[ARC5] PS Hum in BC-453-B (solved!)

[Brian]

Hello Roy,
Let's be very careful about broad-band, unqualified statements.
Cat-5 cables do not have shielding. When Cat-5 cables are run in ducts 
containing many such cables, all working at 100 MHz plus, eg, between 
computers and servers, then  the shielding associated with Cat-5E has some 
beneficial effect. Computers connected to Cat-5 are almost totally 
insensitive to mains frequencies (50, 60, 100 or 120 Hz). That shield on 
Cat-5E really only works at VHF. At mains frequencies on DC lines, it is 
nowhere near thick enough to have any measurable effect except on your bank 
balance and the country's Gross National Product. The shield may have a 
slight effect at mains frequencies if you use it for such low frequencies as 
on audio level 600 Ohm lines, say, for your home lo-fi. Any good quality EE 
text will wise you up on skin effect - even as far back as the 1st edition 
of Terman (1932). But really, at those frequencies, twisting has the most 
beneficial effect. At DC, twisting has no effect. Any recent text on EMR and 
EMC will help here.

73 de Brian, VK2GCE.

On 01/29/2015 09:07 PM, Roy Morgan wrote:
>
> Note that Cat 5 computer data cable is especially constructed to reduce 
> pickup from external fields.  I think it has 4 pairs of conductors and the 
> shield.  You could run the filament current through two pairs and the B+ 
> through a third pair.
>
> Roy
>   Roy Morgan
> RoyMorgan at alum.mit.edu
> K1LKY Since 1958