Re: Cable Broadband Internet Signal loss from serial RG59 cabling - RF amp recommendations?
- From: comphelp@xxxxxxxxx (Todd H.)
- Date: 22 Jan 2008 11:17:54 -0600
drydem <walter_lee@xxxxxxxxxxx> writes:
Thanks for the tip.
I went to the local Radio Shack store and I purchased
a Bi-Directional Cable TV 10db Amplifier (Radio Shack Catalog
Number 15-2505) which is designed to allow for digital cable
modems, digital TV, and pay for view services. I replaced
the older RF 20db Amplifer with the newer Bi Directional
RF 10db Amplifier - while the cable channel signals were still
usable/powerful -- the cable modem was still unable to
get an internet broadband signal in the office. Why didn't
it work? I'm not sure.
There are a few possibilities. You're (admittedly) using the wrong
cable, you're crimping your own connections, using a Radio Shack
amplifier and a Home Depot 3-way splitter. It's amazing you get TV
much less cable modem signal. :-)
May I suggest a more methodical approach?
Let's start by plugging the cable modem in where it last worked. Look
at the web page at http://192.168.100.1 where most DOCSIS modems will
have a signal page somewhere... and record upstream power level,
downstream power level, and signal/noise ratio (SNR). Post those
results. Then we'll know how much margin you have to play with. For
example, right now I'm looking at -8.5dBmV downstream (a bit whimpy
but ok), 49.25dBmV upstream (pretty high... this is how much the cable
modem has to crank up the gain to get a signal to the head end), and
34dB SNR (solid). This trio is on the edge of reliability, in my
experience. Ideally I'd like downstream a little higher, upstream a
little lower, and SNR the same or, heck, higher is always good for
SNR.
Next, add in the 3 way splitter without moving the cable modem from
that physical location. Load the 3 way splitter with 2 legs hooked to
something that terminates the line so we dont' worry about reflections
and such, and repeat the test with the cable modem hooked into the 3
way splitter right there in front of you. This eliminates wiring
losses and sees if the splitter itself is garbage (which it may be
given its purchase at a building supply store). Visit that diagnostic
web server in your cable modem again, record those power levels and
SNR and post here.
Now move the cable modem down to the end of the line. If the modem
will give you any signal levels there despite its inability to sync,
record those. This will help narrow doewn where the problem is.
Currently I have the source cable line (from the exterior wall)
connected to a 2Ghz 3 way digital splitter (Ideal from Home
Depot). The Main Splitter output line #1 goes to the cable modem
That's good-there's no amplifier between your cable modem and the head
end. But you can do better.
You'd probably get nearly a 6dB improvement if you throw away that
3-way digital splitter, and replace it with 2 items:
a directional coupler. A very high quality one is
Antronix CMCDT2109T but I've also seen CMCDT2106T.
a 2-way splitter rated for sufficient bandwidth. Antronix
CMC3000H OR equiv.
You won't find these at radio shack, but I bet your cable company has
em.
House feed comes into the directional coupler, through output goes to
cable modem, tap leg goes to 2-way splitter which then feeds your main
floor tv, and that whole mess of serially connected stuff
respectively.
( for this computer I am using now), the Main Splitter output line#2
goes to a cable ready TV (main floor) which I am using to
monitor the initial cable signal, the Main Splitter output
line#3 goes to the RF amplifier which power the rest of
the cable wall jacks via the serial RG59 cable. Behind this
RF amp there are five 1Ghz two way splitters(Ideal) that
are connected serially from closest to farthest away:
Splitter#1:Basement Fconnector, Splitter#2:LivingRoomWallOutlet,
Splitter#3: MasterbedroomWallOutlet, Splitter#4: OfficeWallOutlet,
Splitter#5: GuestroomWallOutlet. From the guest room, the
cable goes up into the attic where part of it is stapled to one
of the rafters (so you can find it). I am using a DataShark
TV-Cable crimping toolkit to make the connections.
Don't try to swing for the fences just yet. Build up the distribution
system slowly and test the cable modem and gather data at each step of
the way. You've got a rather complicated setup, and cable modems
are finicky.
Best REgards,
--
Todd H.
http://www.toddh.net/
.
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