10MHz distribution in lab - Page 1
Forum section: electronics / testgear

author: Jester
author_rank: Frequent Contributor
timestamp: December 12, 2016, 06:02:58 pm
content: I have a Rubidium standard FE-5650 on order and would like to distribute the signal to several instruments so they are all marching to the same drum as well as improve their accuracy. The FE-5650 outputs 0.5VrmsInstruments: Min Sig Level In Sig level outSiglent SSA3000x 100mV 220mVRacal-Dana 1992 counter 100mV 600mVMaconi 2022C 1000mV n/aHP 33120A (If I ever find the optional ext input board)Option A is to daisy chain them in the order shown above, and if the 600mV is too low for the Marconi, make a small 2x amplifier using a LM7171 or similar.Option B is to purchase a 75Ohm video distribution amplifier and tweak the output impedance and then distribute one per instrumentI have read comments about introducing ground loops, so some distribution amplifiers are transformer coupled, not sure if this is necessary?Seems many of the video amplifiers are specified with a 50MHz minimum frequency, not sure if they actually have some sort of LPF that would be a problem when distributing 10MHz?If I do cobble together a x2 amplifier, do you see any issue with making this on a simple proto board without a proper ground plane etc?

author: DaJMasta
author_rank: Super Contributor
timestamp: December 12, 2016, 06:42:26 pm
content: Sine or square wave output?If it's square, it's incredibly easy to make your own distribution amp - just need some ttl schmitt triggers and some BNCs, basically. I've got a few boards made for a 4 way distribution amp that fit inside my reference, one of those cheaper GPSDOs. Need to build one up to see how well my 10MHz square to sine filter works, but the square wave outputs have been working great for weeks now in my GPSDO.Did some testing with a decent quality opamp to just pass through the sine wave directly from the oscillator inside and it works fine, but decent opamps are more expensive and at least where i was tapping the signal off of, there were square and sine options available.There's the video distribution amps that people use and a couple that have been documented on this forum, then there's some slightly more expensive amps designed for 10MHz references available, then there's the insanely expensive options from some of the big manufacturers... but my little dollar board with 70 cents of parts and like $9 in BNCs has done a great job for me so far.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 12, 2016, 06:46:15 pm
content: If you go in-out as you've shown, all your equipment has to be turned on to get the reference signal through the chain. Also, each piece of equipment will add noise and jitter to the reference. Not recommended!Check the impedance of the external reference input for your equipment. These inputs are often much higher than 50 ohms so that you can just daisy-chain a single cable from the reference to all the equipment by using a BNC T connector at each piece of equipment. A terminator at the end of the line is probably a good idea unless one of the pieces of equipment has a 50 ohm input in which case, that can be the last piece on the chain.A distribution amplifier is a good idea, not just for distributing the reference signal, but also for providing a buffered reference signal for various experiments. You probably don't need to connect each piece of equipment separately to the amp, but you could. Ground loops are a fact of life that you will fight with from time to time. Whether you use a daisy-chain or star-connected arrangement, all the grounds are still connected together.Remember that when you change the output impedance from 75 to 50 ohms, you might have to derate the output. If it had eight 75 ohm outputs, it might only be able to drive five 50 ohm outputs before it overloads.AVIDEOdistribution amplifier likely has a frequency response from DC, or very low, up to 10 or even 50 MHz. AnRFdistribution amplifier often starts at 50 MHz and can go up to 1 GHz. Don't buy the wrong one! You can try building an amp on a protoboard, but external interference might be a problem. For similar situations, I took a metal cookie tin and mounted BNC connectors on it so I can put the protoboard inside the box.Ed

author: Jester
author_rank: Frequent Contributor
timestamp: January 17, 2017, 01:30:25 am
content: Now that I have my Rubidium and GPSDO sources up and running I need to distribute the 10MHz sinewave signal.If you had to choose between these two which one would you use?Option 1http://www.ebay.com/itm/1-to-8-BNC-Composite-Video-Splitter-Distribution-Amplifier-CCTV-Surveillance-/191442786349?hash=item2c92e1182d:g:Em4AAOSw2XFUhrDWand hopefully tweak the 75to 50Option 2 DA1-4HLhttp://www.g4hup.com/DA/DA1_4.htmOr if neither, why not and what would you recommend?

author: tautech
author_rank: Super Contributor
timestamp: January 17, 2017, 01:59:12 am
content: If you can get away with just 4 outputs then option 2. Why ? It's made just for your needs.

author: torch
author_rank: Frequent Contributor
timestamp: January 17, 2017, 03:00:26 am
content: Quote from: Jester on January 17, 2017, 01:30:25 amThe eBay auction listed specifies a bandwidth of 50Hz-5.5MHz.

author: Johncanfield
author_rank: Regular Contributor
timestamp: January 17, 2017, 03:00:41 am
content: I hacked an Extron ADA 4 300MX from eBay for a distribution box ($25 with shipping.) Basically you replace the 75 ohm surface mounts with 50 ohm smd's, easy hack.

author: Jester
author_rank: Frequent Contributor
timestamp: January 17, 2017, 04:20:42 am
content: Quote from: torch on January 17, 2017, 03:00:26 amGood catch, perhaps this one:http://www.ebay.com/itm/272254151342?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITBW=350MHz, specifictions attached

author: cdev
author_rank: Super Contributor
timestamp: January 17, 2017, 05:11:39 am
content: A video distribution amp, maybe with some tweaking to improve the "low end response"Making sure to terminate the unused outputs sounds like it would be easy to do. For transformers/galvanic isolation use a balun core wired as a simple transformer. The core material likely isnt super critical.

