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November 2007

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Subject:
From:
Joe Russeau <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Joe Russeau <[log in to unmask]>
Date:
Fri, 30 Nov 2007 14:22:06 -0500
Content-Type:
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text/plain (118 lines)
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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