DMTD board

[5065AGuru]

I'll get into more detail on the offset oscillator in the tutorial post but you want to have an offset oscillator that has very good short term stability.
I use an FTS 1200 with a 1HZ offset at 5 Mhz.
The 10811 at 10Mhz can be used also with a 1HZ offset or a 10Hz offset.
I almost never use a 10Hz offset but you can do it.

Corby

[chuckb]

Corby
Thanks for the design. I will be building one. I pulled ten Efratom FRK Rbs from surplussed VLF Navigation equipment many years ago. 

On the schematic the output pairs of the MC1650 chips are terminated with a 51 ohm and a 220 res network. Three of the four pairs use 0.1u filtering cap. The 2nd from the top uses 0.01u caps. Is this correct?

The lowpass filter after the DBM has a RLC filter. Are those 0.1u caps C0G dielectric? I have had distortion issues with X7R caps used in filters in the past. Because of their nonlinear characteristics.

My favorite C0G cap right now is TDK. Other brands can have issues.
https://www.eevblog.com/forum/metrology/film-and-ceramic-capacitor-leakage-current/msg3190618/#msg3190618

[5065AGuru]

chuckB,

Corrected the schematic!

I used the bypass .1 caps for those 4 also but I did match them. Probably would be good to change them to film or other type.

Had to add the expressPCB file as a ZIP file. Once unzipped you can load it into the  express PCB program to inspect it. From there you can order boards from them, 3 boards for around $78.00 with shipping.

Cheers,

[tkamiya]

Two 0.01 C0G....  are they the one at positive input of LT1008?

4007pf COG, they are at output of DBM, correct?

Power to MC1650L, positive side is going through an inductor and bypassed by two caps, where as negative side isn't.  Is this on purpose?

[5065AGuru]

Yes,

Yes the only two .01uf on the board are at the input pins of the LT1008.
Yes the 4700 are across the output pins of the DBM.
The positive into the 165X is bypassed by a .1uf ceramic and a 10uf Tantalum.
The minus into the 165X only has the .1uf and no inductor.

Cheers,

Corby

[chuckb]

Corrected the schematic!
I used the bypass .1 caps for those 4 also but I did match them. Probably would be good to change them to film or other type.

Just tried to add the expressPCB file but it won't take the .pcb file extension anyone know how to post the file?

Looks like the system will accept an attached ZIP file

[chuckb]

chuckB,

Corrected the schematic!

I used the bypass .1 caps for those 4 also but I did match them. Probably would be good to change them to film or other type.

Had to add the expressPCB file as a ZIP file. Once unzipped you can load it into the  express PCB program to inspect it. From there you can order boards from them, 3 boards for around $60.00

Cheers,

I added part Values onto the PCB to help me with assembly. I took a guess for the 68 ohm terminations on the output HEX Buffers. Let me know if I messed anything up.

[thinkfat]

Going by the currently attached schematic, did you intend to just short all the HCT14 outputs together? There should be a small series resistor after each of the inverters before you link them to OUTA and OUTB, no?

[Mrt12]

Going by the currently attached schematic, did you intend to just short all the HCT14 outputs together? There should be a small series resistor after each of the inverters before you link them to OUTA and OUTB, no?

I agree to that. Besides that, the output impedance of  a HC14 is not 50 Ohm but maybe around 30 Ohm or so. If you short 5 outputs together, this results in perhaps 6 Ohms output impedance.
It would be better to use approx. 220 Ohms series resistors at each output. This would result in a total output impedance of 250 Ohms for each output, and then 5 of them im parallel brings you to 50 Ohms.

[thinkfat]

What I'm more worried about is that the top mosfet of one output and the bottom mosfet of another output might be both conducting during a transition. That will give quite some spikes on the supply rail.

[Mrt12]

What I'm more worried about is that the top mosfet of one output and the bottom mosfet of another output might be both conducting during a transition. That will give quite some spikes on the supply rail.

I would not worry too much about this. In my GPSDO I used a 74ACT541MTC with paralleled outputs and that works fine.

[Mrt12]

Corby,
now I looked at the schematics. Thank you.
I saw that you actually use the differential outputs of the ECL comparators to drive the two transformes inside the mixers in a differential manner. This is indeed very interesting! are those internal connections of the SBL-1 documented somewhere or did you find it yourself? besides that, the Minicircuits datasheet reads that the ground pins need to be connected externally, which you don't (because you use the primary windings of the transformers of the LO and RF inputs in the differential configuration). Do you know whether the mixer's isolation or other characteristics degrade somehow in this configuration?

I would like to use ADE-1+ or ADE-2+ in my DMTD, and for these, there is, similar to the SBL-1, no official document from miniricuits where I can see the actual connections of the internal transformers. However, here

https://www.on1bes.be/sdr_up_conv_v1.0_ade1_125_en.html

I found a schematic where the internal connections are visible, so it appears as if this mixer could be used in the same way as you do: input the RF at pins 3 and 4, and LO at 1 and 6. What do you think?

