[OT] Drain Wire on CAT6 RFI resistant cable?

[Brian - N5BCN]

Thanks to Don and Jim for their input on building a RFI resistant control cable.

I've been informed by another poster that it's recommended to use stranded CAT5 or 6 verses solid wire.  The poster believes stranded wire would be more resistant to flexing, plugging, unplugging, etc. than solid wire.

One last question on this issue:

I've come across some nice (stranded) CAT6 cable that has a shield and a drain wire.  I'll have a decision to make on what to do with the shield, but is there a consensus (or not) on what to do with the drain wire?

73 N5BCN - Brian

[David Christ]

When I was doing that kind of work the premises wiring was done with
solid but all the jumpers and anything that was plugged and unplugged
regularly was stranded.   The solid was more prone to breaking at the
plug than the stranded was.

Our practice was to have the return of a circuit  paired with the
signal.  For ordinary RS-232 Tx would be on one pair and Rx on
another.  the second wire in each pair would be connected to signal
ground.  Yes, that meant that there were multiple wires running
signal ground.  For things like RS-422  that were balanced, both the
+ and - were always in the same pair.   That was our plant policy.
Jim K9YC can tell us if it was a good policy.  He knows what is best
more than I do.

David K0LUM

At 8:31 PM -0700 6/7/11, Brian - N5BCN wrote:

>Thanks to Don and Jim for their input on building a RFI resistant control
>cable.
>
>I've been informed by another poster that it's recommended to use stranded
>CAT5 or 6 verses solid wire.  The poster believes stranded wire would be
>more resistant to flexing, plugging, unplugging, etc. than solid wire.
>
>One last question on this issue:
>
>I've come across some nice (stranded) CAT6 cable that has a shield and a
>drain wire.  I'll have a decision to make on what to do with the shield, but
>is there a consensus (or not) on what to do with the drain wire?
>
>73 N5BCN - Brian
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Don Wilhelm-4]

  Brian,

Treat the drain wire the same as the shield.  It is just an extension of
the shield.

73,
Don W3FPR

On 6/7/2011 11:31 PM, Brian - N5BCN wrote:

> Thanks to Don and Jim for their input on building a RFI resistant control
> cable.
>
> I've been informed by another poster that it's recommended to use stranded
> CAT5 or 6 verses solid wire.  The poster believes stranded wire would be
> more resistant to flexing, plugging, unplugging, etc. than solid wire.
>
> One last question on this issue:
>
> I've come across some nice (stranded) CAT6 cable that has a shield and a
> drain wire.  I'll have a decision to make on what to do with the shield, but
> is there a consensus (or not) on what to do with the drain wire?
>
> 73 N5BCN - Brian
>
> -----
> K2 #6800 KPA100/KAT100-2, KSB2, KAT2, KIO2, K160RX, KNB2, KAF2, LP-PAN/K2 w/ Pre-amp, SignaLink USB
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/OT-Drain-Wire-on-CAT6-RFI-resistant-cable-tp6452241p6452241.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Jim Brown-10]

On 6/7/2011 9:20 PM, David Christ wrote:
> For ordinary RS-232 Tx would be on one pair and Rx on
> another.  the second wire in each pair would be connected to signal
> ground.  Yes, that meant that there were multiple wires running
> signal ground.

Because RS232 is unbalanced and not impedance matched it is subject to
IR drop on the grounded conductor adding noise to the signal. When that
equipment is plugged into the power line, or when the chassis of one
unit is ground at a different point from the other unit, AC power
leakage currents cause noise voltage to exist between the two equipment
chassis.

This is true of ALL unbalanced circuits, and is why bonding from chassis
to chassis of interconnected equipment is important.  When you bond from
chassis to chassis, you reduce that noise voltage to a very small value.
When you use multiple conductors in parallel for the signal return, you
also reduce the IR drop produced by the noise voltage.

Because RS232 is not an impedance matched system, its bandwidth is
limited by cable capacitance, and noise performance is limited by line
loss, and noise voltage picked up on the signal pair and on the signal
return (the grounded conductor). CAT5 (or 6 or 7) works VERY well for
RS232 because it is very good twisted pair, which minimizes noise, AND
because it has very low capacitance between the conductors of a pair,
which increases bandwidth.

The drain wire that is included with foil-shielded cable is provided so
that a soldered connection can be made to the shield.  Treat the drain
wire as the shield connection -- wire it to the shielding enclosure at
each end.  Use one pair for each signal, and wire the signal return of
each pair to pin 5.

Finally, a reminder about the fundamental value of TWISTING. In the pro
audio world, mic signals are VERY low voltage, and require VERY low
noise pickup to achieve the dynamic range needed for digital audio.
Twisting is FAR FAR more important than shielding in achieving this.
Plain ordinary CAT5 makes excellent audio cable and excellent RS232
cable. I wouldn't lose any sleep looking for shielded CAT5 for my ham
station..

73, Jim Brown K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

[Brian - N5BCN]

If you are near a Fry's Electronics, they sell 25 feet of Cat 6, Shielded Twisted Pair (STP), 26 AWG stranded cable for $9.99.

73 N5BCN - Brian