Cable/Electrical Gurus - I need to measure some cables

[briansmith]

Hi Guys,

I would like to take various cable measurements. I would like to be able to take the following measurements using the meters that I have linked to:

Capacitance - I assume I can use this meter: http://www.************.com/pe/showdetl.cfm?&DID=7&Partnumber=390-735
Inductance – I assume I can use this meter: http://www.************.com/pe/showdetl.cfm?&DID=7&Partnumber=390-513
Resistance – I assume I can use this meter: http://www.************.com/pe/showdetl.cfm?&DID=7&Partnumber=320-076
Nom. Characteristic Impedance: For digital and video cables I would like to be able to measure a cable’s impedance. In other words, how close is it to the 75 ohm ideal? What would I need to measure this?
Dielectric Constant – Is there way to measure this, easily?
Square Wave – Would this meter (http://www.************.com/pe/showdetl.cfm?&DID=7&Partnumber=390-620) allow me to send a sine wave through a cable and see how the cables passes the signal?
Nominal Velocity of Propagation: How is this measured?
Nom. Attenuation (a.k.a signal loss): If I understand this concept correctly this is a measure of the db loss of a given frequency. In other words a 1000ft cable might measure -3db at 20khz. What would I use to measure this? Would I need a 1000ft cable or would you measure a foot and extrapolate from there?

I am complete novice when it comes to measuring and measurements as evidenced by the questions. I full realize some of my terms may be wrong. At this point I am trying to learn what equipment I would need and how to take the aforementioned measurements. I realize equipment can cost thousands of dollars; however, I am looking for the most cost effective solution.

I completely realize that not all of these measurements above can/do affect sound quality. I’d rather not get into a discussion of the same.

Can someone please help me find out what devices I would need and/or point me in the direction of someone that might we willing to take the measurements for a fee? As I mentioned I would be willing to pay someone to help accomplish my goal.

Thanks in advance!

-Brian

 

[briansmith]

In the URLs I listed just replace the stars w/ ************.com

 

[mtrycrafts]

Hi Guys,

I would like to take various cable measurements. I would like to be able to take the following measurements using the meters that I have linked to:


I am complete novice when it comes to measuring and measurements as evidenced by the questions. I full realize some of my terms may be wrong. At this point I am trying to learn what equipment I would need and how to take the aforementioned measurements. I realize equipment can cost thousands of dollars; however, I am looking for the most cost effective solution.

I completely realize that not all of these measurements above can/do affect sound quality. I’d rather not get into a discussion of the same.

Can someone please help me find out what devices I would need and/or point me in the direction of someone that might we willing to take the measurements for a fee? As I mentioned I would be willing to pay someone to help accomplish my goal.

Thanks in advance!

-Brian

Not sure what you are after with all this?
It looks like you want to set up a lab but you have no experience. Not a good start.
Maybe you should call Belden engineering and see how they measure their cables and what instruments they would recommend?

 

[danglerb]

I agree with the last poster, see what Belden et al does, if an accepted methodology exists its best to follow it so your data can be compared to other testing. Once you know how the pros do it, and why, then you can either accept their methods or create something new exploring whatever features you like. What would be bad is to create your own spin, and miss some basic element that makes the data you collect pointless.

 

[mtrycrafts]

I agree with the last poster, see what Belden et al does, if an accepted methodology exists its best to follow it so your data can be compared to other testing. Once you know how the pros do it, and why, then you can either accept their methods or create something new exploring whatever features you like. What would be bad is to create your own spin, and miss some basic element that makes the data you collect pointless.

Yes, all well and good, but maybe he needs some, lot of training first? He has no idea so far. It's not like this is intuitive, unless one has a great knack for this kind of adventure.

 

[briansmith]

Yes, all well and good, but maybe he needs some, lot of training first? He has no idea so far. It's not like this is intuitive, unless one has a great knack for this kind of adventure.

Due to the complexity of the issue I think my best route would be to hire someone who has the equipment and expertise.

So if anyone knows of a contact please let me know!

Thanks.

-Brian

 

[danglerb]

When I want to jump in the water the last thing I want to hear is that I need to learn to swim first. Now I agree learning to float or even swim might be smart, but failing to ever jump in because you failed to make the olympic swimming team isn't so good either. Hours of study wouldn't be as good as what any good engineer could show him with a typical bench in 10 minutes.

