Author Topic: DMTD board (Read 89481 times)

chuckb · « **Reply #100 on:** October 13, 2020, 09:06:33 pm »

Make sure to space the mixer slightly off the PCB when soldering it. If you don't have a slight gap it's easy to add to much solder and it will flow and short to the case. I know this from experience. Somebody makes a dedicated spacer for this but you could use a folded business card to hold 0.030" gap while you solder.
I ordered the pcbs but some of the parts are coming in from china so it will be a few weeks yet.

rubidium · « **Reply #101 on:** October 13, 2020, 09:23:06 pm »

Quote from: tkamiya on October 13, 2020, 09:00:43 pm

I have a question for the group about offset oscillators.

What type of precision/accuracy/stability do I need? Granted better is.... BETTER but having have to have slight offset to normalized frequencies provide extra challenges. Some products such as "Small DMTD" by Mr. Riley uses one chip DDS source with an external reference.

I can easily tune HP10811 off 1Hz by coarse tuning, but any more than 1Hz, I have good possibility of pulling it too far for a stable operation. I plan to do 0.1 second reading, which requires 10x output per second, which in turn requires 10Hz offset. I don't know of any good way to achieve this. Given input splits and goes to both mixers, theory says unless extreme, changes doesn't matter as much. It goes on to explain, such is an advantage of dual mixer scheme compared to single mixer.

SO... is something like well behaving HP5644A/B sufficient? Anyone have comment?

This is tied to a more general question that I have. What happens to the stability of any good crystal oscillator, nominally rated for frequency F if you tune it to F +/- dF, assuming dF is within the oscillator's EFC range?

thinkfat · « **Reply #102 on:** October 13, 2020, 09:51:46 pm »

Might be a good reason/opportunity to buy one of Leo Bodnars mini precision frequency standards.

tkamiya · « **Reply #103 on:** October 13, 2020, 11:21:22 pm »

Once I have DMTD working with a good reference, I will be able to measure that.

5065AGuru · « **Reply #104 on:** October 14, 2020, 12:36:12 am »

Taka,

The HP10811 is specified to tune + - 10Hz so I don't see a problem there!
I'll see if I can measure a 10811 stability at +10 and -10Hz this weekend.
Remember you can use either the + or the - offset, whichever you can reach.
My offset oscillator is very stable and I use a 1Hz offset. (4.999999 MHz) It runs 24/7.
When I start the DMTD tutorial post (soon) one of the things covered will be the offset oscillator.

Cheers,

Corby

tkamiya · « **Reply #105 on:** October 14, 2020, 12:41:05 am »

Appreciate it, Corby!

Pipelie · « **Reply #106 on:** October 14, 2020, 08:16:35 am »

I'm new in time-nuts, while I'm looking what's DMTD means,
I found an article that looks promising
design detail, schematic, and test results are all in the article.

A Small Dual Mixer Time Difference (DMTD) Clock Measuring System
http://www.wriley.com/A%20Small%20DMTD%20System.pdf

Pipelie · « **Reply #107 on:** October 14, 2020, 08:21:34 am »

Spec:

FriedLogic · « **Reply #108 on:** October 14, 2020, 12:32:46 pm »

I checked with ExpressPCB, and the cost for 3 boards including delivery, customs, etc. for the UK would be something like $140.
At some point I would like to convert it to KiCad anyway, but for now, are there any gerber files available? I'd like to build at least one of the original ones as a reference.

tkamiya · « **Reply #109 on:** October 14, 2020, 05:33:40 pm »

When finalizing your order, did you pick "mini" PCB spec? There are two choices in "mini" type. One has solder mask and silk screening, and the other doesn't. Also, "mini" are limited to 3 boards. Otherwise, cost will significantly rise.

thinkfat · « **Reply #110 on:** October 14, 2020, 06:00:54 pm »

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

chuckb · « **Reply #111 on:** October 14, 2020, 08:21:30 pm »

Quote from: thinkfat on October 14, 2020, 06:00:54 pm

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

thinkfat · « **Reply #112 on:** October 14, 2020, 08:31:17 pm »

Thanks, the Gerbers look good! KiCADs "GerbView" program can open them just fine.

FriedLogic · « **Reply #113 on:** October 15, 2020, 07:52:11 am »

Quote from: tkamiya on October 14, 2020, 05:33:40 pm

When finalizing your order, did you pick "mini" PCB spec? There are two choices in "mini" type. One has solder mask and silk screening, and the other doesn't. Also, "mini" are limited to 3 boards. Otherwise, cost will significantly rise.

The problem is more the extra costs for international - much higher postage, then clearance fees and VAT.
I feel like a bit of a cheapskate for asking, but it all really adds up.
Anyway, thanks to chuckb for posting them.

thinkfat · « **Reply #114 on:** October 15, 2020, 08:12:12 am »

Aisler quotes around 30€ for 3 boards. Didn't check about the shipping rate, but they're in EU, can't be that much.

5065AGuru · « **Reply #115 on:** October 15, 2020, 05:19:12 pm »

Attached is a PIX showing the bottom mounted surface mount stuff.

starting just to the right of the yellow 100pfd cap the surface mount stuff starts.

