DMTD board

[tkamiya]

I just ran numbers....  Would someone check if this is correct?

If input signal is 10MHz and it drifts 1Hz, that represents 1x10^-7 error.  Now, If this signal is down converted by hetrodyning to 1Hz, period is 1 second.  It would mean error of 1, but it also means 1 second error at 1Hz represents 1x10^-7 error for the original 10MHz.

That would mean 1 milli-second error at 1Hz (10^-3 ) represents 1x10^(-7-3) = 1x10^-10 at 10MHz
That would mean 1 micro-second error at 1Hz (10^-6) represents 1x10(-7-6) = 1x10^-13 at 10MHz
That would mean 1 nano-second error at 1Hz (10^-9) represents 1x10(-7-9) = 1x10^-16 at 10MHz

So, realistically, TICC counter only needs to resolve 100 nano-second to realize 1x10^-14 at 10MHz
(noise level of this DMTD circuit)  Common counter, HP53132 can resolve 500ps. 

Is this correct?

ps.
Corby,  you mentioned you have other DMTD.  What are they?

[ch_scr]

I started putting this circuit into Kicad (only schematic so far), and made the following selfish adjustments (because it fit's my part bin):
LM360 input comperators (comperator to SBL-1 circuit slightly modified), CA3000 as amplifier, fully differential IF filter right into the LM311 (made a LTSpice sim to make the filter act similar to the single ended one). Also added the series resistors on the output gates.
If someone would like to have a look (or use this as a starting point for there own shenanigans in Kicad) feel free.

[tkamiya]

Hi,

Assembled a second unit and the outputs were out of phase (for a common input).

The SBL-1 units on this one did not have the colored insulator to indicate polarity.

Since the board is laid out so that the SBL-1s are installed in opposite directions this matters,

Corby,

How did you test it to find out the polarity is reversed?  What are the symptoms?  I think signals are zero crossing and naturally out of phase.  I'm pretty confused as to what this means.  Thanks!

[5065AGuru]

Taka,

The unit functions a high resolution phase detector so if you feed two in phase RF signals in your outputs should also be in phase.
Of course as the DUT or REF drifts the RF signals will no longer be in phase but the outputs should follow.
Take one RF signal into a tee and feed both inputs from the tee, then on a scope both outputs should be high at the same time and transition low at the same time. With the inverted mixer one was high while the other low!

As far as resolution with an 8 digit counter, 5MHz inputs, and 1 1Hz offset the LSB = 2X10-15th

10Mhz and 1HZ gives and LSB of 1X10-15th

10.000001 00000000

The 1 is the 1HZ offset which is 1X10-7th the 8 digits after are the 8 digits of the counter with each digit one decade lower so -7 + -8 = -15 which is the LSB.

More on this when I start the tutorial post.

Cheers,

Corby

[5065AGuru]

Here is the stuffing diagram.

Blue caps are .1uf bypass caps
yellow caps are .01uf COG
red caps are .1uf COG or film (changed BOM)

[cncjerry]

Corby, Jerry here from time-nuts. 

Nice work, I haven't had a chance to read thru it all yet.  I just built Bill Riley's dual mixer setup using one of Bert's boards and it works great.  Wondering if there was a reason why you didn't use transformers on the input side?

As far as offset generators, I wanted to integrate a DDS into my DMTD system so I didn't have to screw around setting up and/or dedicating a more expensive generator just for testing.  So I bought and built one of the AD9910 DDS "kits" you can find on ebay with the external frequency generator input option.

I wanted to put 10Mhz directly into the AD9910 through a transformer but they way the implemented the chip in the kit software, you have to have a input frequency of 60Mhz or more so I am looking for a 10x digital multiplier to take my 10Mhz reference into 100Mhz.  Alternatively, I can change the software to enable the ref_clk multiplier and then the input frequency can by 3.2Mhz to 60Mhz but that looked like a ton of work.  I found that you can still inject 10Mhz into the board, but it uses the PLL in that mode and the frequency is a little off.  I've been using 10hz offset and instead of for instance, 9,999,990.000 000 the DDS output is measuring 9,999,990.002 53.  From what I understand the offset generator doesn't have to be that critical or phase locked to the reference but darn it, I wanted it to be!

if anyone is interested, the item number like the one I purchased is 64194186839.  DIY KIT for DDS AD9910 Arduino Shield RF Signal Generator.  Nice kit but a lot of smd soldering.  I used chip-quik low temp with a rework heat wand to flow the solder. Took a couple hours to build it even with my tremor.

