Selecting the right BNC cable? - Page 1
Forum section: electronics / beginners

author: nbritton
author_rank: Frequent Contributor
timestamp: October 27, 2015, 10:12:45 pm
content: I'm a total newbie when it comes to BNC cables. Most of the cables I see have no specifications. I need a cable that is capable of 500 MHz bandwidth at a minimum and ideally 1 GHz for extra margin of error. Can I use any BNC cable or do I need something special?

author: Paul Price
author_rank: Super Contributor
timestamp: October 27, 2015, 10:17:55 pm
content: It is not just the cable but the impedance of the cable to match your signal source/load. Good quality 50-ohm/75-ohm cables will usually do well up to approx 2GHz depending on the amount of loss/meter and VSWR you can tolerate.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 27, 2015, 10:51:16 pm
content: Quote from: Paul Price on October 27, 2015, 10:17:55 pmSorry, it would be 50 ohm... to hookup a 50 ohm signal generator (1.5 MHz square wave with 500ps rise time) into a 50 ohm terminated 500 MHz oscilloscope. So in other words what you are saying is any 50 ohm BNC cable off the shelf will work at 500 MHz bandwidth?

author: TimFox
author_rank: Super Contributor
timestamp: October 27, 2015, 10:57:06 pm
content: Full mil-spec 50 ohm BNC connectors themselves are good to past 2 GHz. Seehttp://media.digikey.com/pdf/Data%20Sheets/Bomar%20PDFs/BNC_Products_Spec.pdfThere are other connectors that are compatible with BNC connectors, but do not meet the full mil-spec at high frequency. Seehttp://www.amphenolrf.com/031-2-rfx.htmlAt 0.5 to 1.0 GHz, the loss of the cable assembly is probably dominated by the cable, specified in dB per length.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 27, 2015, 11:37:00 pm
content: What type of coax should I pick? RG-8X?Edit: what do you think of this cable?:www.amazon.com/MPD-Digital-rg8x-bnc-antenna-cable-2FT-MILSPEC-Connectors/dp/B00TCQHE8O

author: tautech
author_rank: Super Contributor
timestamp: October 28, 2015, 12:19:40 am
content: Quote from: nbritton on October 27, 2015, 10:12:45 pm1 GHz really? Just for GP use or "something special"?Quote from: nbritton on October 27, 2015, 11:37:00 pmFor just GP work RG-58 C/U 50 Ohm is fine and 1M lengths with BNC's can be found on Aliexpress for ~$10 ea.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 28, 2015, 12:22:32 am
content: http://www.rfconnector.com/rf-cable-guide.phpPut it in a spreadsheet and sort on the tradeoffs in frequency, attenuation, conductor type, diameter, etc.Some to consider include LMR200, RG223, RG400, RG58, RG174, RG316. Depends on whether you are optimizing for price or something else. You can make your own or plenty to choose from on Amazon and eBay, along with the rest of the Internet. Cable diameter and flexibility might considerations to keep I mind along with attentuation, and shorter is better if you are trying to squeeze out performance - but too short won't be very useful.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 28, 2015, 02:31:10 am
content: Quote from: tautech on October 28, 2015, 12:19:40 amThe bandwidth on the scope that I just bought is 500 MHz, but I hear it can see well passed 1 GHz, so I would like to get a good cable that meets all use cases.Quote from: tautech on October 28, 2015, 12:19:40 amI found an attenuation chart here:http://www.w4rp.com/ref/coax.htmlA 3 foot RG-58 cable would be 0.645 dB loss @ 1 GHz, whereas a 3 foot RG-8X cable would be 0.405 dB loss @ 1 GHz. Not much difference, but enough for me to spend the extra $3 for a cable that is made in America and meets MIL spec and has 2-day amazon prime shipping.

author: nbritton
author_rank: Frequent Contributor
timestamp: October 28, 2015, 02:46:08 am
content: Quote from: Electro Fan on October 28, 2015, 12:22:32 amI would like a cable that is flexible, I believe LMR and RG223 uses a solid conductor so those would be out.

author: sequoia
author_rank: Unknown
timestamp: October 28, 2015, 03:55:06 am
content: Amazon has some pretty nice B&K Precision cables that are not that expensive including BNC to BNC (that are listed up to 2GHz):http://www.amazon.com/Precision-CC251-Insulated-Coaxial-Cable/dp/B00TTOWEIO/(for $17.50)Some Amphenol cables can be found as well for about half the price:http://www.amazon.com/Amphenol-CO-058BNCX200-006-Black-Coaxial-Cable/dp/B00O070D4W/

author: nbritton
author_rank: Frequent Contributor
timestamp: October 28, 2015, 04:38:11 am
content: Quote from: sequoia on October 28, 2015, 03:55:06 amI don't think those Amphenol cables are legit. Here is one of the reviews for them:Quote

author: dadler
author_rank: Unknown
timestamp: October 28, 2015, 04:41:27 am
content: I like the Probemaster BNC cables:http://probemaster.com/bnc-cables/

author: LukeW
author_rank: Frequent Contributor
timestamp: October 28, 2015, 10:00:21 am
content: Every time I need a RG58 instrument patch lead and can't find one I always think of the millions of 10BASE2 cables that schools and offices must have thrown in the trash.

author: han
author_rank: Frequent Contributor
timestamp: October 28, 2015, 11:07:07 am
content: Selecting cable you have to determine these factor:1. Total attenuation accepted (to determine max length)2. Length(for determine cable type at accepted attenuation)3. Max VSWR (for full span frequency you need)4. Max powerbut for typical use <1G i use cheap BNC with RG58 cable (1m or less) will be sulficient