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

Cable Broadband Internet Signal loss from serial RG59 cabling - RF amp recommendations?
NewsGroups | Search | Tools
User Password
Register Now! Lost Password?
 comp.dcom.modems.cable  Post an article  get this group's latest topics as an RSS feed add this group's latest topics to your My MSN content add this group's latest topics to your My Yahoo content  add this group's latest topics to your Google content  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
Cable Broadband Internet Signal loss from serial RG59 cabling - RF amp recommendations? drydem 01-20-2008
Posted by Todd H. on January 22, 2008, 12:17 pm
If you were  Registered and logged in, you could reply and use other advanced thread options

> 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/

Posted by drydem on January 23, 2008, 7:10 pm
On Jan 22, 12:17=A0pm, comph...@toddh.net (Todd H.) wrote:
> > 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. =A0I replaced
> > the older RF 20db Amplifer with the newer Bi Directional
> > RF 10db Amplifier - while the cable channel signals were still
> > usable/powerful -- =A0the cable modem was still unable to
> > get an internet broadband signal in the office. =A0Why didn't
> > it work? I'm not sure.
>
> There are a few possibilities. =A0You're (admittedly) using the wrong
> cable, you're crimping your own connections, using a Radio Shack
> amplifier and a Home Depot 3-way splitter. =A0It's amazing you get TV
> much less cable modem signal. =A0:-)
>
> May I suggest a more methodical approach?
>
> Let's start by plugging the cable modem in where it last worked. =A0Look
> at the web page athttp://192.168.100.1where most DOCSIS modems will
> have a signal page somewhere... and record upstream power level,
> downstream power level, and signal/noise ratio (SNR). =A0Post those
> results. =A0Then we'll know how much margin you have to play with. =A0For
> 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). =A0This trio is on the edge of reliability, in my
> experience. =A0Ideally I'd like downstream a little higher, upstream a
> little lower, and SNR the same or, heck, higher is always good for
> SNR.

That's an excellent idea. Thanks.
Since this network cable is a serial - I can measure
the signal from the external wall source to each connection
point to determine if there is any radical loss of power.

using the Webstar dPC2100 cable modem as a
network diagonistic tool is an excellent idea
thanks. The Webstar dpc2100 cable modem status
on ip address 192.168.100.001 has a receive
power and transmit power level. Because my old
old 20db RF amplifier is a unidirectional I
remove it for the following reading. Reading
from the source signal down the line I found
that by the time I get to third floor in the
master bedroom I have a dramatic loss in my
ablity to transmit a signal. I suppose I could
redo this wall socket and see if that helps...

here are my readings:

1) Original Comcast Cable Signal(RG6 cable via compressed Fconnector)
Recieve Power -05.2 dBmV
Transmit Power +42.0 dBmV

2) Signal passes through Ideal 2Ghz 3-way digital/Satellite Splitter
Recieve Power -02.2 dBmV
Transmit Power 47.0 dBMv

3) Signal passes through Ideal 1Ghz 2-way splitter in Basement
Receive Power -07.3 dBmV
Transmit Power 52.0 dBMV

4) Signal passes through Ideal 1Ghz 2-way splitter to Living Room
Cable TV outlet
Recieve Power -13.5 dBmV
Transmit Power 55.5 dBmV

5) Signal passes through Ideal 1Ghz 2-way splitter to Master Bedroom
Cable TV Outlet
Recieve Power -17.7 dBmV
Transmit Power 008.3 dBmv --- ouch!


The last reading is really pathetic - give to drastic drop in
signal the office or guest room connection must be getting zilch.

I was experimenting with those fancy twist on RG59
f-connectors in the master bedroom... it looks like I am
going to have to redo that wall socket as a crimp f-connector
instead...



> Next, add in the 3 way splitter without moving the cable modem from
> that physical location. =A0Load 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. =A0This eliminates wiring
> losses and sees if the splitter itself is garbage (which it may be
> given its purchase at a building supply store). =A0Visit 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. =A0If the modem
> will give you any signal levels there despite its inability to sync,
> record those. =A0This 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. =A0 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:
>
> =A0 =A0 =A0 =A0 a directional coupler. =A0A very high quality one is
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Antronix CMCDT2109T =A0but I've also seen =
CMCDT2106T.
> =A0 =A0 =A0 =A0 a 2-way splitter rated for sufficient bandwidth. Antronix
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 CMC3000H =A0OR equiv.
>
> You won't find these at radio shack, but I bet your cable company has
> em.


Yes.
Radio Shack and Home Depot have only the basics.
If my cable company has them they aren't selling them to DIYers like
me
=2E

>
> 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) =A0which 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. =A0Build up the distribution
> system slowly and test the cable modem and gather data at each step of
> the way. =A0 =A0You've got a rather complicated setup, and cable modems
> are finicky. =A0
>
> Best REgards,
> --
> Todd H.http://www.toddh.net/


Thanks for all the help!

Posted by Todd H. on January 23, 2008, 7:33 pm

> On Jan 22, 12:17 pm, comph...@toddh.net (Todd H.) wrote:
> > > 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 athttp://192.168.100.1where 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.
>
> That's an excellent idea. Thanks.
> Since this network cable is a serial - I can measure
> the signal from the external wall source to each connection
> point to determine if there is any radical loss of power.
>
> using the Webstar dPC2100 cable modem as a
> network diagonistic tool is an excellent idea
> thanks. The Webstar dpc2100 cable modem status
> on ip address 192.168.100.001 has a receive
> power and transmit power level. Because my old
> old 20db RF amplifier is a unidirectional I
> remove it for the following reading. Reading
> from the source signal down the line I found
> that by the time I get to third floor in the
> master bedroom I have a dramatic loss in my
> ablity to transmit a signal. I suppose I could
> redo this wall socket and see if that helps...
>
> here are my readings:
>
> 1) Original Comcast Cable Signal(RG6 cable via compressed Fconnector)
> Recieve Power -05.2 dBmV
> Transmit Power +42.0 dBmV
>
> 2) Signal passes through Ideal 2Ghz 3-way digital/Satellite Splitter
> Recieve Power -02.2 dBmV
> Transmit Power 47.0 dBMv

This reading doesn't make sense. It's 3dB higher than the original.
Which leaves us wondering how we got 3dB of gain by going through a
3-way splitter. Something is wonky.

