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December 2007

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Sun, 2 Dec 2007 15:55:21 -0800
Content-Type:
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text/plain (212 lines)
Classically, you should re-address the issue.

It is common practice to measure the signal and boost the result as close as
possible to the receptor site for low amplitude signals or where the signal
to noise ration will be a distorting factor..

A couple of examples would be a mast head amplifier where the signal is
boosted at point of reception. Another would be a hard drive where the
signal from the spinning disc is amplified at the point of pickup on the
spinning disc.

So maybe I am not understanding this issue, but what is wrong with boosting
the signal or measurement at the probe, by incorporating the electronics
front end within it before it goes into a cable?..............or is this
totally impractical for this application?

John
 
 
John Burke
 
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt
Sent: Sunday, December 02, 2007 2:00 PM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Low Noise Coaxial Cable Question

Joe and Techies

We are carrying out an extensive study on cabling for SIR and should  
have some info that we might be able to publish in due course.

Kindest regards,

Graham

[log in to unmask]



On 30 Nov 2007, at 19:22, Joe Russeau wrote:

> Hello Seth and Inge,
>
> Seth thank you for that very educational response.
>
> Basically, I am researching all of the different SIR test equipment  
> available.  I'm looking into purchasing a newer system (By-the way,  
> this is not an invite to SIR equipment manufacturers to bombard me  
> with product literature). Anyway, one of the groups I have been  
> speaking with recommended using their low noise coaxial cables. I  
> asked how they classified the cable as low-noise. They responded  
> that they pull the cable taught, drop a weight on it and measure  
> the resulting charge.  If no charge, then it is considered low  
> noise.  What I had hoped for with asking my question and the  
> question to TechNet, was to find out what materials were best for  
> low-noise coaxial cables.  I have been contacting different cable  
> manufacturers, who claim to have low-noise cable, to try and  
> determine if the materials sets are consistent from manufacturer to  
> the next. I figured that would allow me to find the cabling and  
> perhaps make the cables myself.  What I have found is that each  
> cable manufacturer uses different materials for their low-noise  
> cable.  So, now I'm back to square one.  So perhaps I should ask  
> the question this way.  If you were in the process of measuring low  
> currents, as is done in an SIR test, and you were looking into  
> coaxial cables as the transfer vehicle from the DUT to the  
> measurement equipment, what materials would you prefer in the  
> cables to give the best data integrity?
>
> Best Regards,
>
> Joe Russeau
>
>
> ----- Original Message ----- From: "Hfjord" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Friday, November 30, 2007 1:27 PM
> Subject: [TN] SV: [TN] SV: [TN] Low Noise Coaxial Cable Question
>
>
> Exellent! However, Joe has still not told us WHAT he wants to do  
> with the
> cable. I doubt he is on a level, that dielectric intrinsic noise  
> will play a
> role. Few test engineers work with such problems. If he isn't a  
> Nobel Prize
> aspirant of some kind. I suggest someone finds remedy against  
> Tinnitus.
> He/she will get the prize, I'm sure. And the inventor will create a  
> lot of
> noise...he-he
> /Inge
>
> -----Ursprungligt meddelande-----
> Från: TechNet [mailto:[log in to unmask]] För Seth Goodman
> Skickat: den 30 november 2007 18:55
> Till: [log in to unmask]
> Ämne: Re: [TN] SV: [TN] Low Noise Coaxial Cable Question
>
> Joe,
>
> Some of what has been mentioned is really part of other cable
> specifications and has nothing to do with noise created in the cable
> itself.  For instance, penetration of electromagnetic fields inside a
> cable shield is often described by the manufacturer's specification  
> for
> shielding effectiveness.  To the extent that the cable has in  
> imperfect
> coaxial shield, it can convert ambient electric or magnetic fields  
> into
> a loop voltage or flowing current.  If external fields are the  
> source of
> your problem, you want cable with high shielding effectiveness as
> opposed to low-noise cable.  For electric fields, improving the shield
> means thicker braid, finer wire in the braid, better conductivity of
> braid wire and plating, more than one braid and/or a foil shield.  For
> magnetic fields, a shielded twisted pair may do better.
>
> The traditional electronic noise sources, which are Johnson (thermal)
> noise, shot noise and a group of unrelated mechanisms that produce 1/f
> noise, do not produce appreciable noise in cables.  When cable
> manufacturers list a cable as low-noise, they usually mean  
> triboelectric
> noise.  If the connected circuit puts a dc potential on the cable,  
> then
> mechanical flexing can change the capacitance between conductors,  
> which
> will cause current to flow in the external circuit.  The triboelectric
> and capacitance change with motion can together be called  
> microphonics,
> as they are both motion-related.  Another source or noise in
> high-voltage cables is leakage.
>
> Regards,
>
> Seth Goodman
>
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