BNC to female header adaptor for scope - Page 1
Forum section: electronics / general

author: HAL
author_rank: Newbie
timestamp: June 15, 2011, 04:57:10 am
content: Hi guys! New guy here.Dave mentioned in one of his videos about an excellent connector for probing male headers. It was a BNC to female header adapter, with BNC on one end and two wires on the other end with two single female headers attached. Using a regular scope probe is way less convenient and is prone to shorting out to adjacent pins.I am hoping this recommended adapter is compatible with .1 inch spaced headers, and i haven't found a similar part anywhere, so i'm wondering if anyone can provide a part number? Thanks for your help.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 15, 2011, 07:18:06 am
content: Quote from: HAL on June 15, 2011, 04:57:10 amwhich video?

author: HAL
author_rank: Newbie
timestamp: June 15, 2011, 07:34:18 am
content: I can't find it again, but i think it was somewhere in the equipping your electronics lab video. I went through it several times but never found it again...

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 15, 2011, 08:00:45 am
content: it depends on what you want to do with it. for high frequency measurement, try to avoid loose wires as i got an advice from 5 stars member here in my threadHow to Better Wire the BNC Connector and GHz issue. at ~>30MHz, you start to see some weird stuffs even at loosely made coax and bnc, worst for unshielded cabling. i doubt Dave will recommend such a probe, maybe only for bench dmm stuff like that. but not for scope. as the late Jim Williams said, the best cable of all is "no cable". may he rest in peace.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 15, 2011, 10:33:16 am
content: For low impedance, low frequency signals you can do whatever you want. What you describe will work just as well as a BNC to alligator or BNC to those hook test clip leads.If you can tolerate a 50 ohm load you can do the same thing without wiring. Just solder the header onto the cut-flat end of a coax cable and put heat shrink tubing around it. Then set your scope to 50 ohm mode or use an external terminator.If you need to avoid loading your circuit too much you can make a transmission line probe. Solder a 450 ohm or 4950 ohm chip resistor in series with the center conductor and the header. Again, terminate your scope to 50 ohm. You get a x10 or x100 probe with easily 1 GHz of bandwidth if you are careful.You can make a standard 10 megaohm passive probe the same way, but you need a compensation network. Rather than go to the trouble, I would just make a small adapter that you can insert the probe tip into and clip the ground lead to -- leave it to your scope manufacturer to make a proper passive probe.

author: Floyo
author_rank: Regular Contributor
timestamp: June 15, 2011, 11:00:36 am
content: do you mean these leads?http://uk.farnell.com/hirschmann-test-measurement/bnc-al-0-64/test-lead-bnc-0-64mm-socket-1-2m/dp/4017468?Ntt=bnc+0.64+mm

author: HAL
author_rank: Newbie
timestamp: June 15, 2011, 10:56:36 pm
content: Quote from: Floyo on June 15, 2011, 11:00:36 amThat's them! Thanks Floyo.

author: Unknown
author_rank: Unknown
timestamp: June 15, 2011, 11:30:21 pm
content: This is not a scope probe anymore than a coat hanger is a scope probe. It will present a huge capacitive load which will destroy any high-frequency response if not properly terminated, and a fairly low resistive load if properly terminated (with poor impedance matching because of the variable spacing between the leads). But it may be OK for audio frequencies or similar. A scope probe is not just a piece of coax with a funny looking tip.There are some scope probes/accessories designed for 0.1" headers (example), but only the $$$ brand-name ones. The cheap brands like Rigol only appear to imitate the probes Tektronix made about thirty years ago for some reason, even though component sizes have decreased dramatically.

author: HAL
author_rank: Newbie
timestamp: June 15, 2011, 11:34:35 pm
content: Quote from: alm on June 15, 2011, 11:30:21 pmGreat! Thanks Alm. I'll take a look at the Tektronix accessories.

author: Mechatrommer
author_rank: Super Contributor
timestamp: June 16, 2011, 02:19:25 am
content: if you think the brand name is expensive. you can diy something like thishttp://koti.mbnet.fi/jahonen/Electronics/DIY%201k%20probe/.from my observation, the trick is try to minimize the "split wire" as much as you can, so the loss is minimal, probably usable up to few hundreds MHz.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 16, 2011, 06:49:32 am
content: Of course,you aren't always critically looking at high frequency signals.In many cases,you are checking DC supply pins on the header,or low frequency signals.One thing that works OK with the inline header/sockets which are commonly used,is the needle part of a hypodermicsyringe.These are usually thin enough to slide into the back of a socket alongside the connector pins.A normal probe is then clipped onto the needle.Needless to say;Not used ones!!A long pin would do as well.Obviously,there are frequency limitations,but it is a useful trick,as the centre of most probes is too fat to fit in the back of a socket in this manner.VK6ZGO

author: Unknown
author_rank: Unknown
timestamp: June 16, 2011, 11:51:55 pm
content: Quote from: Mechatrommer on June 16, 2011, 02:19:25 amWith proper construction, bandwidth in the order of the 100MHz shouldn't be a problem. There are even someinstructions for a slightly more complex resistive probe that claims to go to 1GHz. You do have to terminate it into 50 ohms, however, and if you want to come anywhere near 1GHz, you need a scope with 50ohm input (1Mohm inputs seldom go beyond 500MHz anyway). You also need to be able to tolerate the low DC impedance of a few hundred ohms to a few kohms. Impedance at high frequencies is actually better than a 'Hi-Z' probe, because of the much lower capacitance. Howard Johnson is a big fan of resistive probes, but remember that he's dealing with fast digital circuits, which need a low output impedance anyway to meet their fast edge rates.

author: Rufus
author_rank: Super Contributor
timestamp: June 18, 2011, 03:24:10 pm
content: Unless you want a 50 ohm termination you would be better off wiring a couple of short flying leads with pin sockets to a BNC socket and using the BNC adapter than comes with most scope probes.