Now maybe the meters he tried to link to, I see nothing but stars, are plug in a couple wires and read a value type things, but that doesn't mean the value is anything usefull. Could be, but until we know what he really wants to do, who can say?

 

[danglerb]

Due to the complexity of the issue I think my best route would be to hire someone who has the equipment and expertise.

So if anyone knows of a contact please let me know!

Thanks.

-Brian

Community college, local HAM radio club, most real electronics stores, plenty of PE's for hire too.

 

[mtrycrafts]

Could be, but until we know what he really wants to do, who can say?

Yes, indeed, and he has yet to indicate what he is trying to accomplish by measuring wires that others have not done before.

 

[mtrycrafts]

Due to the complexity of the issue I think my best route would be to hire someone who has the equipment and expertise.
Thanks.-Brian

What are you after with all these measurements? Maybe you can get them from the cable company you buy it from?

 

[briansmith]

Yes, indeed, and he has yet to indicate what he is trying to accomplish by measuring wires that others have not done before.

The reason for needing the measurments is irrevelent. I thought someone might know of a contact.

 

[gene]

Due to the complexity of the issue I think my best route would be to hire someone who has the equipment and expertise.

So if anyone knows of a contact please let me know!

Thanks.

-Brian

I have both but I am not cheap

You may wish to ping Jneutron as he is extremely well versed in these matters and can even connect your cables to his atom smasher

As for measuring squarewaves in a cable, that is complete bunk. See the following post:

http://forums.audioholics.com/forums/showthread.php?t=22028

also reference our cable articles which covers many of the topics you are concerned about:

Audioholics Cable Articles

 

[mtrycrafts]

The reason for needing the measurments is irrevelent. I thought someone might know of a contact.

Oh, but many are very curious why someone without experience was interested in setting up a lab to measure cables?
Hope you have luck with jneutron.

 

[briansmith]

Oh, but many are very curious why someone without experience was interested in setting up a lab to measure cables?
Hope you have luck with jneutron.

Belden referred me to an independant lab. I will be contacting them tomorrow.

Thanks for all the tips.

 

[jneutron]

R,L,C...the links wouldn't work. I assume the meters have the accuracy required for the measures. Read the manual very closely for zero correction.

Line Z: this is simply determined by Z = sqr(L/C). For video, use a test frequency as high as possible.

This method works better than fancy shmancy TDR stuff at home.

Dielectric constant: Not gonna be easy by any means, for non coaxial wires.

For a pure coax, with a braid shield (not spiral) and a non spiral core, use the relation:

L time C = 1034 times DC. L in nH per foot, C in pf per foot.

Edit: Brian, note that this equation is actually a "double braid" equation, where the inner conductor is a hollow conductor to mitigate it's internal inductance...so, does not consider the internal inductance of the center wire. This will be applicable for solid conductors at rather high frequencies, though.

If you measure the inductance of a typical coax, you have to subtract 15 nH per foot from the measurement in order to use the LC product equation.

If the center wire has a relative permeability greater than 1, that 15 nH will be multiplied by that relative permeability. {end of edit}


Prop velocity = 1/sqr(L times C) (fraction of lightspeed is the result..)

Attenuation measurement of a foot of wire will not be accurate enough. Use a long run.

Ummm, why is Briansmith banned?

Cheers, John

 

[gene]

John;

what about your atom smasher?

Ummm, why is Briansmith banned?

Cheers, John

Brian is taking a sabbatical for a week for violating our forum rules in another thread.

 

[jneutron]

John;

what about your atom smasher? .

Which one...the one at work, or the one in my basement??

Actually, I do have one. It's a linear, single source accelerator.. It's not much to look at, but it has a dipole steering magnet and a skew dipole, and it's peak energy capability is 12kev. Beam current's not much, but it suffices to see what I want.

Unfortunately, there are only a few times during the course of a week that it produces output which I consider acceptable..You'd think that with a hundred channels, there'd be more programs to watch. As it is, CSI, 2 1/2 men, HGTV, House, History channel and Jon Stewart are all that I find worthy of steering the beam at the multicolor phosphor target. (boy do I love geekspeek).

Brian is taking a sabbatical for a week for violating our forum rules in another thread.

Ah, ok..

Does a sabbatical mean he does not have the ability to private message?

Cheers, John

 

[danglerb]

If he just needs to measure the length I think my tapemeasure, er lab, can handle that. Metric is going to cost extra though.