[TenTec] OT 75 Ohm twin feeder

[Dr. Gerald N. Johnson]

On Thu, 2008-06-12 at 03:58 -0700, Jim WA9YSD wrote:
> The problem with Lamp cord (Zip Cord), certain speaker cord,  it does not stand up to the sun light, and it is lossy from what I have heard.
> 
Rubber insulated zip cord was the worst for RF loss and for not standing
up to weather and light. I vividly recall a clock starting to smoke one
evening at home when the rubber zip cord fell apart from the warmth of
the clock motor winding (probably over a 25 year period) and the remains
began to conduct and to smoke. Had my mom not noticed the smoke as we
were about to leave for the evening, we might have returned to a big
lump of charcoal.

Its sure that the PVC type plastics in their decorator colors have not
been optimized for RF losses. And there is probably little control
within the wire making industry (especially off shore) as what plastic
and what pigments are used.

> Zip cord as far as I can remember has always been used for speaker cord.

Though there are special wires these days for speaker wire, some with
"special" properties such as more copper, or oxygen free copper (as if
plain copper wiring isn't pretty much oxygen free or it wouldn't meet
conductivity and flexibility tests), and often with clear insulation to
make it easy to tell the tinned from the bare conductor. The special
speaker wire doesn't have to meet a UL standard which ought to make it
cheaper to make, and sometimes it has been cheaper to buy, sometimes
not.

>   Very few lamps these days use it, mostly speaker wire.  UL has been 
> requiring 3 conductor cable cause of the ground wire requirement.
> 
Even in two wire cords, there has been a push at UL to not approve those
with conductors smaller than 16 gauge. In times past especially radios
have sometimes used tinsel conductors that were guaranteed to not trip a
15 or 20 amp breaker or fuse when shorted and those did cause fires when
abused. Many a table lamp was wired with 18 gauge zip cord and the
modern 16 gauge won't pass through its plumbing to rewire it when the
old stuff looses its insulation.


I've not been noticing all that much in small appliances and radios with
three wire cords, but it happens that local jurisdictions can make more
stringent demands than the National Electrical Code and UL require.

>  Keep The Faith, Jim K9TF/WA9YSD
> 
73, Jerry, K0CQ