I scanned the thread really quickly, but I didn't see a reference to Bill Riley's Dual Mixer but I'm sure I overlooked it.  I need another DMTD board so that I can run three-corner analysis.

Compared to my TICC alone and frequency counters including the FA2 and a couple other circuits I have for running stability tests, my DMTD enables me to collect tau's down to .01 or even lower with an offset of 100 and the limiting factor is the TICC.

Nice work,

Jerry

[5065AGuru]

Jerry,

I wanted to evaluate the TS105A circuitry mostly unmodified to see how it would do so did not try to add any bells and whistles!

I did not mention Riley's but probably should have as it has a good writeup.
Those DDS from eBay are nice but I'm pretty married to my 1Hz offset from an FTS 1200.
Does all I want and I don't choke on the big data files!

Cheers,

Corby

[cncjerry]

Corby,  I've heard of the FTS1200 but don't have one.  Can the EFC pull it 1hz (or more)?  I have a bunch of 10811s, you might remember you  sent me connectors, I think, and I've not been able to get the EFC to pull it that much.  I guess I could always do it the manual way and turn the screw... ha!

I wanted to be able to just push a button and do 1hz, 10hz or 100hz offsets.  I didn't think about it, but I wonder if using something that can hold like .5hz would be worth it as then you would get a really big multiplier.

I remember reading in Riley's paper, and then he sent me some emails, that the offset generator doesn't have to be all that accurate or phase locked to the reference.  Also, if you take two of your boards you can do three-hat (as you know) and factor out any of the three signals and that would take the offset out of the picture, I think. I only have tested my DMTD a little as after I built it the smoke up here drove me out of my office.

One parting comment, there was a mixer test done by I think it was NIST for NASA, or maybe the other way around, and a guy used the B-E junction of common transistors for the diode ring.  They then used 5:1 and inversely connected transformers and they claimed with tables and pretty graphs that the phase noise of their mixer whipped all the MCL versions.  I don't remember if the SBL-1 or TUF-3, etc were in that test, also don't know if it matters that much but since you did such a great job bringing the DMTD back to the masses here I thought I would mention it.

Lastly, since I wrote about that issue with the DDS, I found that they have used an external loop filter on the board.  So I'm going to do some reading to see if I can tighten up the PLL a little given I'll only be using the DDS around 10Mhz +/- 100hz.

Jerry

[thinkfat]

Having Gerber files would still be better. 3 boards done by Aisler will cost significantly less.

Here is what Express PCB sent to me. Hope it works for you!

The gerber files are formatted as RS-274-X files.  The drill file includes the hole size definitions.  The diameters listed refer to the finished hole sizes after plating, not the drill size.
Each file can be identify by it's extension:
    .TSK = top silkscreen layer
    .TSM = top solder mask layer
    .TOP = top copper layer
    .GTP = top paste layer
    .IPT = top inner copper layer
    .BOT = bottom copper layer
    .IPB = bottom inner copper layer
    .BSM= bottom solder mask layer
    .GBP = bottom paste layer 
    .DRI = drill file
    .OLN = board outline
    .CSV = pick and place

Took a closer look at the Gerber files, it looks like some component values and text that should have been on a silk screen made it into the bottom copper layer?

Corby, could you show images of the bare PCBs, top and bottom so that I may compare them? For example, there's a "PPS" text that fused with one of the traces on the bottom layer. It doesn't seem to cause any shorts, but doesn't instill a lot of confidence either.

[ch_scr]

[...]
One parting comment, there was a mixer test done by I think it was NIST for NASA, or maybe the other way around, and a guy used the B-E junction of common transistors for the diode ring.  They then used 5:1 and inversely connected transformers and they claimed with tables and pretty graphs that the phase noise of their mixer whipped all the MCL versions.  I don't remember if the SBL-1 or TUF-3, etc were in that test, also don't know if it matters that much but since you did such a great job bringing the DMTD back to the masses here I thought I would mention it.
[...]
Jerry

This seems at least related https://tf.nist.gov/general/pdf/2554.pdf

[tkamiya]

Thinkfat,

That's probably because an older version of (still available) Express PCB does not do screen printing on bottom layer.  New version of the software does. 

