signal leakage from CATV???
Michael David Kane
installation, he said that he could only activate as many
jacks as we had televisions. The previous owner of the
house has jacks in about every room, but this guy only
activated two of them because we have two TVs. He said
something about signal leakeage or the like, which I don't
buy. Is there a legitimate technical reason for this policy,
or does the cable company just want to get paid for a service
call if we get another TV?
Michael Kane
Paul G. Dupuis
Signal leakage is a constant pre-occupation of cable companies. The
frequency of cable channel 9 (as an example) is the same as your local
broadcaster on VHF channel 9 (pick any local broadcaster channel number as
it applies to your area). If enough cable outlets were not terminated
(i.e. just the connector without a proper terminating resistor or
equipment hooked up to it), your neighbour that doesn't have cable could
have ghosting/interference on his "off-air" channel 9.
It gets worse. I'm not sure about exact frequency allocations in the US
but in Canada, cable companies that want to use channels 41 and 42 are
subject to VERY STRICT regulations. The problem? Channels 41 and 42 fall
in the air traffic band and enough leakage at these frequencies could
cause problems with landing/communications systems.
Not to mention that an unterminated cable will send a reflection down the
cable, causing a ghost (which will vary depending on length of cable).
Leakage is not an invention. The reason cable companies can give you so
many channels is the use of coaxial cable. If the integrity of this cable
is broken, your service will suffer. Other users of these frequencies
will too.
hope this answers your question!
p.s. Does your local cable co charge extra for each additional outlet (monthly
fee, not installation)? If they do, save the money if you're not using
them. If they charge a flat fee per household, go to a local electronics
supply and purchase some 75 ohm F59 terminating resistors (they look
similar to the connectors used for cablevision, with a cap where the cable
would go). Install one on each unused outlet. This will eliminate most
if not all leakage (also called radiation by some companies).
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Paul G. Dupuis "If you fully understand it,
AX640 @ Freenet.Carleton.CA then it must be obsolete!"
Unknown Technoid
PspTP
(Paul G. Dupuis) writes: to Kane....
:If enough cable outlets were not terminated
:(i.e. just the connector without a proper terminating resistor or
:equipment hooked up to it), your neighbour that doesn't have cable could
:have ghosting/interference on his "off-air" channel 9.
>When the cable TV guy came to our house recently for an
>installation, he said that he could only activate as many
>jacks as we had televisions. The previous owner of the
>house has jacks in about every room, but this guy only
>activated two of them because we have two TVs. He said
>something about signal leakeage or the like, which I don't
>buy. Is there a legitimate technical reason for this policy,
>or does the cable company just want to get paid for a service
>call if we get another TV?
>
>Michael Kane
I had a similar experience. I just want to be able to move a tv from one
room to the other. My CATV installer refused to install additional
outlets. Can anyone post the specs for a terminator (something I could
pick up at Radio Shack). The installer also told me the secret CATV
police drive up and down the street picking up violators leaking signal or
unauthorized hookup. BB is watching!
Tim
Don Montgomery
> buy. Is there a legitimate technical reason for this policy,
Both technical and legal. Cable companies pay heavy fines and penalties
for leakage into other services such as aircraft radio, etc. The cable
company wants to do the installation to make sure it is done correctly.
It is possible to activate all the outlets, but they should be terminated
in a 75 ohm type F coaxial load if not used. However, the cable company
doesn't know if the consumer is going to connect a TV to the outlet, remove
the termination and leave it floating, or worse, connect the outlet to his
TV with picture hanging wire.
Ask any radio amateur about channel 18 leakage into the two meter ham band.
- my opinions, comments -
Don Montgomery
do...@sr.hp.com
George Wu
Actually, the cable guy was mostly right, though I'm not sure why
it concerns him. Cable (and antenna) signal strength drops of for each
cabling connection you make, whether you actually hook up that outlet
to a television. So the fewer the activiated connections, where non-
activated outlets are physically disconnected from the cable feed, then
the lower the required amplifier output.
So, here's a general question: How are the amplifiers powered? If
it's powered from the cable line, then I can see why, since every watt
saved means less the cable company has to put out. However, I was under
the impression that the amplifier is normally powered from the house
wiring. In that case, why is the cable person concerned?