author: lmester
author_rank: Regular Contributor
timestamp: January 17, 2017, 06:21:49 am
content: I just recently finished doing this. I got a cheap sigma electronics vda26 six output video distribution amplifier from Ebay. Swapped the 75 ohm resistors with 50 ohm. The vda-26 has adjustable gain. Also, my GPSDO has square wave output. I decided to run it through a filter to produce a sine output. Used sigma electronics video amps are really cheap. I bought a lot of two for $25 total including shipping! A nice piece of equipment. Nice metal enclosure with built in power supply. There are many different versions of sigma electronics video amps for sale. Many are made with one or more vda-21 boards in an enclosure. Each board adding six outputs.Attached is the spec sheet for this unit.

author: TheSteve
author_rank: Unknown
timestamp: January 17, 2017, 06:30:02 am
content: The VDA-26 is priced right but it would be nice to have truly isolated outputs.

author: Bryan
author_rank: Frequent Contributor
timestamp: January 17, 2017, 07:01:08 am
content: Schematics are available if you didn't want to go the kit route. Isolated.https://www.tapr.org/kits_tadd-1.html] https://www.tapr.org/kits_tadd-1.html

author: lmester
author_rank: Regular Contributor
timestamp: January 17, 2017, 03:10:36 pm
content: Quote from: TheSteve on January 17, 2017, 06:30:02 amYes, it's not isolated. I had thought of adding transformers to isolate the outputs. Unfortunately, the BNC connectors are tightly packed on a PC board. It would be a job to get their grounds all isolated. I decided to try it without isolation. So far I've had no problems. My equipment is all powered from Wiremold plug strip. All from a single branch circuit with a common ground. If you want to modify an existing unit for isolated outputs the VDA-26 is probably not the best choice.I did a lot of research on 10MHz distribution. A good source of information is the time nuts mailing list.https://www.febo.com/mailman/listinfo/time-nuts. Archives of the list are available. IMHO if you're doing precesion time nuts type measurements you need an amplifier designed for this task. If you just need a good reference frequency for some instruments a surplus video amplifier will be fine.I almost bought one of the TADD-1 kits from TAPR. It's designed for 10MHz distribution but was a little expensive for me. If you don't have a problem with $100 the TADD-1 would be a good choice. It has good reviews.Here are some pictures of the VDA board. Also, my latest project that's using the 10MHz reference. Adjusting the rate of a quartz clock.

author: bingo600
author_rank: Super Contributor
timestamp: January 17, 2017, 04:17:50 pm
content: I'm using a video distamp too , but had to put a 3dB attenuator on the input.Else the signal from my Tbolt was distorted.I have a Racal.9480 40 (5x8) Chan distamp, that i ought to get in use , it can either give 10Mhz via the OCXO , or take 10Mhz on the input and distribute on all 40 chans./Bingo

author: jpb
author_rank: Super Contributor
timestamp: January 17, 2017, 06:30:16 pm
content: Quote from: lmester on January 17, 2017, 03:10:36 pmThe BNC connectors look very closely spaced in those photos - I would have thought it would be tricky attaching and removing cables.

author: lmester
author_rank: Regular Contributor
timestamp: January 17, 2017, 07:27:57 pm
content: Quote from: jpb on January 17, 2017, 06:30:16 pmSo tight that they make a tool for it...

author: mmagin
author_rank: Frequent Contributor
timestamp: January 17, 2017, 08:15:41 pm
content: Another inexpensive option (I have one of these and it works fine) using common MMIC ICs:http://www.downeastmicrowave.com/product-p/10-4ck.htm(kit form, SMT soldering required)http://www.downeastmicrowave.com/product-p/10-4.htm(assembled)(Requires a reasonably clean 11-18V 200mA power supply)(Edit, also, looks like you can get the board-only or the board and the board-mounted components only, if you want to DIY more of it and are feeling cheap:http://www.downeastmicrowave.com/category-s/1833.htm)

author: G0HZU
author_rank: Super Contributor
timestamp: January 17, 2017, 10:08:36 pm
content: QuoteFrom what I've seen those FE5650A Rb units often produce high spurious levels. eg lots of spurs at about -80dBc to -90dBc a few kHz from the 10MHz carrier. If so, I'm not sure it would be a good idea to use it as a 10MHz reference for the LO synthesiser in a 3GHz spectrum analyser or even a 1GHz signal generator. I think some Rb units use a DDS to generate the 10MHz output and this produces lots of spurious terms. Have you checked it to see if it is clean enough to use as a reference for an LO running up at several GHz?

author: Spwhite
author_rank: Contributor
timestamp: January 18, 2017, 01:34:07 am
content: Quote from: Johncanfield on January 17, 2017, 03:00:41 amDitto on this. I have the same unit, stuffed in my Bulova PCOXO right into the same case, using the built in power supply. Works like a champ in my lab.

author: pauln
author_rank: Contributor
timestamp: January 19, 2017, 12:27:44 am
content: DEMI have a built or kit solution. I use one board with 4 outlets, but you can add to if required. Adds buffer, isolation and filtering.http://www.downeastmicrowave.com/category-s/1833.htm

author: Bryan
author_rank: Frequent Contributor
timestamp: January 19, 2017, 09:21:06 pm
content: QuoteSchematics are available so one could roll there own out cheaper, but sourcing components, build time, PCB and yes sometimes easier to buy the kit.