Jerry,

Some versions of 11801 has full adjustability via EFC.  Some does 5Hz.  Some does 1Hz.  One for HP5071A (which I have) does 10Hz but it is pain to use EFC as change rate is too fast.

[notfaded1]

Thinkfat,

That's probably because an older version of (still available) Express PCB does not do screen printing on bottom layer.  New version of the software does. 

Jerry,

Some versions of 11801 has full adjustability via EFC.  Some does 5Hz.  Some does 1Hz.  One for HP5071A (which I have) does 10Hz but it is pain to use EFC as change rate is too fast.

So does it make more sense to just use a 10 turn pot to adjust the frequency offset?  Or possibly just find a good OCXO that can be adjusted with it's own built in adj?

Bill

[tkamiya]

I find 10 turns to be still a bit too fast on some, especially when adjustable range is more than 1Hz.  In those cases, I do corse-fine arrangement with multi-turns.  I've tried several arrangements for the latter but none seem to work too well.  Someone suggested putting a second VR on ground side of first.  I'll have to try that next.

[notfaded1]

I've got some really nice Bourns 10 turn pots.  So you're suggesting using two instead of one then?

Bill

[tkamiya]

Depends on what you got for OCXO and its range of EFC.  If it moves more than few Hz, I'd go with two.  Since 10 turns are wire wound, values jump.  It will be very finicky to do with just one and have an effective control.  You could, of course, breadboard it and see how you like it.

[notfaded1]

10 Hz may be more difficult but it sounds like 1 Hz using the built in coarse control on 10811 would be pretty ideal without needing anything else right?  Going for 10 Hz may be a little more tricky but would neat to try.  I've got a literal boatload of different OCXO's many with built in the voltage references.  I have a box of new 10811-60111 and recently just bought one of the original HP counters that used the OCXO boards I have.  Interesting thing... I have large collection of older counters all with Nixie tube displays (because I love the classic neon display technology).  These might actually make a good TIC for a DMTD and would look really cool at the same time.  Attached are pics of the counter... I haven't taken it out of the box yet.  The 10811-60111's look like in attached picture.

Attached are two of my favorites of these because of the tubes they use.  WE LOVE NEON!
https://lh3.googleusercontent.com/-2n0QFSqoqyY/Wm2zTWQi09I/AAAAAAAABjc/-oOk1B6I7SAzaxgsg9NmmfFH47WKP9nQQCLcBGAs/s1600/People%2BLike%2BNeon%2B600%2Bx%2B338.gif
This is gif of a B-7971 tube clock I have called the MOD-SIX.

Bill

[tkamiya]

Yes.  With 1Hz span, one 10-turn is good.  Still touchy but do-able.  Ones that were originally designed to be used in PLL circuit, has 10Hz and 5Hz spans.  Be mindful that initial tuning will be a bear as opening the cabinet to adjust alone will cause a good shift in frequency.  Devising a way to do it through a hole from outside will be ideal.

Colby tested 10MHz shift and he says it is sufficiently stable, so that's what I'm going to use.  My current plan is to have a set of offsets with a selection switch.  I bought mercury wetted reed relay for this.  By always having heater running, it should only take few minutes to settle down to new setting.  Once everything is setup, I'm also going to try using PLL signal generator to see how much difference it actually makes.  My understanding is this is entirely usable.

I grew up using nixie.  As such, I'm not that fond of it myself, but I am aware they are quite popular.  My preference is LED.

Another thing I'm not sure about right now, along with DUT, I need something going into channel A and this needs to be a stable 10MHz.  I don't have anything that good at the moment.  That is going to be a problem....

I like what you did with a steel case.  Is that electrical junction box?  How did you machine it?

[Mrt12]

Another question @Corby.
I see that you have connected the ECL outputs of the MC1650 to the mixer with DC coupling. What happens if you disconnect the input signal at the clock input? I guess Q is low and Qbar is high, so there must be a DC current flowing through the mixer. Doesn't this cause any problems?

