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Test Leads for Oscilloscopes, Function Generators etc

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Musicmanager

Well-Known Member
Hi Guys

Yet another question !
I've got my 'scope up and running, the probes have arrived today and I've ordered the bits to make my Function Generator and Frequency Counter. I want to obtain some fly leads to connect together and to test work, ie. BNC to BNC; BNC to crocodile; maybe others ?
I've been reading about 'noise' and high impedance on some cables and the problems caused. There seem to be a lot of cables available but mostly of asian origin which unnerves me slightly. Is there a recommended standard/source to go with ? Would I be better off buying cable and fittings and making up myself ?
I'd appreciate your advice
Thanks
S
 
There are commercial sources for such connections such as Pomona Electronics. They are not cheap but they are good quality.
A supplier such as Farnell should sell good quality cables.

Generally cable quality is more related to reliability and long life as compared to noise or impedance problems. Usually if there are those problems it comes from some sort of mechanical failure in the cable assembly.

I would buy completed cables rather than making them. Completed cables usually have molded connectors which are less prone to opens and shorts due to cable flexing.
 
I like to make my own.

You can pick up decent quality BNC cables for example from places like CPC for a reasonable price and adapt them to your needs.

Heatshrink sleeving is useful for a quality finish.
 
I also like to make my own cables.
In the UK, I recommend these guys for coax cable and connectors:
http://www.whwestlake.co.uk/

If you buy some cable and BNC connectors, it is a good practical exercise fitting the connectors correctly.

When buying BNC connectors, be aware that there are two "types" 50 Ohm and 75 Ohm.
For most general purposes you want 50 Ohm, these days 75 Ohm is (usually) only used for video applications.
Having said that, in BNC type connectors, 50 and 75 Ohm types will fit together and most people will not know the difference until you get to high frequencies ( High in this case is several MHz).
The same is not true for "N type" connectors, the centre pin is a different diameter, putting a 50Ohm plug into a 75Ohm socket will wreck the socket. Been there, done that, but only once!

JimB
 
Hi Jim

Thanks for that. Quick look down their stock list has some surprises in terms of good prices. They have several other bits I've been looking for and couldn't find. I'll get an order in to them soon.
In 1998 I moved to a new teaching job in Banbury at a school that had a Music Technology suite. I managed to break 16 computers by putting the wrong BNC plug into sockets on the processors which connected the peer to peer network. I only did that once too !!
In terms of what I need - BNC to BNC approx 500 mm and 1 metre; BNC to crocodile pair similar lengths; crocodile to crocodile similar lengths.

Anything else ??

S
 
Anything else ??
How much of your money would you like me to spend?

Here is my rack of test leads, BNC to BNC, N to BNC, PL259 to BNC, BNC to Crocs, IEC Mains Leads and a few real oddballs.
Test Lead Rack.jpg

A box of assorted inter-series adaptors an connectors and oddballs.
Assorted connectors and adaptors.jpg

A couple of BNC Tee Pieces is useful for when you want to connect two bits of equipment to the same point.
BNC Tee Piece.jpg

Not all signals arrive on a BNC terminated coax cable, so some BNC to 4mm plugs and sockets is useful.
BNC to single 4mm Terminal.jpg BNC to 4mm Plugs.jpg BNC to two 4mm Terminals.jpg

And last but not least, ALWAYS usefull, some Croc Leads made with single wire rather than coax/screened cable.
Croc Leads.jpg
Use them for power (low volts DC), signal connections where screening is not important, little friggs and jumpers where a temporary connection is required to make something work.

Of course, all this lot did not just appear at once, it has built up over 50 odd years of playing with radio and electronics.

JimB
 
Morning Jim

Thank you, that's very useful.
Some of the bits I've already got like the single wire crocs and BNC tees and since I started using a small ready built power supply from china I've also got
several twin wire ( red & black ) crocs. N & PL259 need some research, I don't know what they are yet. My usual style is to make an Excel list from your suggestions and gradually build the stock in line with cash flow.
My target is related to that reading you sent me. I've been reading and reading but only able to 'imagine' hypothetical set ups, there is a limited understanding. I want to use the equipment and set up some practice opportunities so that the understanding goes in and stays !

