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Co-as cable: truth or nonsense?



 
 
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  #1  
Old November 9th 16, 06:43 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 1,611
Default Co-as cable: truth or nonsense?

Quotes from a recent CCTV trade flier:

Start quotes

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only
61% as effective as copper.

Cheap cable such as CCA (Copper Clad Aluminium) and CCS (Copper Clad
Steel) - Cheaper but in reality a false economy. CCA is around 61%
effective as pure copper and CCS as low as 17% - In layman's terms; If a
copper cable works at 100m then the CCA would only work at 61m and the
CCS at just 17m !!

End quotes

Bear in mind that this is for CCTV, not RF. Since cable TV companies
often use steel cored coax for UHF I find the claims above surprising.

Bill
  #2  
Old November 9th 16, 06:54 PM posted to uk.tech.digital-tv
Phi
external usenet poster
 
Posts: 238
Default Co-as cable: truth or nonsense?


"Bill Wright" wrote in message
...
Quotes from a recent CCTV trade flier:

Start quotes

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only 61%
as effective as copper.

Cheap cable such as CCA (Copper Clad Aluminium) and CCS (Copper Clad
Steel) - Cheaper but in reality a false economy. CCA is around 61%
effective as pure copper and CCS as low as 17% - In layman's terms; If a
copper cable works at 100m then the CCA would only work at 61m and the CCS
at just 17m !!

End quotes

Bear in mind that this is for CCTV, not RF. Since cable TV companies often
use steel cored coax for UHF I find the claims above surprising.

Bill


Silver is the best conductor

  #3  
Old November 9th 16, 07:24 PM posted to uk.tech.digital-tv
R. Mark Clayton[_2_]
external usenet poster
 
Posts: 419
Default Co-as cable: truth or nonsense?

On Wednesday, 9 November 2016 19:54:33 UTC, Phi wrote:
"Bill Wright" wrote in message
...
Quotes from a recent CCTV trade flier:

Start quotes

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only 61%
as effective as copper.


By volume, but by weight it is better - and a quarter of the price - so just make thicker cores.


Cheap cable such as CCA (Copper Clad Aluminium) and CCS (Copper Clad
Steel) - Cheaper but in reality a false economy. CCA is around 61%
effective as pure copper and CCS as low as 17% - In layman's terms; If a
copper cable works at 100m then the CCA would only work at 61m and the CCS
at just 17m !!

End quotes

Bear in mind that this is for CCTV, not RF. Since cable TV companies often
use steel cored coax for UHF I find the claims above surprising.

Bill


Silver is the best conductor


Indeed you can get silver speaker cables! OTOH these are a stupid waste of money.

During WWII there was a shortage of copper, so for the Manhattan Project coils were wound using 13G3g of silver from the US Treasury.
https://en.wikipedia.org/wiki/Manhat...tic_separation
i.e. train loads of the stuff!
  #4  
Old November 9th 16, 08:01 PM posted to uk.tech.digital-tv
Ian Jackson[_5_]
external usenet poster
 
Posts: 42
Default Co-as cable: truth or nonsense?

In message , Bill Wright
writes
Quotes from a recent CCTV trade flier:

Start quotes

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only
61% as effective as copper.

Cheap cable such as CCA (Copper Clad Aluminium) and CCS (Copper Clad
Steel) - Cheaper but in reality a false economy. CCA is around 61%
effective as pure copper and CCS as low as 17% - In layman's terms; If
a copper cable works at 100m then the CCA would only work at 61m and
the CCS at just 17m !!

End quotes

Bear in mind that this is for CCTV, not RF. Since cable TV companies
often use steel cored coax for UHF I find the claims above surprising.

Bill


My understanding is that if the frequency is high enough so that skin
effect forces the current in the inner conductor out into the copper
cladding, it doesn't make much difference what material the core of the
inner is.

With some cables with a copper-clad inner, there's a frequency where the
slope of the attenuation vs frequency curve changes, and there's a
gentle - but noticeable - kink.

In the late 60s, I well remember when we used a length of high loss coax
in the lab to simulate a length of very low loss cable TV trunk cable
(25dB at 220MHz, and solid copper inner in order to carry several amps
of line power current). The requirement was to set up flat, with zero
overall gain, the frequency response of a wideband amplifier (40 to
220MHz).