> 3) Signal passes through Ideal 1Ghz 2-way splitter in Basement
> Receive Power -07.3 dBmV
> Transmit Power 52.0 dBMV

Yer on the edge of the cable modem working without packet loss at this
point.

> 4) Signal passes through Ideal 1Ghz 2-way splitter to Living Room
> Cable TV outlet
> Recieve Power -13.5 dBmV
> Transmit Power 55.5 dBmV

And transmit is probably maxed out at this point. Cable modem
probably wont' sync here.

> 5) Signal passes through Ideal 1Ghz 2-way splitter to Master Bedroom
> Cable TV Outlet
> Recieve Power -17.7 dBmV
> Transmit Power 008.3 dBmv --- ouch!

Transmit opwer obviously something strange here. but with 55 being
the max most modems will try to push, weird readings here don't pahse
me On the receive end, which is all you care about because it's a TV
line for ya, you're seeing the same 6dB drop you've seen after prior
2-way splitters. 3.5dB is the nominal insertion loss of a 2-way
splitter, but the cable modem may be testing at a relatively high
ferquency that sees more loss than nominal. Cable losses also
contribute and are frequency dependent.


> The last reading is really pathetic - give to drastic drop in
> signal the office or guest room connection must be getting zilch.

Nah, it's not really that bad. Does the TV work there? Of course the
modem work as it's out of the upstream gain range.

> I was experimenting with those fancy twist on RG59
> f-connectors in the master bedroom... it looks like I am
> going to have to redo that wall socket as a crimp f-connector
> instead...

The twist on's yeah... I seemt o recall them being a trouble spot.


--
Todd H.
http://www.toddh.net/

Posted by $Bill on January 23, 2008, 7:59 pm
drydem wrote:
>
> Yes.
> Radio Shack and Home Depot have only the basics.
> If my cable company has them they aren't selling them to DIYers like
> me
> .

When I added internet to my cable, they came out and added a grounding
block, grounded it to my AC distro panel, put new terminators on my
RG59 home runs and installed a new 1:4 splitter. I asked them for a
75-100' cable so I could later run it myself through the ceiling to my
cable modem and they whipped up a cable, tested it and handed it to me.

They'll pretty much give you whatever you need if you ask nice has been
my experience.

Posted by Todd H. on January 24, 2008, 12:00 am

> drydem wrote:
> >
> > Yes.
> > Radio Shack and Home Depot have only the basics.
> > If my cable company has them they aren't selling them to DIYers like
> > me
> > .
>
> When I added internet to my cable, they came out and added a grounding
> block, grounded it to my AC distro panel, put new terminators on my
> RG59 home runs and installed a new 1:4 splitter. I asked them for a
> 75-100' cable so I could later run it myself through the ceiling to my
> cable modem and they whipped up a cable, tested it and handed it to me.
>
> They'll pretty much give you whatever you need if you ask nice has been
> my experience.

Agreed.

Since cable companies don't really know how to respond to change
requests for existing customers, one tack for Drydem to take is to
move the cable modem to an outlet where it doesn't work, then call in
a service request indicating it's not working to the point they send a
technician out, and they'll get you squared away generally, applying
DC's appropriately as needed.

Dunno how many if any cable companies actually track where in your
home they installed the modem. The tech onsite will see that you made
your own ends perhaps, and that the cable might be wrong, but they
also might assume that the original installer didn't want to deal with
running new cable and that the homeowner might not have had anything
to do with it. Applying the right level of "I'm not sure what's going
on, but I'm hoping you can help make it work" along with being affable
generally gets you in a better place by the time the tech leaves.

"I moved my office, and needed the cable modem in this room, and
thought it was like DSL at my other office where I could just move the
the box to any other jack in the house."

the cable company won't want to make too big a deal of how cable modem
technology is more finicky than DSL, and they'll most likely do what
they can to make it work where you want your modem. They'll install
quality directional couplers and splitters and remake ends with high
quality crimp connections until it works, generally.

One thing to watch out for and not underestimate: tight cable bends.
I had a tight 90 degree cable bend back in a wall jack that turned out
to be the culprit of 9 friggin dB of signal loss. I couldn't believe
it myself. STraighted it out, redid the end and voila.

--
Todd H.
http://www.toddh.net/

Similar ThreadsPosted
ADC Multimodem 701g (mm701g) Serial Cable Schema August 9, 2005, 1:32 pm
wireless router cable modem recommendations? July 30, 2005, 8:59 pm
Trying to split a cable signal ... May 19, 2008, 2:40 pm
cable modem signal issues, and how they were resolved November 29, 2006, 12:13 am
Modem Keeps Dropping Signal December 15, 2005, 1:02 am
Splitting a coax signal September 10, 2006, 11:24 am
Acceptable signal strength? July 7, 2008, 7:10 pm
Moto signal level code November 22, 2005, 10:14 am
Moto SB5100 signal drop April 21, 2006, 10:36 pm
NTL cable broadband affects BT phoneline? October 19, 2005, 1:57 pm

other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

Custom CGI Perl and PHP programming by 1-Script.com

Contact Us | Privacy Policy
The site map in XML format XML site map