Bit of a hiccups with the 'scope leads that cam yesterday, the x1/x10 switch on one probe is stuck rigid and is likely to break off soon so I've sent them back for a replacement set, fortunately, supplier is local not China !

Finally, I've concluded that you must be bionic ! You left the most recent post at 1.50am which doesn't seem unusual for you, but you are often here 1st thing also ! When do you sleep ??? LOL

Thanks again

S
 
N & PL259 need some research, I don't know what they are yet.

Both are pretty rare, not something you're likely to need to concern yourself with :D

PL259 were used for CB and Amateur radio's, and for a few VERY, VERY old VCR's - apart from that it's mainly professional use.

I don't have a single PL259 lead or plug in the service department I run, and I've NEVER had an N type plug or lead (although I do know what they are).
 
N & PL259 need some research, I don't know what they are yet
Unless you are into radio, you do not need those connectors, I was just describing what is in my box of bits.

Here on the front of my frequency counter are two inputs,
Input A for 5Hz to 160MHz and Input B for 80MHz to 2.6GHz.
BNC and N.jpg

For ease of day to day use, I normally have an N to BNC adapter on the B input.


JimB
 
Morning Jim

Well, my 'scope is not that posh ! I only have 3 BNC connections, Ch 1; Ch 2; and External Trigger !

S
 
Jim

I've just had an email back from WHWestlake saying their connectors are not good enough quality for test leads and I should buy Pro sets !!

S
 
Musicmanager May I ask what you will be using the scope for???

I have several scopes... I have cheap probes.. I have expensive probes.... I have home made probes...

The reason I bring it up is... I don't really do analogue stuff.. A bit ( interfacing and stuff ) but on the whole.. Not a lot... I use my digital scope daily... My storage scope very rarely.... But as I do digital electronics, even crappy leads show me what I want to know.. I agree that crappy probes introduce a noise level, but at 3v and 5v around 20Mhz , its irrelevant...

If you are measuring signals in the order of millivolts at frequencies above Khz then better probes are advised...
 
Hi Ian

The short answer is I don't really know ! I'm a complete novice but I've learnt a lot from people on here.
I've bought an old Gould OS4000 'scope, cleaned it and got everything tickety-boo. My main purpose at the moment it to learn when and how to use it and to that end JimB gave me some reading matter which is great but in total too much to take in hypothetically, so.. I've got bits on the way to make a Function Generator and a Frequency Counter so I can hook up and play and get to know by practice what the book is trying to teach me.

Probes are not an issue, I have some and better ones on the way here. What I need are the hook up cables BNC to BNC; BNC to croc . I'm not likely to get into radio so PL259 or N are not on the list.
My real question - if you look to buy made up they go from ridiculously cheap to ridiculously expensive and everyone seems to favour making up your own - so I'm now looking for good quality bits and cable to do my own.

Regards

S
 
I've just had an email back from WHWestlake saying their connectors are not good enough quality for test leads and I should buy Pro sets !!

I feel very confused, what exactly was the question you asked them?

JimB
 
In train of contributing to happily spending your money, may I suggest these grabbers, good to reach difficult points? Pity is I bought just very few of them when still available locally

grabbers.jpg
 
I cannot help but think that Mr Westlake is:
a/ Over estimating your requirements.
b/ Doing his products a dis-service.
c/ Both of the above.

So with that in mind, I have had a look at his website and on the Price Lists pages I suggest that the following will do exactly what you want:


Cable and wire products

RG58CU…5mm dia high quality cable to Mil spec..with stranded centre conductor.
Very Flexible….PRICE 50p per metre. (100m drum price is £45)

Connectors and Components - Page 2:
Mil Spec. BNC to take 5mm coax..with PS gland………………………..…..£2..50
BNC Coupler..2 sockets back to back in line…………………………………….£1..60
BNC ADAPTOR…2 x sockets and 1 x plug outlets…………………………..£3..00 (Tee Piece)

Connectors and Components - Page 6:
Small Mini Croc clips..with red or black covers………………………………..15p

JimB
 
Thanks Jim

I'll send him an order based on that. I've deleted the attachment - I don't think it's fair to leave for all to see.

S
 
Jim

One question BNC with PS gland - pressure sleeve gland ? Need crimping or screw in ??

S
 
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