George
---
----
George J Wu, Sr. Software Engineer, TRW Business Intelligence Systems
rhodes(n) - unit of measure, the rate at which the same annoying crud is
recycled by newcomers to the net. [ from SunExpert magazine]
Mark Jones
There is a technical reason for this policy, but I'm not sure it's
legitimate.
If all jacks in your house were activated but only a small number of
them had TVs attached to them, you would experience a signal loss.
However, if small terminators were screwed into the unused jacks,
you would experience no signal loss.
These cable terminators are available at Radio Shack for pennies each.
--
Mark Jones Tandem Computers, Inc. ma...@mpd.tandem.com
Austin, Texas
Mark Armstrong soft
>In article <CtJ9F...@freenet.carleton.ca>, ax...@FreeNet.Carleton.CA
>
>>installation, he said that he could only activate as many
>>jacks as we had televisions.
>>something about signal leakeage or the like, which I don't
>>buy. Is there a legitimate technical reason for this policy,
>>
A unterminated connection will act like a attenna which will
pick up the broadcast signal. This is a legitimate technical reason for
this policy.
>
>I had a similar experience. I just want to be able to move a tv from one
>room to the other. My CATV installer refused to install additional
>outlets.
Our cable company operates the same as the phone company,
if you want the cable company to install multiple outlets
in your house, you must pay for each connection. This means
if you have bad reception, the connector comes loose, etc,
the cable company will fix this problem.
It is legal around here to install as many outlets as you
want provided the line drops do not cause problems outside
your house. You pay for the single cable drop and run
your other lines from there. If you have a problem, you should
disconnect your lines and reconnect to a single TV which the
cable company installed. You will be charged by the cable
company if they fix a problem caused by a DIY cabling job.
How to get good reception.
For years I had very bad reception on the local TV channels,
sometimes the ghosts were so bad I needed an antenna.
I first disconnected all my cable runs, I connected the
company wire directly to one TV, no VCR. Still had ghost
so I called the cable company. They ran some new wire
which removed 98% of the ghosting. The installer disconnected
the cable from the TV and put a terminator on the TV. The remaining
2% of the ghost were caused by the TV, it was picking up a small
amount of the broadcast signal from inside the TV. This was the
best I could do without purchasing a new TV (This is a good check
when purchasing a new TV or VCR).
Next, reconnected all my DIY wiring and the ghost were back in full forced.
I removed all my wiring, most of it was cheap Radio Shack wire.
Never buy any wiring from Radio Shack, the cheap stuff is junk, the
good cable is way over priced.
I called my cable company and explained that I was remodeling and
wanted to install some cable runs. They gave me, free of charge, around
200 feet of cable. I had to promise I would only install 3 runs (I ended
up installing 8 runs, each room has a cable connection). I did need
more cable, I priced the "top of the line" cable from Radio Shack,
it was around .50/foot. I called a electrical supply house, they had
some #6 (I forget the proper name, RGU6??) cable for .16/foot. I also bought
a 8 way spliter and some terminators, connectors and a crimping tool.
I needed alot of cable since I installed a single wire from the basement
to each outlet. I could have run one wire upstairs and split it to each
room, but wire is cheap and I have more control of which lines are connected.
I connected 4 of runs (some rooms do not have TVs) with the new cable,
the ghost were still there but not as bad. Next I got rid of all the
small cables used to connect the VCR to the TVs. This helped alot, I
got good reception on clear days but on raining overcast days the ghost
came back.
Going back to the electrical supply house, I bought an amplifier.
I was going to buy a 6 outlet amplifier which they had to order,
cost around $60. They ended up selling me a single outlet amp for
around $20. I connected the cable company wire to the amp which
reduced any chance of signal leakage, from the amp I connected into
the spliter. All unused outlets are terminated.
Finally I get great reception on all channels anywhere in the house.
