DMTD board

[5065AGuru]

From the data sheet:

"The MC1650 and the MC1651 are very high speed comparators utilizing differential amplifier inputs to sense analog signals above or below a reference level. An output latch provides a unique sample-hold feature. The MC1650 provides high impedance Darlington inputs, while the MC1651 is a lower impedance option, with higher input slew rate and higher speed capability."

The nice thing about using them as an input stage is the wide input range you get. 100mv to over 6v.
The other dual mixers I have must be carefully fed a specific level for best performance and to prevent damage to the mixers.
Also they have balanced outputs so you can drive the mixers that way.
Not sure what that does for performance???

So far testing is looking good with a couple minor changes made to the circuit.
I'd say another week of testing and  I'll be happy with it.

Cheers,

Corby

[notfaded1]

OK, Here is a plot of the noise floor of the simple dual mixer.
This is good enough for pretty much any TimeNut!
Bill of materials will follow, Then the schematic, and then a corrected express PCB file.
(I need to enlarge a couple holes.)
The prototype is spoken for but the other two bare boards including some of the harder to find parts included will be offered for sale. (Pretty much at cost!)
This will be after I have a chance to do some more testing to make sure I'm happy with the design.

Cheers,

Corby

The noise floor figures look totally legit!  It's hard to argue with that. 

[notfaded1]

Hello,

I don't have found many clear info about this with a Google search, so I ask you :
Does somebody can explain what is the purpose and applications of this DTMT board ?
How it work ?
Regards.

Frex

Close Frex but search for DMTD instead... easy to mix these letters up... I've done it myself before that's how I know.  I think maybe it's old DTMF push button phone tones ringing in the back of head after all these years.  Brings back memories... we used take the old hand held DTMF phone dialers from Radio Shack and replace the timing crystal in the back.  This made one * star a nickel, 2 * stars a dime, and 5 * stars a quarter sound out of the speaker on the back.  Perfect portable Red box for pay phones... back when we had pay phones!

Bill

[tkamiya]

I still can't remember that 4 letter combination!  I have to look it up every time.  I'd say there are too many acronyms in this world.

[rubidium]

Close Frex but search for DMTD instead... easy to mix these letters up... I've done it myself before that's how I know.  I think maybe it's old DTMF push button phone tones ringing in the back of head after all these years.  Brings back memories... we used take the old hand held DTMF phone dialers from Radio Shack and replace the timing crystal in the back.  This made one * star a nickel, 2 * stars a dime, and 5 * stars a quarter sound out of the speaker on the back.  Perfect portable Red box for pay phones... back when we had pay phones!

Bill

Ha! You're dating yourself, buddy! Back in the day, we used those recordable Hallmark greeting cards when they first came out.   

[awallin]

The noise floor figures look totally legit!  It's hard to argue with that. 

almost too good to be true!?
Riley reports ca 5e-13 @ 1s http://www.stable32.com/A%20Small%20DMTD%20System.pdf
3120A/TimePod or the newer 53100A is around  3...4e-14 @ 1s http://www.miles.io/PhaseStation_53100A_user_manual.pdf
Ettus SDR around 7e-14 @1s  https://arxiv.org/abs/1605.03505

[KE5FX]

In principle, if the front-end noise is low enough (and white enough), it's possible to see useful results all the way down at this level.  Just a matter of setting the appropriate measurement bandwidth... presumably 0.5 Hz or so for your current setup, right, Corby?

Taking full advantage of a floor that low can be tricky, as even your cables will conspire against you.  At 3E-15 @ t=1s, you probably need 140+ dB of port isolation to avoid beatnotes between closely-spaced 10 MHz sources.  Definitely achievable, but it usually doesn't happen by accident!

[thinkfat]

The real-world sanity check would be the "RG58 hot vs. cold". Not sure about the effect, but I guess the cable simply got longer due to thermal expansion? If the noise floor is off by a magnitude, this should reveal it. The cable changed length corresponding to a 40ps phase shift.

PS: looks like phase shift is not linear with temperature ("Teflon Knee")

[awallin]

The real-world sanity check would be the "RG58 hot vs. cold". Not sure about the effect, but I guess the cable simply got longer due to thermal expansion? If the noise floor is off by a magnitude, this should reveal it. The cable changed length corresponding to a 40ps phase shift.

in the coffee-cup post "noise level is in the 20 to 50 FemtoSecond range." - but I don't understand how this goes together with the ADEV-floor which seems to be plotted at ca 3e-15 @ 1s (if I read the figure correctly...).
EDIT: the post on page 1 has now been edited to show a noise-floor of ca 2e-13 @ 1s, a mere 100-fold de-rating from the initial figure...

For white-noise 20 fs amplitude (or peak-to-peak?) @ 1s I would assume there's a sqrt(3) factor to give an ADEV-floor around 3.5e-14 @ 1s, which is very much in line with the references posted above, but 10-fold higher than the ADEV-floor figure from the post above.

[thinkfat]

I'd still take it. I doubt I could create an environment silent enough to realize a 3e-15 noise floor.