Out in the field, it was not uncommon to have a cascade of up to (say)
15 amplifiers (and occasionally even more), and with the 'real' trunk
cable, because the amplifiers had been set up flat against the 'kinky'
test cable, there was a very noticeable kink in the frequency response
at around 60MHz - even though this went un-noticed when we initially
compared our lab test cable against a single drum of trunk cable. We
eventually did find a miniature cable (stranded all-copper inner) which
matched the loss characteristics of the trunk cable very closely.
--
Ian
  #5  
Old November 9th 16, 09:53 PM posted to uk.tech.digital-tv
Max Demian
external usenet poster
 
Posts: 3,698
Default Co-as cable: truth or nonsense?

On Wed, 9 Nov 2016 12:24:47 -0800 (PST), "R. Mark Clayton"
wrote:

During WWII there was a shortage of copper, so for the Manhattan

Project coils were wound using 13G3g of silver from the US Treasury.

https://en.wikipedia.org/wiki/Manhat...gnetic_separat
ion
i.e. train loads of the stuff!


I don't know if it's true, but my dad said that during the war we
melted down gold from our reserves for coils (in place of copper) for
military use (which would be well guarded), returning it to the
reserves when it was finished with.

--
Max Demian
  #6  
Old November 10th 16, 12:16 AM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 1,611
Default Co-as cable: truth or nonsense?

On 09/11/2016 20:24, R. Mark Clayton wrote:

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only 61%
as effective as copper.


By volume, but by weight it is better - and a quarter of the price - so just make thicker cores.


The ratio between the diameter of the inner and the outer sets the
characteristic impedance, so the whole cable would be thicker.

Bill
  #7  
Old November 10th 16, 07:47 AM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 6,504
Default Co-as cable: truth or nonsense?

I was always thought the all hf tends to travel on the outside, so plated
cables should be fine.

Often coax that would seem tto be inferior will actually work very well
while some great theoretically superior one won't make any discernable
difference for most uses.
Ido think there is a lot more to consider in such systems than the
conductor material and its plating. Matching and what occurs when you bend
it for example.

Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Bill Wright" wrote in message
...
Quotes from a recent CCTV trade flier:

Start quotes

A solid copper centre core as copper is better conductor of electricity
and signals than gold! So go for copper conductors. Aluminium is only 61%
as effective as copper.

Cheap cable such as CCA (Copper Clad Aluminium) and CCS (Copper Clad
Steel) - Cheaper but in reality a false economy. CCA is around 61%
effective as pure copper and CCS as low as 17% - In layman's terms; If a
copper cable works at 100m then the CCA would only work at 61m and the CCS
at just 17m !!

End quotes

Bear in mind that this is for CCTV, not RF. Since cable TV companies often
use steel cored coax for UHF I find the claims above surprising.

Bill



  #9  
Old November 10th 16, 08:42 AM posted to uk.tech.digital-tv
Jim Lesurf[_2_]
external usenet poster
 
Posts: 4,138
Default Co-as cable: truth or nonsense?

In article , Ian Jackson
wrote:

My understanding is that if the frequency is high enough so that skin
effect forces the current in the inner conductor out into the copper
cladding, it doesn't make much difference what material the core of the
inner is.


In terms of the physics it is probably better to think of this in terms of
the fields mainly being *outside* the conductors, and the fields only
manage to penetrate a limited distance into the conductors.

With some cables with a copper-clad inner, there's a frequency where the
slope of the attenuation vs frequency curve changes, and there's a
gentle - but noticeable - kink.


At low frequencies the field will essentially reach well into the conductor
and use most of the cross-section. As you go to higher frequencies the
cross section becomes limits to the outer 'skin'. Thus, yes, there is a
tendency for a 'knee' to show up in the effective resistance per length.
That then affects both the attenuation and the characteristic impedance.

As per Bill's original point. Gold has a slightly higher conductivity than
copper. So may give lower loss at low frequency. But the higher the
conductance, the thinner the 'skin' at HF. So the cross-section used for
conduction may be smaller. So you may not get the anticipated advantage at
HF.

In the late 60s, I well remember when we used a length of high loss coax
in the lab to simulate a length of very low loss cable TV trunk cable
(25dB at 220MHz, and solid copper inner in order to carry several amps
of line power current). The requirement was to set up flat, with zero
overall gain, the frequency response of a wideband amplifier (40 to
220MHz).