______________________________________________________________
Mark Armstrong
m...@raster.Kodak.COM
______________________________________________________________
patterson,george r
Michael David Kane <mk...@lamar.ColoState.Edu> wrote:
>When the cable TV guy came to our house recently for an
>installation, he said that he could only activate as many
>jacks as we had televisions. The previous owner of the
>house has jacks in about every room, but this guy only
>activated two of them because we have two TVs. He said
>something about signal leakeage or the like, which I don't
>buy.
Buy it. No cable company is licensed by the FCC to broadcast signals over
the air. Signal leakage brings the company into violation of Federal laws
or regulations. They are required by law to overfly the area (some use
trucks instead) at certain times of the year and check for leakage. The
certified results must be submitted to the FCC. Signal leakage can result
in fines and/or business license revocation.
One major cause of leakage is poorly made connections, usually made for
the purpose of pirating service but sometimes made by a homeowner when
a new TV is purchased. If the level is detectable, the company sends out
service technicians to check every customer connection. This is a major
part of your bill.
I knew one signal pirate a few years ago. The company knew which condo
unit showed leakage, and they'd come by and check the connections every
year (right after their mandatory test), but they had to notify their
customers of the pending visit. The pirate would be warned and would
disconnect the tap for the visit and then hook it right back up. The
company was always in trouble.
-----------------------------------------------------------------------
| If you make $50,000 today [1987], you have the
George Patterson - | same buying power as the average coal miner did
| in 1948, adjusted for taxes and inflation.
| John Sestina (Certified Financial Planner)
-----------------------------------------------------------------------
Andy Green
: In article <CtJ9F...@freenet.carleton.ca>, ax...@FreeNet.Carleton.CA
: (Paul G. Dupuis) writes: to Kane....
: :If enough cable outlets were not terminated
: :(i.e. just the connector without a proper terminating resistor or
: :equipment hooked up to it), your neighbour that doesn't have cable could
: :have ghosting/interference on his "off-air" channel 9.
: Can anyone post the specs for a terminator (something I could
: pick up at Radio Shack).
My 1989 catalog lists the screw-on terminating resistor as part number
15-1144, two for 99 cents. May cost more by now, of course.
Question for anyone: Does terminating unused outlets in this manner net
the same benefit as disconnecting the unused line back at the splitter?
The correct answer for me is hopefully "Yes", since my splitter is up in
the roof... :-(
: The installer also told me the secret CATV
: police drive up and down the street picking up violators leaking signal or
: unauthorized hookup. BB is watching!
Horse hockey. It's all we can do to get them to show up at all when
there is signal trouble. I suspect the most they do is look to see if
there's some unauthorized coax hanging off the telephone pole.
-- Andy
Jim Wall
> them had TVs attached to them, you would experience a signal loss.
> However, if small terminators were screwed into the unused jacks,
> you would experience no signal loss.
>
> These cable terminators are available at Radio Shack for pennies each.
>
> --
> Mark Jones Tandem Computers, Inc. ma...@mpd.tandem.com
> Austin, Texas
Interesting the number of postings that have stated the same thing. This
premise that a video run that ends without a load somehow results in a
loss of signal is not true at all. A loss of signal requires some form
of a load (such as a terminator, or a TV). It is also interesting that
the general consensus is to add a terminator to 'prevent' the loss of
signal. This of course actually increases the loss of signal.
What an unterminated run of cable does is affect the signal quality.
Reflections are generated at the cable end that affect the signal at
other points on the cable run. Depending on the topology of your cabling,
the physical location on that topology, and the characteristics of the
cable you have installed, the signal will vary from twice as strong to
almost completely cancelled.
I know, none of you really care about the black magic part of
electronics, you just want to know what to do. Well, there is no single
correct answer; mostly because everyone does different stuff. Typical
CATV links are brought into a house at one location and are immediately
run to a splitter. The splitter divides the incoming signal to multiple
outputs, and each output usually goes to one and only one CATV jack. In
this situation the end jack could be terminated or unterminated and it
would make no difference to the other jacks. Where people have split off
multiple jacks on a single cable run (without using a splitter) you may
get ghosting or other signal degredations. Or you may not.
Overall, remember that CATV signals are orders of magnitude stronger than
signals that are picked up from Antennas. This is why you able to split a
single CATV input into a dozen cable runs without problems. You want a
single answer? Use passive splitters (any TV store, radio shack, or drug
store should carry them) anytime you add a new CATV run.