[FriedLogic]

in the coffee-cup post "noise level is in the 20 to 50 FemtoSecond range." - but I don't understand how this goes together with the ADEV-floor which seems to be plotted at ca 3e-15 @ 1s (if I read the figure correctly...).

Just a guess: one is a basic test through what does not look like super high quality cable and connectors, and the other likely done with very much more suitable cabling. I'm sure we'll hear anyway.

[notfaded1]

There are some cables that don't exhibit the same issues PTFE dielectric has.  See attached used in radar and other applications where phase is of extreme importance.

Bill

[5065AGuru]

OK, My bad somewhere!

You are correct. The Noise floor plot is too good!

2.67X10-15th at 1 Sec is not realistic.

I'm not sure if I messed up the scaling or what.

I don't have the file with me but I'll check tomorrow and see what happened.

The SMDfirstrun AD plot however has correct scaling.

Cheers,

Corby

[Mrt12]

Hi Corby,
so do you really drive the mixers with square waves from those ECL drivers?
I knew that it is possible to use a square wave for the LO input, but does it work equally well if both the RF and the LO are square waves? is the performance comparable or even better than if sine waves were used? and: how does the signal at the IF port look like? I am really curious for the schematics.

[5065AGuru]

MRT12,

Yes the mixers are driven by square waves.
This was how it was done in the EFRATOM TS105A, so I know it works.
Not sure how it would compare to sine inputs but this whole exercise was to make a low parts count unit that had a wide input amplitude range for an entry level Dual Mixer unit.
Still testing and hope to have some good data by the first of next week.
Schematics and Express PCB file will follow.
Next post I hope to have a composite plot that compares my 3 current Dual mixer units, one I got rid of, another complex unit, and the simple dual mixer.
That will let us see how it stacks up.

Cheers,

Corby

[thinkfat]

For the mixers its all the same I guess. They will just see a LO and RF that are rich in tones and happily multiply them all. As long as the high-order products are far enough away from the fundamental, the low-pass after the mixer will get rid of them.

[ch_scr]

I do not know the schematics but if only a "fast" comperator with differential out is needed maybe the LM360 could be used?

[thinkfat]

AD8612 would be suitable, too, I guess. But I'm more concerned about the mixers. The MiniCircuits stuff is really nice, but I need to find a distributor that stocks them. Digikey doesn't have them at all and Mouser refuses to sell them in Germany 

[notfaded1]

Now I had to look it up... the front panel display is so frickin' cool!  Dang!  How can you not love a classic display technology like that on a DMTD!  I have a collection of Nixie tube frequency counters including a Dekatron one.  I'll post some pics later.  Really neat devices!    I love that classic neon glow.

Bill

[tkamiya]

Corby,

Since you said "hard to get parts" are involved, I would like to see just a partial parts list (less jellybean parts) to get head start on sourcing them.  Would you mind doing that?

[FriedLogic]

Mini-Circuits appear to distribute from the UK now too, so that should be easier for those in the EU - for a couple of months anyway....

[thinkfat]

We may have to organize a group buy. Some parts have MOQ in the twenties.

[Mrt12]

But I am still wondering whether it is really a smart idea to drive the mixers with square waves. Assume you drive a mixer with sine waves, 10MHz and 10MHz+1Hz for the LO and RF.
The mixing products will be: 1Hz and 20MHz+1Hz.

Now assume that the mixer is driven with the same frequencies as above, but with square waves. The square waves each have the following spectral components:
10MHz, 30MHz, 50MHz for one signal, 10MHz+1Hz, 30MHz+3Hz and 50MHz+5Hz for the other signal.
When these two signals are mixed, the result at the IF output will contain the following frequencies (I list the difference frequencies only, as the sum frequencies are all well above 10MHz and can be easily filtered out):

1Hz (=10MHz+1Hz - 10MHz)
3Hz (=30MHz+3Hz - 30MHz)
5Hz (=50MHz+5Hz - 50MHz)

I don't think the IF output will be a square wave, but it will definitely contain a set of harmonics, so I wonder how this will work - because in this very case, we are actually only interested in the 1Hz frequency.

[tkamiya]

You are right about heterodyning square waves.  All of the harmonics will be mixed together and create whole bunch of spectrum impurities.  But levels are much lower.  I read somewhere DBMs work much more efficiently with square wave than sine wave due to switching action of the diode ring. 

Maybe someone can simulate it or run it through in lab.... 

Here's some reference:
https://www.microwaves101.com/encyclopedias/double-balanced-mixers

[notfaded1]

If it worked well for Efratom I'm not sure why it wouldn't work here?    Can't wait to see how it stacks up to other DMTD's.

I know how long it takes to run some of these tests.  I pretty much have at least one frequency experiment running at all times in my lab.  Lately I've been comparing the 5065 against 5061B, 5071A, and various Rb's I have.  I really like the old classic Efratom Rb's.  They really knew how to build a device in those days with nice large rubidium lamps in them.  I have an FRK-L and two M-100's.  Easy access to the Rb lamp too!  It's just a big machined screw on the back of the unit which, believe it or not, I believe was made so the lamp could be replaced while it's running although I've never tried this.

Bill