Hi Left out:
All the data was taken with a beat note of roughly 10.2 Hz Bob On Feb 28, 2010, at 8:11 PM, 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.