-Jim
Number 6
>
>
>In a previous article, mk72...@longs.LANCE.ColoState.Edu (Michael David Kane) says:
>
>>When the cable TV guy came to our house recently for an
>>installation, he said that he could only activate as many
>>jacks as we had televisions. The previous owner of the
>>house has jacks in about every room, but this guy only
>>activated two of them because we have two TVs. He said
>>something about signal leakeage or the like, which I don't
>>buy. Is there a legitimate technical reason for this policy,
>>or does the cable company just want to get paid for a service
>>call if we get another TV?
>>
>>Michael Kane
>
>cable, causing a ghost (which will vary depending on length of cable).
>
>Leakage is not an invention. The reason cable companies can give you so
>many channels is the use of coaxial cable. If the integrity of this cable
>is broken, your service will suffer. Other users of these frequencies
>will too.
>
This is all quite true. I'm talking computer networking here. Has
anyone ever tried running Ethernet (10Mbps) down an unterminated line?
Ethernet is VERY sensitive and runs at frequencies only 10MHz, well
below any TV signals (which start at 62.5MHz for channel 2, as I
recall). I have a little powered amplifier/splitter that has four
outlets for one input. If I don't terminate the ones that are not in
use (the usage goes to three VCR's, one unused) I get terrible
ghosting, unable to receive on any strong broadcast signal in the area
(the interfere so much that the VCR tuner can't discriminate between
the "Cable channel 3" and the broadcast channel 3 and it just shuts
off to the blue screen.) When terminated? No problems.
I'm not really amazed that cable TV works, since it is analog and can
suffer a lot more than digital signals before people complain, but I
am amazed that one can be completely unterminated on a coax with
multiple, parallel (Ethernet in computers is point to point for coax
cable) connections can even work!
Don't ask me about cable companies providing phone service, though! I
have had one dataline (leased, mega$$$$, mega bandwidth) fail for a
couple of days, but have had lots of cable fiascos.
***********************************************************************
Nathan D. Lane, VP Triicon Systems. Lompoc, CA
NaN != 6, 6 == 1. I am not a number, I am a free list!
I'm a programmer my computers are more valuable than my cars.
MIKE CACKOSKI
>From: a...@dlogics.dlogics.com (Andy Green)
>Subject: Re: signal leakage from CATV???
>Date: 28 Jul 1994 15:08:07 -0500
taps. If the cable is not connected to a TV or is shorted (by accident) the
signal will reflect from the open (or short) and set up a standing wave on
the cable system. This delayed wave is what causes the ghost. The standing
wave can upset power amplifiers and draw extra power reducing the
effectiveness of the entire system. A terminator must be plugged onto every
empty cable or tap. Some outlets are built with self terminating
connectors, but most are not. Leakage from an unterminated connection isn'
t strong enough to rebroadcast anything.
Mike Cackoski
St. Paul, MN
patterson,george r
> Actually, the cable guy was mostly right, though I'm not sure why
>it concerns him. Cable (and antenna) signal strength drops of for each
>cabling connection you make, whether you actually hook up that outlet
>to a television. So the fewer the activiated connections, where non-
>activated outlets are physically disconnected from the cable feed, then
>the lower the required amplifier output.
True as far as it goes, but a typical home drop has plenty of spare signal.
They have to put dampers on the drop to bring the signal down to the
proper level. The amps on the customer branch lines have a fixed output
level, so the number of outlets in your home won't alter the amount of
power required to run the amp.
To get an acceptable signal, however, the signal at each outlet in your
home must be approximately a certain level (which I'm too lazy to look
up). So. The technician installs a damper at your home which brings the
drop signal down to the level required for the number of outlets you have.
The outlets are connected in a network using signal splitters. In a simple
example of two TVs, half the signal goes to one and half to the other.
Unplug one TV and you need to cap the line with a 75ohm resistor (as others
have pointed out) to balance things out.
Putting in more splitters requires that the damper be changed to allow
more signal through. Failure to do this will result in poor reception.
