBS note and I can say, its a starting point for my experiments. >>>>>>>>> >>>>>>>>> This (my) system is designed for 10 Mhz, using a 10 hertz beat. A >>>>>>>>> schematic is attached of what I am experimenting with at the moment. >>>>>>>>> A HP5370B is the recording instrument. The noise floor from 1 days >>>>>>>>> observations show 2x10-11 at 0.1 seconds, 2x10-12 at 1 sec, 5x10-13 >>>>>>>>> at 10 sec, 6x10-14 at 100 sec, 7x10-15 at 1000 sec, and 7x10-16 at >>>>>>>>> 10,000 secs. It will be interesting when the project is completed >>>>>>>>> to see how much improvement there will be. >>>>>>>>> >>>>>>>>> As I understand (or learning..) mixer performance is the key to the >>>>>>>>> DMTD system. It occurs to me that maybe a capacitor designed for 50 >>>>>>>>> ohms at 20 mhz may be a better termination (for the IF port) for this >>>>>>>>> mixer. A 16 pF capacitor is 50 ohms at 20 mhz, and for comparison at >>>>>>>>> 10 hertz, it would be 100 meg-ohms, which would give maximum >>>>>>>>> amplitude at 10 hertz. As I understand, a capacitor terminated >>>>>>>>> mixer will give a triangle wave output, which is very beneficial to >>>>>>>>> the design - as the end result is to get maximum slope out of the >>>>>>>>> mixer. I would say, unqualified as I am, the capacitor termination >>>>>>>>> matches the 20 mhz signal, and helps attenuates the harmonics of the >>>>>>>>> mixer, and has no , or very little effect on the audio frequencies >>>>>>>>> that we are interested in. >>>>>>>>> >>>>>>>>> And saying/rambling on... that if maximum slope is needed, its needed >>>>>>>>> on the 10 hertz beat signal - so maybe a capacitive termination on >>>>>>>>> the 10 hertz signal only and something resistive on the 20 mhz >>>>>>>>> signal........another idea use the 16 pF direct off the mixer, then a >>>>>>>>> series resistor for isolation and then a large capacitor on the 10 >>>>>>>>> hertz beat for maximum slope. >>>>>>>>> >>>>>>>>> At the present, I am awaiting parts to build a low noise preamp base >>>>>>>>> on the THAT1512 so I can make better measurements on the mixer. >>>>>>>>> Bruce has provided a lot of good suggestions and helpful comments on >>>>>>>>> my project and Ulrich has provided me quite a bit of user support on >>>>>>>>> his program, Plotter. Thanks to all. >>>>>>>>> >>>>>>>>> Comments ? Brian KD4FM >>>>>>>>> <DMTD_Plans.pdf>_______________________________________________ >>>>>>>>> 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. >>>>>>> >>>>>>> >>>>>>> >>>>>> <DMTD_C_Plans.pdf>_______________________________________________ >>>>>> 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.
