Using the Racal-Dana 1992 as an external reference for the Siglent SDG1025 - Page 1
Forum section: electronics / testgear

author: Aaron D. Parks
author_rank: Contributor
timestamp: September 15, 2014, 02:16:24 pm
content: I wanted to use the 10 MHz output from a Racal Dana 1992 counter as an external reference for a Siglent SDG1025 function generator, but the output level wasn't high enough, so I made a cute little amplifier.It's a simple two-transistor affair: a common-emitter stage for voltage gain followed by an emitter follower. I had some boards made up and used a tiny little aluminum extrusion case from Hammond. I actually wanted to use their smallest, but it wouldn't have fit two BNC connectors and the power jack.I was a little surprised that the input impedance of the external reference port on the SDG1025 didn't seem to be 50 ohms, but maybe that's normal?I did run into what I think is a firmware bug in the SDG1025. After setting the clock source to external, restarting it has it using the internal clock again even though the setting is saved and still says "external".Toggling the clock source to internal and back to external works to get it using the external reference again, though.This is my second video of this type, so I'd be interested to know what you think of it.

author: MarkPalmer
author_rank: Regular Contributor
timestamp: September 15, 2014, 02:32:33 pm
content: It does seem like a firmware bug in the Siglent, would be kind of a pain to have to go through those menu settings every time at power up to use the external reference. I do this same thing with several of my pieces of synthesized equipment, slave their 10 MHz references from pieces of equipment that have crystal ovens under power 24/7. The older HP 10 MHz oscillators usually have enough drive to slave a couple of other pieces of gear. Good video-Mark-

author: kwass
author_rank: Frequent Contributor
timestamp: September 15, 2014, 03:27:14 pm
content: I do exactly the same thing as you and built a similar interface box (using just a 74HC14 chip as the buffer) between my Racal 1992 and the Siglent 1025. I also encountered the same firmware bug and report it here:https://www.eevblog.com/forum/testgear/siglent-technical-support-join-in-eevblog/msg498980/#msg498980Nice video!

author: Aaron D. Parks
author_rank: Contributor
timestamp: September 15, 2014, 05:20:03 pm
content: Thanks for the kind words about the video!Yeah, the firmware bug is an annoyance. Hopefully they'll get it fixed up soon. I don't use the external reference all the time. If I know I'll be using it for a while, I just leave the machine powered on.The 74HC14 is a neat solution. I wouldn't have thought of that. Cool! Did you have to parallel several of the inverters to drive the SDG1025?

author: kwass
author_rank: Frequent Contributor
timestamp: September 15, 2014, 05:57:45 pm
content: Quote from: Aaron D. Parks on September 15, 2014, 05:20:03 pmExactly. I needed 3 of them in parallel but could have used all 6 if I didn't care about the current draw. But I run it off batteries inside the interface box so current consumption is important. I don't use the external input all the time either, but mostly because it takes the ovenized oscillator in Racal 1992 30 minutes to warm up, before then it it's as far off as the internal oscillator in the SDG1025.As a compromise alternative I made a different box (also battery powered) that uses a TCXO:http://www.ebay.com/itm/371068259913?_trksid=p2060778.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITThis one can drive the SDG1025 directly and can be carefully tweaked to be better than 0.1ppm. This gives pretty good accuracy with zero warmup time.

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2014, 01:35:35 am
content: That looks like a simple enough solution Aaron. I have a 1992 as well but probably would have modified the reference output inside the counter so it could be connected directly to the Siglent without another external box. I have considered doing something similar with a simple GPSDO installed inside the counter.I am always on the lookout for new printed circuit board sources and I may give dirtypcbs.com a try but where did you find that clever little enclosure? The way the printed circuit board fits into the extruded aluminum rails reminds me of how the Tektronix S series sampling heads are constructed.

author: Aaron D. Parks
author_rank: Contributor
timestamp: September 16, 2014, 03:16:30 am
content: Quote from: kwass on September 15, 2014, 05:57:45 pmNice. I imagine that type of setup could run quite a while on a modest battery source. I leave the hard power switch on the RD 1992 on and use the standby button instead. It seems to keep the oven on that way. Anyway, the case is warm to the touch and it seems to stabilize faster.

author: Aaron D. Parks
author_rank: Contributor
timestamp: September 16, 2014, 03:21:48 am
content: Quote from: David Hess on September 16, 2014, 01:35:35 amIt's from Hammond Manufacturing, their 1455 series. It's also available with plastic end caps. There are two others that look like they use the same extrusion, but have die cast end caps: 1457 (water proof) and 1457 E (EMI gaskets).I think that both Digi-Key and Mouser carry them.

author: BillWojo
author_rank: Regular Contributor
timestamp: September 16, 2014, 04:15:41 am
content: Hi Aaron, very nice video. Thanks for the heads up on the enclosure, I have seen stuff packaged like that but didn't know they could be purchased so readily. I'll make a note about them.ThanksBillWojo

author: Vgkid
author_rank: Super Contributor
timestamp: September 16, 2014, 04:36:16 am
content: your video is actually really well done.

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2014, 04:50:04 am
content: Quote from: Aaron D. Parks on September 16, 2014, 03:21:48 amThanks for this. They are close to exactly what I have been looking for.And here I was thinking of Hammond as a transformer manufacturer. No wonder I missed them.

author: timb
author_rank: Super Contributor
timestamp: September 16, 2014, 12:24:35 pm
content: Quote from: Vgkid on September 16, 2014, 04:36:16 amSeriously! Count me impressed and subscribed!Question: What software were you using to do the 3D mockup of the case inside the enclosure? It looked very nice.One thing I love about Hammond is they provide mechanically accurate STEP and IGES files for *all* their enclosures. (By that I mean every size variant of every style.) Free to download, with no hassle, right from the product pages.Right now I use a combination of FreeCAD and SketchUp, but it's a bit of a pain. (I've got to convert the IGES/Step files in FreeCAD, readjust the scale, attempt to export them in Collada DAE format, which sometimes works but often doesn't. If it doesn't I have to save it as a VRML file and use another utility to convert to DAE. Then import to Sketchup, adjust the scale some more... Then I have to do the same with my PCB model, which DipTrace can export as VRML or STEP.) Okay, so "bit" was understating things... It's just a huge pain! So, I'm in the market for some new 3D cad software.Sent from my Smartphone

author: Aaron D. Parks
author_rank: Contributor
timestamp: September 16, 2014, 12:54:10 pm
content: Quote from: timb on September 16, 2014, 12:24:35 pmThank you! And thanks to everyone else who had nice things to say about the video!Quote from: timb on September 16, 2014, 12:24:35 pmAutoCAD 2014. Once you get the hang of it, it's pretty handy. The price, though...After finishing the model, it's easy to create sheets with dimensions and such for each part that needs to be made or modified.It doesn't import all of the 3D formats I'd like. I use Inventor Fusion (free) for converting and small tweaks. Fusion has some other neat features, too.Quote from: timb on September 16, 2014, 12:24:35 pmYes! And they have a wide range, too, from tiny up to stuff you could play hide-and-seek in.

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2014, 04:09:32 pm
content: Quote from: timb on September 16, 2014, 12:24:35 pmI noticed the same thing looking through the Hammond web site. It is refreshing to have detailed documentation, lots of high resolution photos, and no non-disclosure agreements or click-throughs.

author: robrenz
author_rank: Super Contributor
timestamp: September 16, 2014, 04:38:56 pm
content: Very nice video indeed