In an extreme case, they'd have to change the drop splitter to provide
more power to you. That requires that dampers further down the line be
re-engineered, and things get expensive. If they have to install a
second amp because your house is pulling off too much signal, you can
expect lots of foot-dragging.
> So, here's a general question: How are the amplifiers powered?
Typically they run on commercial power, sometimes using customer house
current. They don't pull much.
>If it's powered from the cable line, then I can see why, since every watt
>saved means less the cable company has to put out.
As stated above, though, the number of outlets doesn't affect the amount
of power the amps require.
>In that case, why is the cable person concerned?
'Cause the FCC will shut them down for broadcasting signals without a
license if there's signal leakage.
-----------------------------------------------------------------------
| If you have a tank which can move and communicate,
George Patterson - | but which cannot shoot, essentially what you have
| is a sixty-five ton portable radio.
| Fort Bragg School of Armour
-----------------------------------------------------------------------
Brian Yuen
>
>This is all quite true. I'm talking computer networking here. Has
>anyone ever tried running Ethernet (10Mbps) down an unterminated line?
>Ethernet is VERY sensitive and runs at frequencies only 10MHz, well
>below any TV signals (which start at 62.5MHz for channel 2, as I
>recall).
[snip]
Not to bust on you too badly, but
MHz != Mbps
Your ethernet receivers like squarish signals with well-defined edges, as
opposed to rounded, sine-wave looking signals. The square part is
composed of harmonics that are a multiple of the changes-per-second
frequency (bps when one pulse == one bit). To get anything resembling a
square wave will require ~7x the bps rate in Hz, so the ethernet really
uses frequencies up to 70MHz and beyond. Proper termination is important
so that signals do not get reflected back and cause false edges/blips to
be detected and interpreted as bits.
In summary, a square wave at 10Mbps eats up much more than 10MHz of
signal bandwidth.
Just hoping to straighten & clarify,
Brian Yuen
FRANK L. Gebhart
I'd like to add my $0.02 to the CATV discussion. About a month ago I was
sitting in my upstairs office when I noticed a truck from the local cable
compant pullup across the street from my house. Several men got out and
proceeded to walk up and down the block with field strength meters
in hand. After a while one came to my door and asked to see my television
installation.
I let him in, we went to the television set in the first floor den and we
both observed that the field strength meter was pinned hard to the right
on the max scale. He looked at the television/VCR/cable hookup,determined
that all was standard, scratched his head and went on his way asking that
I allow a cable company engineer to come the next day to investigate the
situation further.
Two men came the next day and finally solved the problem. It seems that
when the cable was installed, a dual line was run from pole to house
(sides (channels?? modes??)) A and B). At the time only side
A was
active. It was only when the cable company activated channel B that the
interference problem arose. Prior to bringing in the cable my television
was connected to an external antenna on the roof with the usual coaxial
downline. In connecting my televisionm to the dual cable the installer had
disconnected the downline from the antenna and then, for reasons known
only to him, connected channel A to the downline and channel B directly
to the
antenna. No problem until channel B was activated, at which time I became
a satellite transmitter for the cable company. Disconnecting the antenna
and terminating channel B solved the "leakage" problem.
Frank
Jim Wall
> anyone ever tried running Ethernet (10Mbps) down an unterminated line?
> Ethernet is VERY sensitive and runs at frequencies only 10MHz, well
> below any TV signals (which start at 62.5MHz for channel 2, as I
>
> suffer a lot more than digital signals before people complain, but I
> am amazed that one can be completely unterminated on a coax with
> multiple, parallel (Ethernet in computers is point to point for coax
> cable) connections can even work!
Good try, but not a valid analogy. The difference is a broadband system
(CATV) vs. a baseband system (ethernet). Ethernet receivers do not have
any logic to discriminate on frequency bands. There either is voltage, or
there isn't. TV receivers are quite different beasties.
Think of using an antenna, and the entire surrounding community is one
big unterminated cable; reflections everywhere, and it still works. Yes
there are signal reflections from unterminated ends, but the impact is
much, much less critical than an ethernet.
Remember: use a splitter, one CATV jack per each splitter output and you
never need to worry about terminations again.
-Jim
(Maybe I should switch professions to CATV consultant?)
>