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.
