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Old 21st June 2011, 08:45 PM   #1
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Default BNC Cable Questions

Hi everyone!

I recently purchased:

-Tek 465 100Mhz Oscilloscope ($100)
-Wavetek 142 HF VCG Generator ($80)
-B&K Precision 1820 80MHz Universal Frequency Counter ($11)

The function generator and frequency counter didn't come with any probes, so I've been wondering which cables you would recommend that I get.

What would be the best BNC type cables for them?

Also, has anyone ever used a VCG Input for a signal generator?


Thanks a lot!
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Old 21st June 2011, 09:01 PM   #2
AuroraB is offline AuroraB  Norway
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Generators and counters don't come with probes....
As long as you're not operating at GHz level, which you're stuff don't support anyway, any decent 10$ BNC cable will do - 50 ohms RG58 preferrably, but impedance doesn't matter if you're not operating with terminated impedance RF circuits. Audio is very rarely defined for 50 ohms termination, anyway.
Get a few cables from anywhere ( Ebay?), make sure you get some 6-8 ft ones you can cut in half, for phono plugs, croc clips or similar.
Beware that if you're generator is defined with 50 ohm output, you're dial readings will probaly not be correct into higher impedance loads, ( -kohms and higher ) - output level will usually be higher - up to 2x the reading....
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Old 21st June 2011, 09:20 PM   #3
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Good prices. ! I wonder if the wavetek has a DC blocking cap inside. My concern is that if you are injecting audio into an amp and get the center conductor of the wavetek on some DC voltage you could damage it. Its real nice to get manuals for your test equipment, and you might find them for free.
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Old 23rd June 2011, 01:06 PM   #4
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the Wavetek 142 will be DC Coupled to enable the variable DC Offset on it's output.

A manual for it is available here if you don't have one:
Download Manuals for Free -- Wavetek 142 Generator
The VGC input is explained in the Manual.

Suggest that you get one of the BNC in-line boxes like this one:
RS | Connectors | RF / Coaxial Connectors | Connector RF | In-Line Component Cases & Coaxial Line Surge Protectors
and fit a 10F 63V poly cap inside it to block DC.

A couple of BNC 'Tee' Adapters will also be useful to you.

hope this assists
Mik
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Old 23rd June 2011, 08:04 PM   #5
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If you are states side, I use www.jameco.com Nice selection of reasonable quality cables.

paul
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Old 24th June 2011, 12:57 AM   #6
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Quote:
Originally Posted by AuroraB View Post
As long as you're not operating at GHz level, which you're stuff don't support anyway, any decent 10$ BNC cable will do -
I tend to agree with that, for light-duty, casual use. The difference between inexpensive and expensive test cables tends to show up after they have been in service for a while - been yanked a few times - got pinched in a drawer once or twice - stepped on or rolled over by a desk chair - the connector pins start to shed plating - and they get noisy or intermittent. Then you either clip off the offending connector, or tie a good overhand knot in it and toss it into a box. On some rainy Friday afternoon when there isn't much happening around the lab, you start going through them and replacing connectors or scrapping the cable entirely.

No matter how many test cables you have, you will always need one more. The ones you have are either 6 inches too short, or don't have exactly the combination of connectors you need.

( In many cases I have assembled my own test cables on an as-needed basis. Yeah, it's a somewhat time consuming irritation. In a prior incarnation I developed a great respect for the performance, ruggedness, and longevity of the "Wrench-Crimp" RF connectors (BNC et al) from Trompeter Electronics - but that was before they were bought by Emerson. They were never inexpensive, or easy to find. I still have a few that I salvaged from old cable assemblies, that I use for repairs and such. Other manufacturers probably have similar BNC connectors that are worth keeping on-hand for use as the need arises.)

Dale
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Old 24th June 2011, 08:33 PM   #7
AuroraB is offline AuroraB  Norway
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Coaxial cables and connectors are designed for RF use, and quality RF components are expensive! Workwise, I pay from 5$ to 50$ for N-BNC adaptors, - the latter from Huber-Suhner are rated for 20GHz, while the cheap ones from Radiall are unknown......
Also , in pro environments, Coax adapters seemingly have an extremely high "evaporation rate".......

- Agreed- you'll always need one or two more than you have....
junk yards or surplus shops may be an asset to hobbyists.. and as quality coax connectors and adapters are silver plated, silver dip cleaner actually works quite well!. Just make sure to rinse and dry properly afterwords.....
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Old 24th June 2011, 09:39 PM   #8
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Is it usefull to go for a function generator that comes with a sweep function?
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Old 24th June 2011, 09:58 PM   #9
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Hey everyone, thanks for the responses! I ended up buying two six foot 50Ω BNC cables, as well as some BNC T-adapters for starters. Also, thanks for the tip on the in-line box; that's the next thing that I'll purchase!


digits, here are some statements made by SY in this thread:

Quote:
Sweep is a nice convenience, but normally not necessary. Understand that a function generator will have relatively high distortion, so they're useful for certain types of amp testing (e.g., power out, gain, stability, frequency response) and less so for others (THD).

For distortion testing, you can either build a notch filter (restricts you to a single frequency), use a software/soundcard source, or buy a separate sine-wave-only generator. Or do what I did and find a kind soul who will loan you a distortion analyzer. The software solution has the disadvantage of limited frequency span, but the advantage of features like sweep and tone-burst.

With the basic tools you've got now, you're ready to go into battle!

Sweep can be a nice backup method to FFT or MLS testing for frequency response when paired with some sort of X-Y recording device. Or it can be a primary method if you don't like using computers, but that's taking the retro concept too far for my tastes.

I'm so amped to get started! I picked up a Weller WES51 yesterday too.
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Old 27th June 2011, 06:09 AM   #10
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My scope has an FFT function in the software apparently, I had to settle for a rather crappy function generator due to shipping costs, and the prices the nice ones reach on auction.. it was like the only one with a buy it now option, to lock in my losses.
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