Further I thought about using a PECL or LVPECL comparator to drive the mixer inputs. Or would it even work with an LVDS line driver? Just directly connect the differential outputs of the driver to the mixer transformers.
For instance, would an LMH7220 be usable?

[thinkfat]

Corby,
now I looked at the schematics. Thank you.
I saw that you actually use the differential outputs of the ECL comparators to drive the two transformes inside the mixers in a differential manner. This is indeed very interesting! are those internal connections of the SBL-1 documented somewhere or did you find it yourself? besides that, the Minicircuits datasheet reads that the ground pins need to be connected externally, which you don't (because you use the primary windings of the transformers of the LO and RF inputs in the differential configuration). Do you know whether the mixer's isolation or other characteristics degrade somehow in this configuration?

I would like to use ADE-1+ or ADE-2+ in my DMTD, and for these, there is, similar to the SBL-1, no official document from miniricuits where I can see the actual connections of the internal transformers. However, here

https://www.on1bes.be/sdr_up_conv_v1.0_ade1_125_en.html

I found a schematic where the internal connections are visible, so it appears as if this mixer could be used in the same way as you do: input the RF at pins 3 and 4, and LO at 1 and 6. What do you think?

Further I thought about using a PECL or LVPECL comparator to drive the mixer inputs. Or would it even work with an LVDS line driver? Just directly connect the differential outputs of the driver to the mixer transformers.

The main difference between the ADE-1 and the SBL-1 seems that ADE-1 just bonds out the center tap of the secondary winding while the SBL-1 has the individual secondary transformer coils available.

[ch_scr]

View inside "HPF-505, SRA-1, SBL-1, IE-500" http://www.qrp4u.de/docs/en/Components/index.htm

[Mrt12]

The main difference between the ADE-1 and the SBL-1 seems that ADE-1 just bonds out the center tap of the secondary winding while the SBL-1 has the individual secondary transformer coils available.

Indeed. But that would be not much of a problem because these centre taps are connected together anyways, are they.
What could be the reason that Minicircuits does not provide these official pinouts but instead labels all of these pins  as ground?

[chuckb]

Updated the unofficial schematic parts layout. I had the polarity of a 10u tant backwards in the lower left corner.

[chuckb]

Now the board passes DRC for Express PCB

[thinkfat]

Corby, any indication how the design would perform with just +/- 5V power rails? It will impact the LT1008 and the LM311 of course, but is it relevant?

[5065AGuru]

Thinkfat,

Original design ran with +5.0 -5.2 and +- 15VDC.
I ran the prototype that way except for +- 12VDC as I had a packaged module of that voltage.
I also ran it a -5.0 to see what happened and performance looked OK.
I haven't considered trying it at +- 5 only.

The current draws are 10mA on the +- 12, 30mA on the +5 and 200mA on the -5.
So you could use a 5V regulator off the +12 to get the +5.
The same for the -5 if your +12 supply would take the load. You would need a heat sink!

Cheers,

Corby

[5065AGuru]

On my other dual mixer setups I use a dual monostable like the 74C221 to drive "heart beat" LEDS. One for the start channel and one for the stop.
The monitor outputs on the board are provided to do that. I usually just wire it up on a perf board and select the one shots time to give a good visible pulse. It's handy as it will easily show if you are missing an input.
I use the long threaded SMAs to mount the card to a front panel and run the output pulses to BNCs on the front panel.

Corby

[Mrt12]

Dear colleagues

I investigated a bit more concerning those MC1650 and MC1651 devices because I wondered whether there is a more modern alternative to them.
In this document here

https://cddis.nasa.gov/lw11/docs/slrpap1.pdf

on pages 2 and 3, there is a recommended circuit which shows how to AC couple a sine into an ECL gate. The gate used in this example is an MC10EL16, which, fortunately, is still available and even sold by Mouser.
The authors of this document claim that the minimum required input amplitude is around 800mVpp, which is around 1 to 2 dBm into 50 ohms.
However I don't know whether it will be a problem if a higher amplitude would be used.
However to me it looks like this device could be used alternatively to the MC1651. What do you guys think?

Yesterday evening I did a simple test with an ADE-1+ mixer, and connected two square waves to its input. Indeed it works just as fine as with sines, and also the LTSpice simulation confirms this. So I think this is a really smart idea Corby had there, because it basically makes the DMTD completely independent of the input amplitude!

(Next question would then be whether this approach is also usable for phase noise measurement.)

[tkamiya]

I was getting ready to order some boards and noticed 68 ohm register at the output exists on the board but not on circuit diagram.  Which one represents the latest design?  (I'm so excited!)

By the way....  3 for $51 pricing does not appear to include solder masking or silk screening.  With solder masking the order is +20 dollars  Am I doing this wrong??

[chuckb]

There are two options for the PCB assemblies. I did the $70 version with solder mask because I know how bad my soldering is.

[5065AGuru]

Taka,

Nice catch,

added the 0utput resistors on the schematic.

With the solder mask (recommended!) and top silk screen parts total came to $79.00 including the shipping.

Cheers,

Corby

[tkamiya]

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?