Oscilloscope probe to BNC - Page 1
Forum section: electronics / beginners

author: 555Rich666
author_rank: Newbie
timestamp: June 06, 2016, 02:51:13 am
content: After watching the video about using a BNC cable from a function generator to an oscilloscope he showed an adapter that went onto the end of his oscilloscope probe. I tried to buy that adapter on Amazon and they have 2 different kinds. How do I know if I should buy the 3.5mm one or the 5mm one?

author: tautech
author_rank: Super Contributor
timestamp: June 06, 2016, 03:28:56 am
content: Welcome to the forum.The size you need is entirely dependent on the probe you have, measure the diameter of the reference (GND) ring above the probe tip with the grabber hook removed.If you have a range of probes you may want both sizes.

author: 555Rich666
author_rank: Newbie
timestamp: June 06, 2016, 08:32:46 pm
content: Thanks so much. I was thinking that was it since the only thing that measured 3.5 or 5.0 mm was the 5.0 mm of the ground ring. I just bought an oscilloscope and a signal generator and am trying to get all the probes that I may need. It's too bad that I have to buy a bag of 10 when I probably only need 2. Amazon also sells a bag of 10 probe cover shells for $20, do I need this? I already bought BNC to alligator clips, cables. And, BNC to grabber clips, cables. I'm just getting back into tinkering/learning electronics now that I'm retired. Can you suggest anything else I should get?

author: tautech
author_rank: Super Contributor
timestamp: June 06, 2016, 08:56:13 pm
content: Quote from: 555Rich666 on June 06, 2016, 08:32:46 pmOften the adapters come supplied with the better quality and higher BW probes....there have been a few requests for sources of them here and failing finding those threads with a search (use the Search button, not the box) there may be another member with a suppliers link for you.Quick look on eBay found this one:http://www.ebay.com/itm/Probe-Tip-Adapter-allows-connecting-probe-to-scope-port-DiLette-DL-PA009-BNC-/252406586228?hash=item3ac49adb74:g:KwsAAOSwepZXSz3pThere will be others, a little time searching will find them.If you intend to do any HV work, say over 300V a 100:1 probe is a good idea and these normally come with the BNC adapter....but check first. But they don't fit all probes as you are now aware.You can also find lots of goodies herehttp://www.aliexpress.com/but searches can be frustrating, the keywords you use are critical for success.A couple of BNC to BNC cables are a must....cheap ones with dubious performance for other than a few MHz can be got for just a few bucks but if you want to go into the GHz you need quality cables.

author: 555Rich666
author_rank: Newbie
timestamp: June 07, 2016, 02:52:49 am
content: Thanks, I'll look at those web sites for some bargins. Do I need the probe cover shells for the adapters? I'm not sure if their purpose is to protect the scope from shorting out when you connect the adapter or something else.

author: tautech
author_rank: Super Contributor
timestamp: June 07, 2016, 05:41:02 am
content: Quote from: 555Rich666 on June 07, 2016, 02:52:49 amNa, you need the Gnd ring on the probe to conduct with the BNC adapter.Think of it this way:Any waveform that you wish to observe must have a reference...with most scopes this is mains Gnd and for waveforms to be correctly propagated along cables the shield (Gnd) need be continuous.However you need to be cautious where you reference a waveform to as is explained in Daves often linked vid:

author: natman69
author_rank: Regular Contributor
timestamp: June 07, 2016, 02:04:37 pm
content: I was looking at the same adaptors but I haven't ordered them because I really need 2-3 pieces of each model (3.5 and 5 mm) but they're available from Amazon or Caltest only in a minimum quantity of 10 for each diameter.Maybe we can do a single order and then divide the connectors?

author: 555Rich666
author_rank: Newbie
timestamp: June 07, 2016, 02:26:09 pm
content: To Tautech, Thanks for the help. To Nautman69 I don't think I'll need the 3.5mm ones since I don't have any of those probes but I'm planning on buying the 10 pack of the 5.0mm ones so I'll have extras if you want me to send you 3 I will.

author: sanman
author_rank: Contributor
timestamp: June 07, 2016, 02:33:38 pm
content: Depending on your scope and the output of your signal generator you might also consider a 50-ohm terminator.

author: MarkF
author_rank: Super Contributor
timestamp: June 07, 2016, 04:59:47 pm
content: Quote from: sanman on June 07, 2016, 02:33:38 pm+1 on the 50 ohm feed through terminator.Really, how often are you going to probe a BNC connector? I would think a 50 ohm coax cable, BNC T's and a 50 ohm terminator would get more use with your signal gen.Cal Test Electronics CT2944 Feed-Thru Coaxial TerminatorElenco BNC to BNC Cable

author: sanman
author_rank: Contributor
timestamp: June 08, 2016, 01:16:03 am
content: Mark F. That is the terminator that I purchased. Works well at a decent price!

author: 555Rich666
author_rank: Newbie
timestamp: June 08, 2016, 01:20:43 am
content: To sanman and MarkF, I was planning on buying a T and a 50 ohm terminator anyway but I didn't know that would work. If I understand this right I should connect the T to the Scope and then connect the BNC cable coming from the Generator to one end of the T and the 50 ohm terminator to the other end of the T. Is this right? If so I think you solved my problem without spending another $35. Thanks to you both.

author: 555Rich666
author_rank: Newbie
timestamp: June 08, 2016, 01:28:13 am
content: To MarkF,After looking at that terminator you suggested, I guess I wouldn't need the T. Is that true? Although I'll probably buy a couple anyway just to have.

author: MarkF
author_rank: Super Contributor
timestamp: June 08, 2016, 02:43:40 am
content: Quote from: 555Rich666 on June 08, 2016, 01:28:13 amOnly if you intend to feed something else beside just measuring the signal on the scope.Also, you would want the 50 ohm termination at the end of the daisy chain.

author: MarkF
author_rank: Super Contributor
timestamp: June 08, 2016, 02:46:49 am
content: Quote from: sanman on June 08, 2016, 01:16:03 amI only bought one. Wishing I had a 2nd one just to have available.

author: MarkF
author_rank: Super Contributor
timestamp: June 08, 2016, 03:16:33 am
content: Here are two videos you may find helpful:

author: tautech
author_rank: Super Contributor
timestamp: June 08, 2016, 04:14:39 am
content: Had a mo to do a forum search for adapters for the OP, some links:https://www.eevblog.com/forum/testgear/scope-probes-as-supplied-by-rigol-for-the-low-end-scopes-a-discussion/https://www.eevblog.com/forum/testgear/rigol-scope-probe-to-bnc-adapter/https://www.eevblog.com/forum/beginners/oscilloscope-probe-adapter/