47.5K and .1uf PPS cap in parallel then a 1K then 100K and 6800pfd in parallel.

There are also the two not shown, the 4700pf across the output pins of the mixer

The yellow cap is the 100pf.

I'll post a stuffing diagram for the top soon.

Cheers,

Corby

5065AGuru · « **Reply #116 on:** October 15, 2020, 05:37:05 pm »

Taka,

Ran a test of the 10811 at 10HZ offset and it's stability compared to the no offset is just a tiny bit worse but not something that would effect using it as the L.O. in the dual mixer.

Cheers,

Corby

tkamiya · « **Reply #117 on:** October 15, 2020, 05:39:33 pm »

Corby,

I appreciate that very much. Thanks!

I am planning to box together 11801 units to generate 1Hz, 5Hz, and 10Hz. What's the output level required for this DMTD board? I'm guessing it'd be a good idea to follow this with a low phase noise buffer amplifier.

notfaded1 · « **Reply #118 on:** October 15, 2020, 06:26:14 pm »

So what does that mean that 1Hz or 10Hz is better offset? I have a couple 105B's (both contain 10811's) and some loose 10811's. I've been running a 96 hour test of my 5061B as DUT using the 5065 as the reference after it burned in for a couple weeks. Everything is getting better and better. I'm really excited to think the 5065 could be my primary reference vs. running the Cs all the time. Also the 5065 isn't that far off my Cs in frequency and is looking more and more consistent! This morning when I left for work I noticed ADEV had dropped into the 10^14. This is using the 53132 to measure. Next I'm going to try the TURN Dynamic Systems DMTD. I ordered some solid SMA to BNC connectors to convert the TURN DMTD to BNC since I need some longer cables. When I tested some other devices using the TURN (that has SMA connectors) I used semi rigid SMA cables that were factory made by Tek (exactly the same) to an SRO-100 Rb and reference that both had SMA outputs or was forced to use my RF converter kits. Those are the ones where you connect two different RF types together with the center generic connector. I don't think those kits actually are as good as using the factory made ones? Maybe it doesn't matter... idk yet?

Bill

tkamiya · « **Reply #119 on:** October 15, 2020, 06:45:43 pm »

It's not better or worse. Just different purpose.

I have SRS PRS-10, the rubidium standard. One of the characteristic of this unit is a HUMP around 0.5 to 1 second. If I use 1Hz offset, converted signal is 1Hz. That would mean measurement is made once every second. Clearly, that's not fine grained enough to detect something happening a sub-second interval. Raising it to 10Hz offset produces 10Hz. I can measure at 0.1 second interval. That's what I need.

Also, one of my interest is Crystal oscillators, including ovenized ones. Almost all crystal oscillators fall apart, Adev wise, at beyond 300 seconds. At 100 seconds most will start to show problems. I want to be able to measure better than once a second.

As far as I know, de-facto standard for DMTD is 1Hz. This is a special case.

notfaded1 · « **Reply #120 on:** October 15, 2020, 07:56:55 pm »

I like the idea of 10 measurements per second too. That's part of the problem with many counters... you need longer sample periods. That's fine for longer term Rb and Cs measurements.
But it's why we really need this DMTD for shorter sub second measurement periods in additional to obviously being able to get phase data too. Like you said for quartz... it's the shorter Tau we're interested in really.

Bill

tkamiya · « **Reply #121 on:** October 15, 2020, 08:40:41 pm »

I just tried how far I can pull UCT108663. Nominal frequency is 10MHz. On low side, it went to 9,999,995.80. On high side, it went to 10,000,001.38. Benefit of course, is size and simplicity of power supply circuit. I am going to look for modern oscillators and see what's available.

chuckb · « **Reply #122 on:** October 16, 2020, 03:36:41 am »

Just a thought -
When we use a DC voltage to tune an oscillator off frequency the voltage reference can add noise to the RF output signal via the varactor. When you need to reach a specific frequency we just end up with whatever little extra noise is added and we live with it.

For the DMTD reference frequency it does not matter if the oscillator frequency is high or low. So for lowest noise we should pick a minimum tuning voltage. Ground is the lowest noise voltage in the system.

I wonder how much difference it makes.

5065AGuru · « **Reply #123 on:** October 16, 2020, 04:53:58 am »

Taka,

A lot of people use Dual mixers at 10HZ offset. I usually don't but that's just me!

If you need to look at the stability under 1 second then 10Hz is the way to go.

The data files end up being 10X bigger when you go that route.

The simple dual mixer should work from .2V P-P to >6VP-P on the offset input and .1V to >6V P-P on the RF inputs. So for most oscillators just hook them up!

A low noise buffer is not really needed on the offset input, just hook right in.

Cheers,

Corby

5065AGuru · « **Reply #124 on:** October 17, 2020, 06:18:59 pm »

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,

I thought the logo on the top would work so just installed them in opposite directions by that!

Well, that turned out wrong as the mixer output polarity between channels is inverted!

So I'll have to remove a mixer and re-install it in the other orientation.

If your mixers don't have the colored polarity insulator you might want to test them!

Cheers,

Corby


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Author Topic: DMTD board (Read 89481 times)

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