[ASK] Distributing 10 MHz reference signal for T&M equipments. - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: April 28, 2018, 10:00:25 am
content: Can I use this kind of "cheap" video Serial Digital Interface (SDI) splitter/distributor box to distribute the reference 10MHz signal from the GPSDO board ?Example at Aliexpress ->Cheap SDI splitterNo affiliation with seller, just searched for "sdi splitter", choose the one with 4 outputs and sorted by price.Click to enlarge photos.Btw, what is that "Lock" LED indicator for ?

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 10:33:17 am
content: Quote from: BravoV on April 28, 2018, 10:00:25 am"Lock" led could indicate that this is SDI digital regenerator, thus not compatible with 10MHz signal distribution.You shall search not "SDI splitter" but "composite video splitter BNC".Like this random google hit:http://www.thesmarte-mart.com/ProductDetails.asp?ProductCode=SB-3701BNC

author: douardda
author_rank: Regular Contributor
timestamp: April 28, 2018, 10:54:08 am
content: Quote from: ogden on April 28, 2018, 10:33:17 amI am in the process of building a 10MHz reference source for my lab. It's based on a pretty stable OCXO and an Extron video amplifier. I believe there are other people on the forum we did use such a device to achieve the same goal.The main point to be aware of is the fact these are generally 75ohm. Whether you want to fix that or not is up to you. Not sure what are the real drawbacks of keeping as is, for a 10MHz signal it should not be such a big deal.In my ref source, I'll also include a rubidium source I purchased years ago (an Efratom LPRO 101) for calibration purpose or when I need really a precise 10MHz signal.DavidEnvoyé de mon GT-N7105 en utilisant Tapatalk

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 11:32:21 am
content: Quote from: douardda on April 28, 2018, 10:54:08 amAttenuation of 50/75 Ohm "mismatch" is very small, around 0.2dB or so. Not worth to even consider "fixing" anything here.

author: douardda
author_rank: Regular Contributor
timestamp: April 28, 2018, 12:22:53 pm
content: Quote from: ogden on April 28, 2018, 11:32:21 amYes that what I had in mind but since I did not do the math I wasn't sure the order of magnitude of this impedance mismatch.Envoyé de mon GT-N7105 en utilisant Tapatalk

author: BravoV
author_rank: Super Contributor
timestamp: April 28, 2018, 02:02:25 pm
content: Quote from: ogden on April 28, 2018, 10:33:17 amThanks, good to know before I made the mistake.Something like this should be fine right ? ->1 Input 8 Output BNC Splitter

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 02:28:46 pm
content: Quote from: BravoV on April 28, 2018, 02:02:25 pmNot good. Bandwidth is just 5.5 MHz. There shall be better choices around. Keep looking

author: BravoV
author_rank: Super Contributor
timestamp: April 28, 2018, 03:54:54 pm
content: Quote from: ogden on April 28, 2018, 02:28:46 pmYeah, what a bummer.Will keep looking, as I'm just hobbyist, I will try to keep at minimal cost as possible.Btw , what the heck is that upper limit 5.5 MHz signal for ? Suitable for analog CCTV signal ?

author: GerryBags
author_rank: Frequent Contributor
timestamp: April 28, 2018, 04:15:17 pm
content: I think you want a distribution amplifier rather than jut a splitter. This one is new (https://www.cctvcamerapros.com/CCTV-Video-Distribution-Amplifier-p/amp-1632.htm), but I've seen lots of 2nd hand units come up on Ebay for around $100 US fairly regularly.

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 05:16:04 pm
content: Quote from: GerryBags on April 28, 2018, 04:15:17 pmLet's check "splitter" I mentioned. First thing we do - carefully read URL:https://www.cctvcamerapros.com/CCTV-Video-Distribution-Amplifier-p/amp-1632.htm.There's specs which say that it's Amplifier indeed:The SB-3701BNC is a 1 in to 4 out Composite BNC Video Distribution Amplifier. Used to distribute video signals to multiple destinations, this product allows up to 4 outputs that are identical to the source signal. Works with any video source with a Composite BNC connector. Video signals can be distributed from up to 300ft (100m). For proper amplification, make sure that your video source is closely located to the amplifier and connected with a short cable.

author: GerryBags
author_rank: Frequent Contributor
timestamp: April 28, 2018, 05:38:37 pm
content: Quote from: ogden on April 28, 2018, 05:16:04 pmYes, I must have missed that. My apologies.

author: DaJMasta
author_rank: Super Contributor
timestamp: April 28, 2018, 06:39:36 pm
content: There's a decent sized recent thread on making your own/buying/converting distribution amplifiers for 10MHz frequency references in the T&M forum, may be worth a search.

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 09:12:19 pm
content: Quote from: GerryBags on April 28, 2018, 05:38:37 pmMy apologies as well. Some clipboard hiccup happened, I managed copy/paste yours, not mine URLAnywayproduct I referto, indeed is distribution amplifier.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: April 28, 2018, 09:46:46 pm
content: Quote from: ogden on April 28, 2018, 11:32:21 amIf you put 25 ohms in front of 50 to get 75 ohms to match then the attenuation would be50/75or in dB20*log(50/(75))=-3.5 dBDid I miss something?

author: ogden
author_rank: Super Contributor
timestamp: April 28, 2018, 10:11:34 pm
content: Quote from: ahbushnell on April 28, 2018, 09:46:46 pmYou do not put anything anywhere. Just connect 50 ohm cable and connector to 75 ohm socket of 75 ohm device, getting 0.2dB loss due to impedance mismatch.https://www.eevblog.com/forum/beginners/using-75-ohm-attenuators-for-50-ohm-applications/http://chemandy.com/calculators/return-loss-and-mismatch-calculator.htm

author: BravoV
author_rank: Super Contributor
timestamp: April 30, 2018, 08:18:11 am
content: Quote from: DaJMasta on April 28, 2018, 06:39:36 pmThanks, just searched and its interesting.Also I found your design, can I get the schematic say in PDF rather have to sign in ?