Re: belkin power conditioner for my Samsung LCD - is it worth it???

On Mon, 20 Aug 2007 18:33:03 -0700 w_tom <w_tom1@xxxxxxx> wrote:

| How large is potential difference between a coax shield and its
| center core? For example an IEEE paper maybe a generation ago at Camp
| Blanding FL studied a buried power coax cable - an example where the
| shield was very poor. Current in the shield was 41 times higher than
| a current in the center core that was only 0.06 amps. Coax cables
| for data (ie TV) have one shield layer that is massively better - and
| then a second shield layer. Both shields mean surge currents in the
| center core are even less.

This doesn't make any sense. Coax can carry a _lot_ more current than
that. It can carry massively _huge_ amounts of current if you don't
mind destroying it in the process.


| Cited was thousands of volts for an RG-6 cable - that ignored the
| relevant parameter - leakage resistance. Current is the important
| parameter. Voltage is a dependant variable. Even a coax cable with
| near zero shielding has trivial surge current in its center core. And
| then we existing is but another layer of protection.

Voltage is important when dealing with differential mode. If a surge
is in common mode up to a point where the shield is connected solidly
to ground via a short wire, from that point on it can be mostly
differential mode. The voltage that would be developed with depend
on the current, of course. But the maximum voltage you could get is
the voltage the insulation would still hold back against a breakdown.


| Both cable ends (cable amp and TV receiver) must have protector
| circuits that make even that trivial center core current irrelevant.
| Ever static electric discharge into a radio antenna? Radio was
| routinely destroyed? Of course not. How did up to 20,000 volt
| discharge not harm the radio? Because even radio front end RF amps
| have significant protection. Even early 1960 transistorized CB radios
| made such surges irrelevant using only an NE-2 neon glow lamp.

My first experience with lightning destroying a radio was when I was
about 13 years old. I was listening to a portable radio inside during
a thunderstorm. The telescoping antenna was up about 2 feet long.
A lightning strike occurred at the far end of the back yard, which was
about 80 or 90 feet away. The radio just went dead and never worked
again, other than being able to produce some hiss to the speaker at
full volume.

Such protection is not routinely in radios. I can't say there is no
radio that has it. But none of the dozen or so I have taken apart
had any.


| Piggy's cable guy is completely correct. That earthed cable
| provides the protection. A $90 belkin is only recommended because it
| is called a protector. If it is called a protector, then it will
| protect from floods? Junk science reasoning. Why would it
| supplement protection when it does not even claim any such
| protection? If it is called a protector, then does it also protect
| from floods? To provide supplementary protection from a surge that
| seeks earth ground, then either is must stop that surge ($hundreds
| series mode protector) or it must earth. Those are the only two
| options.

Earthing only the shield of the coax and providing no other protection
is only partial protection of the coax.

BTW, I'm tiring of this repetition. We don't 100% disagree or 100%
agree. It appears we shall have to leave it at that. It takes quite
some time to post these extensive replies, and we aren't getting anywhere
at all with this.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-08-20-2208@xxxxxxxx |
|------------------------------------/-------------------------------------|
.

Relevant Pages

  • Re: belkin power conditioner for my Samsung LCD - is it worth it???
    ... Of course coax can carry more current. ... Even a coax cable with minimal and leaky shielding permits minimal ... Then both ends of that cable have surge protection. ... Just because one radio fails means ...
    (alt.tv.tech.hdtv)
  • Re: belkin power conditioner for my Samsung LCD - is it worth it???
    ... Of course coax can carry more current. ... Cable TV cable has better shielding. ... If radios do not routinely contain RF amp protection, ...
    (alt.tv.tech.hdtv)
  • Re: Satellite antenna grounding
    ... I don't see the isolation of the shield at the receiver as necessarily being ... since the geometry of the dish will not make it an effective ... Also, it appears to be a code violation to me, if the coax ... Antenna installers seem to be better about it, ...
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  • Re: belkin power conditioner for my Samsung LCD - is it worth it???
    ... |> | Blanding FL studied a buried power coax cable - an example where the ... |> | shield was very poor. ... |> | a current in the center core that was only 0.06 amps. ... | Phil I know very little about "buried power coax cable", why design ...
    (alt.tv.tech.hdtv)
  • Re: FIGHT! FIGHT! FIGHT!
    ... I know that a coax cable does not radiate (if common mode currents properly suppressed) because both conductors are apparently "in the same place". ... Current and fields penetrate only a very small distance from the inner surface of the shield, and no significant amount ever makes it through to the outside. ... The capacitive coupling to the braid is much higher than the coupling to the inner conductor. ...
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