Out in the field, it was not uncommon to have a cascade of up to (say)
15 amplifiers (and occasionally even more), and with the 'real' trunk
cable, because the amplifiers had been set up flat against the 'kinky'
test cable, there was a very noticeable kink in the frequency response
at around 60MHz - even though this went un-noticed when we initially
compared our lab test cable against a single drum of trunk cable. We
eventually did find a miniature cable (stranded all-copper inner) which
matched the loss characteristics of the trunk cable very closely.


Classically, the argument is that the conductor should have many small
conductors. But to work as theory indicates these then should also be
insulated from each other and woven in some way. This then means each
individual stand has a diameter small compared to the skin depth at HF and
shares the current. The 'weave' helps to ensure the strands inside the
bundle are sharing the current. But this means that the insulation gaps
between strands are helping.

In theory, having many thin strands woven so they are in electrical
contact *shouldn't* work as the surface currents can jump from one
'surface' strand to another and avoid having to 'follow the individual
strands' into the bundle. But it probably works to some extent anyway.

Getting cable that truly has the same characteristic impedance and velocity
from DC up to the hundreds of MHz or above isn't easy. You'd tend to also
need to have the dielectic shunt behaviour vary to 'balance' the changes
caused by skin effect, etc. Its no surprise that the widest band cables
then to use small diameters if the don't need to carry much power.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

  #10  
Old November 10th 16, 10:10 AM posted to uk.tech.digital-tv
Ashley Booth[_2_]
external usenet poster
 
Posts: 90
Default Co-as cable: truth or nonsense?

Jim Lesurf wrote:

In article , Ian Jackson
wrote:

My understanding is that if the frequency is high enough so that
skin effect forces the current in the inner conductor out into the
copper cladding, it doesn't make much difference what material the
core of the inner is.


In terms of the physics it is probably better to think of this in
terms of the fields mainly being outside the conductors, and the
fields only manage to penetrate a limited distance into the
conductors.

With some cables with a copper-clad inner, there's a frequency
where the slope of the attenuation vs frequency curve changes, and
there's a gentle - but noticeable - kink.


At low frequencies the field will essentially reach well into the
conductor and use most of the cross-section. As you go to higher
frequencies the cross section becomes limits to the outer 'skin'.
Thus, yes, there is a tendency for a 'knee' to show up in the
effective resistance per length. That then affects both the
attenuation and the characteristic impedance.

As per Bill's original point. Gold has a slightly higher conductivity
than copper. So may give lower loss at low frequency. But the higher
the conductance, the thinner the 'skin' at HF. So the cross-section
used for conduction may be smaller. So you may not get the
anticipated advantage at HF.

In the late 60s, I well remember when we used a length of high loss
coax in the lab to simulate a length of very low loss cable TV
trunk cable (25dB at 220MHz, and solid copper inner in order to
carry several amps of line power current). The requirement was to
set up flat, with zero overall gain, the frequency response of a
wideband amplifier (40 to 220MHz).


Out in the field, it was not uncommon to have a cascade of up to
(say) 15 amplifiers (and occasionally even more), and with the
'real' trunk cable, because the amplifiers had been set up flat
against the 'kinky' test cable, there was a very noticeable kink in
the frequency response at around 60MHz - even though this went
un-noticed when we initially compared our lab test cable against a
single drum of trunk cable. We eventually did find a miniature
cable (stranded all-copper inner) which matched the loss
characteristics of the trunk cable very closely.


Classically, the argument is that the conductor should have many small
conductors. But to work as theory indicates these then should also be
insulated from each other and woven in some way. This then means each
individual stand has a diameter small compared to the skin depth at
HF and shares the current. The 'weave' helps to ensure the strands
inside the bundle are sharing the current. But this means that the
insulation gaps between strands are helping.

In theory, having many thin strands woven so they are in electrical
contact shouldn't work as the surface currents can jump from one
'surface' strand to another and avoid having to 'follow the individual
strands' into the bundle. But it probably works to some extent anyway.

Getting cable that truly has the same characteristic impedance and
velocity from DC up to the hundreds of MHz or above isn't easy. You'd
tend to also need to have the dielectic shunt behaviour vary to
'balance' the changes caused by skin effect, etc. Its no surprise
that the widest band cables then to use small diameters if the don't
need to carry much power.

Jim


Hence Litz wire https://en.wikipedia.org/wiki/Litz_wire

Ashley

--

 




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