[NTLUG:Discuss] APC UPS XS1500 question

[Darin W. Smith]

On Wed, 30 Jul 2003 06:26:39 -0500, fredjame <fredjame at concentric.net> 
wrote:
> There used to be available, and perhaps still is, a small barrel shaped, 
> inline device for protecting coaxial cable from power surge (dimensions 
> about 1x3 inches, I think).  It will reduce the length of cable allowed 
> (i.e., it cuts signal strength), and may change or introduce noice.  I 
> used one for a while years ago, but as the length of the cable grew to 
> include another building I had to remove it (we were using coax to 
> connect a server to several terminal servers in a dumb terminal 
> environment).

Radio Shack has a little inline device that also has a ground wire.  It 
uses a neon bulb inside to shunt surge to ground.  Not the best idea, as 
then the surge will probably get back into other nearby devices through the 
chassis ground...but for small surges it is probably effective and not too 
much trouble.  I'm using one.  It's cheap.  They have a similar ethernet 
"protection" device.

Also, on your standard surge protectors, be careful about the "Ant/Cable" 
protection.  You need something that will pass stuff in the 1 Ghz band for 
your cable modem to work.  The simple solution is to use the jacks labeled 
"SAT"--as in Satellite--as DBS systems go up to 2.2Ghz on the wire.  As I 
recall, the DOCSIS standard puts upstream stuff around 60Mhz (between 
standard "analog" cable channels) and downstream (incoming) stuff up around 
1 Ghz.  This is how they physically cap your outgoing bandwidth, while 
allowing much faster download speeds.  The side effect is that it then 
becomes difficult/expensive to block the standard analog cable channels 
while still allowing data services (but if you read your service agreement, 
you will see that unless you are paying for the priveledge of viewing those 
analog TV signals, the cable company defines it as theft-of-service).  The 
silly thing is, if you inquire, most cable companies have a "package deal" 
that charges you something like $3 a month for the analog TV, and drops 
your total bill by $2 a month because you are subscribed to multiple 
services (or maybe once had--it really depends on the customer service rep 
you get--most will try to make you think you have to pay for some minimum 
digital package or something--I guess they work on commission and are 
trying to beef up their own earnings).  So the cost to be legal if you want 
to use those TV channels is about $1 a month--really a pretty good deal.  
One could argue that since they have to provide that signal anyway, they 
should just figure that into their cost of service in the first place and 
drop the whole "theft-of-service" bit...just make the analog TV channels a 
"feature" of the data service--that would eliminate all their whining about 
"the analog loophole" and "analog piracy"...but some folks--especially big 
media conglomerates--like to whine.

As for grounding, just be sure you have a good quality grounding block 
where the cable enters your residence.  Make sure it is properly bonded to 
a good ground, such as the cold water pipe, a copper grounding rod, the 
conduit on the electrical service entry, etc.  The cable company should 
have installed this for you.  They put a really good one on mine.  They 
should also have used weatherproof snap-n-seal connectors and coated it all 
with dielectric grease.

The one aspect where a lot of folks mess up when grounding coax is to have 
the signal lead (the copper in the center of the cable, in the center of 
the connector) too long.  It should only extend about 1/16" beyond the end 
of the connector.  If both leads are too long going into the grounding 
block, they will make contact with each other and the only thing the 
grounding block will do is provide the termination for the shield (which is 
necessary for the shield to have any effect anyway).  The grounding block 
is supposed to provide a gap between the signal leads to be coupled.  The 
center conductor is not directly shorted to ground (obviously that would 
destroy the signal), but the gap is used to continuously bleed off a static 
charge before it reaches dangerous levels.  It is important to realize 
then, that the grounding block is not at all intended for lightning 
protection.  It is for small static surge protection.  It is more of an 
isolator between the two wires.  It is also important to note that this 
means it will have an insertion loss--as it is a passive element.  Usually, 
the insertion loss is stamped on a device somewhere.  High quality 
grounding blocks will have very minor impact on the signal strength--much 
less so than passive splitters (which usually have on the order of 3dB 
insertion loss).

-- 
D!
Darin W. Smith
AIM: JediGrover
"If you pick up a starving dog and make him prosperous, he will not bite 
you. This is the principal difference between a dog and a man." --Mark 
Twain "Pudd'nhead Wilson's Calendar"