[5065AGuru]

The current in the mixer dynamic or static should have the same peak value so will not cause a problem.
Just got three more boards with the updated layout.
I don't see a "PPS" text that fused with one of the traces.
(my original was modified by chuckb so that's where it came from!)
Since I assume that they made the boards with the Gerber file they sent me that should not be an issue.
Top and bottom Pix attached.
If you stay at one offset then just use the mechanical adjust to get you the offset and the EFC for a fine tweak. You don't need ultimate precision for the offset frequency, you just need it stable. I usually end up running at 1.0005Hz or so.
Don't really know it the EFC on an FTS 1200 can pull it 1Hz, the one I use for the offset won't tune to 5Mhz but it will tune to 4.999999! So that's what I use. There is no mechanical adjust on the FTS 1200, just an external EFC input pin.

Cheers,

Corby

[tkamiya]

Corby,

Can we please have a "stuffing chart" for the bottom layer?

Also, on top chart, I see you have naked rounds right below the metal cans of DBM.  That'll be an issue, right?

Question:
There is DUT and there is reference.  (Not the offset input)
For a given DUT, what is the requirement of reference?  10 times better as usual?  So it'll be an issue if say, I want to compare 11801 and all 3 oscillators are 11801, right?

ps.
I just searched on "DMTD" on eBay....  the first item that showed up was a sex toy.

[chuckb]

Having Gerber files would still be better. 3 boards done by Aisler will cost significantly less.

Here is what Express PCB sent to me. Hope it works for you!
...
    .CSV = pick and place

Took a closer look at the Gerber files, it looks like some component values and text that should have been on a silk screen made it into the bottom copper layer?

Corby, could you show images of the bare PCBs, top and bottom so that I may compare them? For example, there's a "PPS" text that fused with one of the traces on the bottom layer. It doesn't seem to cause any shorts, but doesn't instill a lot of confidence either.

When I did the "D" version of the PCB last week I added the component values to the silkscreen on the top side and I added the component value text into the copper ground plane on the back side. This was deliberate. All the bottom side text looks backwards in the Express PCB software because it's an X-Ray view of the pcb. Yes, the first P in PPS overlays a 5V power trace but it will not affect the electrical performance.

I also moved a 51 ohm resistor from between the mixers closer to the center SMA connector because I was concerned about clearance to the mixer case.
ChuckB
 

[thinkfat]

Does anyone know if these mixers (ADE-1, SBL-1 in particular) are symmetric with regards to the LO and RF inputs? Are these interchangeable? That would allow for a very nice, symmetric component placement for the two channels.

[Mrt12]

Does anyone know if these mixers (ADE-1, SBL-1 in particular) are symmetric with regards to the LO and RF inputs? Are these interchangeable? That would allow for a very nice, symmetric component placement for the two channels.

Hi,
I just measured the inductance of the LO and RF inputs of a couple mixers using my HP 4262A.

For ADE-1+: both, LO and RF input, have an inductance of 31.5 uH.
SBL-1X: 10uH for LO, 15uH for IF
SRA-1: both inputs 17.5uH
SRA-3: both inputs 230uH

so, for *most* mixers it looks like the LO and RF inputs are interchangeable, at least when the inductance is considered. Perhaps the turns ratios of the corresponding transformers are not the same, I cannot tell as I didnt want to dismantle my mixers.

[ch_scr]

I have made a layout for the board. It's intended for either powering from µPowerDirect A324R (3W) or Traco TEN4-2422 (4W), whichever makes the cut
(you guessed it, parts bin had both. 3W might be on the edge tho).
It's intended to be milled as 2-sided PCB, the yellow inner layer shows placement of wire links. This is done so a groundplane can be on one side.
I have 4 seperate local regulation +-6V for both inputs (1,2) the offset input (3) and both IF amps (4) with LM337 / LM317 SO-8.
I suppose this is more usefull as a starting point then to be made as a direct copy.

[notfaded1]

I just had a thought for the 5MHz Reference I could use the BVA.  I'd like to figure out a 5MHz and 10MHz setup.  Another question.  If you had two of these setup could you hook it up so you could do three corner hat measurements?  Would you use the same reference or same offset reference in a case like this?  Obviously I'd like to start with one that works but thinking about how you would hook up for three corner hat measurements?  I'm going to learn the other software you're using Corby.  I've used Stable32 and timelab.  I'm not as familiar with your other tool.

Regards,

Bill