Cable Modems Cable Broadband Internet Signal loss from serial RG59 cabling - RF amp recommendations?

I currently have cable broadband internet from Comcast. The initial
basic installation was just a wire through the main exterior wall.  I
am leasing a Scientific Atlantic DPC2100 cable modem  from Comcast ( I
am getting about 4Mbps download/ 380 kbps upload currently).

My three floor townhome was built prewired for cable/TV antenna - but
the tv antenna/cable wall jacks were not installed. Recently, I
decided to use the pre existing internal (wall) wiring so I could set
up my  computer upstairs with cable broad band internet connection on
the third floor. So I installed five tv antenna/cable wall sockets/
jacks. I  found out that the house was serially prewired with RG59
dual shielded coaxial wire and that I had to use a 1Ghz two-way
splitter to connect each wall jack. Initially I was able to get an
excellent cable and internet signal from the first(ground/basement)
and second(main)  floor wall jack; however, the third(top) floor wall
cable jacks had very poor cable signal and no internet signal. The
cable signal had apparently degraded signficantly as the length of the
wire increased and the number of splitters increased.   By installing
a Radio Shack RF amp (VCR/TV/FM Variable 20db amp  Catalog No 15-1113)
at the very front of this serial RG59 cable - I was able to boost the
cable signal so that all the cable channels were strong enough to view
clearly on the third floor but it completely blocked the cable
internet signal on every floor. I know that the signal loss is due to
the use of serial prewiring of RG59 and that it would have been better
had the house had prewired with parallel RG6 cables ; but I would like
to avoid ripping up the drywall and rewiring the house from the ground
up.

Is there a RF amp/splitter ( F-connector) that could  boost both the
cable and internet signals?

Walter

On Sun, 20 Jan 2008 07:20:25 -0800 (PST), drydem


Serial wiring? Ouch, what a mess of a bad idea. As you know, the best
thing would be to rewire the entire house with 'home run' cables,
preferably quad shield RG-6 or equivalent rather than RG-59. That's a
lot of work, though.

Barring that, I would add a 2-way splitter where the cable arrives at
the house. One output of the new splitter would connect back into the
house wiring and would power all of the existing TV jacks, and the
other output of the new splitter would connect to a new cable that
would run up the outside of the house to the new office. With this
plan, your new office would have two cable jacks, one for TV and one
for Internet/TV. If necessary, you could still add an RF amp to the
non-Internet side of the new splitter without significantly affecting
the cable modem.

--
Bill

Bill M. wrote:

I agree with everything except the running of the cable outside.  That
would have to be a last resort.  If at all possible, try to find a way
to run it inside if that's what you end up doing.

Another alternative would be to put a decent wireless router at the entry
point and going wireless to the third floor for your internet access.
That would eliminate the need for tearing up your walls or hanging wire
outside the house.


Oftentimes, you can replace parts of your run by just tying one (or even
two cables) to the end of your existing cable and pulling the new cable
through, but that can easily be defeated by staples and such that may
have been used.  You could test that easily enough by just tying some
string to the end of the cable and seeing what happens if you give a bit
of a tug on the next outlet in line and see if the cable runs free.

That would allow you to at least run parallel cables along the serial
route which wouldn't be as short as home runs could be, but the RG6
would make up for the loss due to length over the RG59.

I would think any RG6 or RG11 should be great for longer runs of
non-baseband cable (dual or quad shielded only if you can afford it),
but a CM rated RG59 will handle most of your *short* haul needs with
not much less dB loss than RG6 (in your case with them all strung
together serially, that probably isn't true).

yes.

I thought about that - but I decided
against doing that because of the way the RG59
cable is threaded. The RG59 cable is threaded
from the roof/attic and winds through three
bedrooms (third floor) to the living room ( second
floor) and then drops down into an unfinished
basement(first/ground floor). The attic cable
was put there by the builder to accommodate
an attic TV aerial antenna since a rooftop TV
aerial antennas are banned by the HOA.
Rethreading  the cable is also best done as a
two person job ( one feeding cable, one pulling
the cable).  Given the limited time I have allocated
for this project - I decided that rethreading would
be best for a later project.

Because you failed to use an amplifier with a passive return.



You don't want an amplifier involved with the cable modem at all unles
syour architecture absolutely requires it.   The right way to do it is
to call comcast and have them  do this work properly for you.  If you
dont' want to pay what they might charge an existing customer,  you
might consider cancelling for a few months and signing up again and
gettin the cable modem location and number of activated outlets you
seek in the new customer work order, and it'll probably be free, and
it'll be their problem getting a good cable signal to your cable
modem.

However, I can share what I've learned over 12 years of having a cable
modem.  

You'll want to use a directional coupler instead of a splitter in
front of your cable modem, and feed the cable modem the low-loss
output of the directional coupler.  A DC differs from a splitter in
that the loss on each leg is asymetrical.  It has essentially a
"through" leg that has minimal signal loss (1dB or less) in either
direction and a high-loss "tap" leg that has 6dB loss.

After the DC, on the high loss output, put a quality amplifier, and
then do all your splits for your TV's.    The low-loss output of the
DC goes to the cable modem.  That way your cable modem gets strong
downstream signal and doesn't have anything difficult to push upstream
signal through.  

If you absolutely must have an amplifier in-line with the split that
heads to the cable modem, it must be an amplifier compatible with
cable modems.  Specifically it must be truly bidirectional in
operation, or more typically simply have a passive return path whereby
the upstream cable modem communication can actually pass without
serious degradation.  These amplifiers are somewhat expensive.  I have
2 in my house provided by the cable company though.  The problem with
amplifiers is that they add noise, and cable modems for downstream
data are more sensitive to noise than they are low signal strength.


If you play your cards right,  you can make all this your cable
company's problem.

You may find it far easier, however to keep your cable modem where it
currently works and run either cat5 or 802.11 wireless networking to
your computers.  With access points that can be configured as wireless
clients now costing $40-$60, it becomes hard to justify too many
directional couplers, or even a single bidirectional amplifier.

Best Regards,
--
Todd H.
http://www.toddh.net/