Which Cable Connection Scenario, If Any, Is Better?

[tackyjan]

Hello All!!

Can you please tell me which of the following scenarios would be better for connecting my cable modem?

I have one cable line coming into my condo and three devices that require cable (two televisions and a cable modem).
Therefore I have the option of splitting the cable into three using a single three-way splitter (Scenario 1) or two two-way splitters (Scenario 2).

(Note the cable modem in Scenario 2 being connected to the shortest path.)

Assume that all the splitters used in both scenarios have the same properties (frequency range, db loss, etc.).

Thank you!

Jan

P.S. I am currently using Scenario 1, however, I have been having issues with my cable connectivity. The representative at Motorola suggested that, due to low and variant voltage readings coming into the modem, it's probably my splitter. I then went to Radio Shack and an employee suggested trying two two-way splitters (Scenario 2) instead of buying another three-way splitter.

 

[PhilFrisbie]

Scenario 2, using the two-way splitters, will provide the highest signal to you cable modem. I did something similar when my house was wired for my cable modem.

 

[ex_bubblehead]

For starters, NEVER buy splitters at Radio Shack, they're garbage.

Next time you see a cable tech in your neighborhood ask him/her for a couple of 2-way splitters. Even better see if he/she will give you what's called a DC splitter (one side only drops 1db, while the other drops 6.5db). Hook up as in your scenario #2 but put the modem on the 1db side of the DC splitter. That will give you the least signal loss.

 

[tackyjan]

Scenario 2, using the two-way splitters, will provide the highest signal to you cable modem. I did something similar when my house was wired for my cable modem.

The person at Motorola said to pay attention to the following information*:

[Downstream]
Signal To Noise Ratio
- Bonding Channel 142: 36db
- Bonding Channel 141: 36db
- Bonding Channel 143: 36db
- Bonding Channel 144: 36db

Power Level
- Bonding Channel 142: -4 dBmV
- Bonding Channel 141: -4 dBmV
- Bonding Channel 143: -5 dBmV
- Bonding Channel 144: -5 dBmV

[Upstream]
Power Level: 49 dBmV

*My current readings are shown using the two new splitters setup as Scenario 2.

He said to pay special attention to the downstream power level deltas for each of the four channels. If the difference between the highest and lowest value gets above 3 or so the modem may lose connectivity. From what I understood of his explanation it has something to do with the DOCSIS 3.0 protocol. The modem receives multiplexed data on all four channels at once then combines the data as it arrives. If any one channel's power level is significantly less than the other three the modem will have difficulty demuxing the data.

These were my readings before my new setup at the time I called Motorola.

- Bonding Channel 142: -8 dBmV
- Bonding Channel 141: -4 dBmV
- Bonding Channel 143: -3 dBmV
- Bonding Channel 144: -5 dBmV

According to the guy at Motorola these were not good readings. (Note the difference between bonding channel 142 and 143 is 5 dBmV which is significant.)

By chance do you have access to this data? If so, would you mind posting it here so that I can compare yours with mine?

(If you own a Motorola Surfboard modem you can get to it by browsing to 192.168.100.1 using any standard web browser then clicking on the Signal tab.)

Thanks!

 

[tackyjan]

For starters, NEVER buy splitters at Radio Shack, they're garbage.

Next time you see a cable tech in your neighborhood ask him/her for a couple of 2-way splitters. Even better see if he/she will give you what's called a DC splitter (one side only drops 1db, while the other drops 6.5db). Hook up as in your scenario #2 but put the modem on the 1db side of the DC splitter. That will give you the least signal loss.

This is good to know! The guy at Radio Shock told me they didn't make anything better than what they sell. :O Haha.. lies lies lies.. How about Newegg.com? Do they sell good splitters? Have any recommendations (URLs)?

Thanks!

 

[ex_bubblehead]

Downstreams look fine. Upstream is where the problem lies. Motorola modems max out the transmitter at 54dBmv. You want to see that number in the mid 30's to low 40's with a bias toward the lower side.

Edit: Just caught your reply. Your best bet is to get your splitters from the cable company (that's why I mentioned the techs) as they only buy and use the best.

 

[tackyjan]

Downstreams look fine. Upstream is where the problem lies. Motorola modems max out the transmitter at 54dBmv. You want to see that number in the mid 30's to low 40's with a bias toward the lower side.

So my reading of 49 dBmV is high? What could be causing this?

 

[ex_bubblehead]

So my reading of 49 dBmV is high? What could be causing this?

In no particular order:

Bad splitters
Too many splitters between the drop and the modem
Bad fittings
Cable plant problem (most common in my neck of the woods)
Too long a drop
Damaged cable
.
.
.
.
.
.
(Way down the list) Bad modem

All of these require that a cable company tech do an extensive evaluation. You didn't say who your provider is but if it's Cox you should insist that they send out an actual Cox employee rather than one of the contractors that they use (the contractors they use around here are a joke).

 

[tackyjan]

In no particular order:

Bad splitters
Too many splitters between the drop and the modem
Bad fittings
Cable plant problem (most common in my neck of the woods)
Too long a drop
Damaged cable
.
.
.
.
.
.
(Way down the list) Bad modem

All of these require that a cable company tech do an extensive evaluation. You didn't say who your provider is but if it's Cox you should insist that they send out an actual Cox employee rather than one of the contractors that they use (the contractors they use around here are a joke).

My provider is Cox San Diego. I will call them but I don't want to incur a charge (assuming they will charge me since the issue is likely inside my condo).

Curious... how can a high voltage reading be caused by a bad splitter? You would think that too much db drop across a splitter would reduce the voltage not increase it. Unless a bad splitter can also increase the db as well.

Thanks!

 

[ex_bubblehead]

My provider is Cox San Diego. I will call them but I don't want to incur a charge (assuming they will charge me since the issue is likely inside my condo).

Curious... how can a high voltage reading be caused by a bad splitter? You would think that too much db drop across a splitter would reduce the voltage not increase it. Unless a bad splitter can also increase the db as well.

Thanks!

Same neck of the woods. What I said about contractors stands. No way to know it's on your side until the tech looks at it (no charge for looking, only for fixing).

The upstream is so high because the modem is having to literally shout to be heard. All the things I listed cause signal loss that the transmitter has to overcome. Your downstream is good because it starts out high on the street to begin with. It's probably 10 to 12dB higher at the pedestal.

 

[tackyjan]

Same neck of the woods. What I said about contractors stands. No way to know it's on your side until the tech looks at it (no charge for looking, only for fixing).

The upstream is so high because the modem is having to literally shout to be heard. All the things I listed cause signal loss that the transmitter has to overcome. Your downstream is good because it starts out high on the street to begin with. It's probably 10 to 12dB higher at the pedestal.

Thanks for the info! You sound like you really know what you are doing!

 

[ex_bubblehead]

Thanks for the info! You sound like you really know what you are doing!

I contracted with Time Warner Cable in the earliest days of cable modems. Back then the cable techs had no PC or network knowledge so PC techs were teamed with them to perform the PC side of the installation. Very lucrative contract in its day.

 

[tackyjan]

For starters, NEVER buy splitters at Radio Shack, they're garbage.

Next time you see a cable tech in your neighborhood ask him/her for a couple of 2-way splitters. Even better see if he/she will give you what's called a DC splitter (one side only drops 1db, while the other drops 6.5db). Hook up as in your scenario #2 but put the modem on the 1db side of the DC splitter. That will give you the least signal loss.

Here is the URL to the splitter I purchased from Radio Shack:

http://www.radioshack.com/product/index.jsp?productId=12628237

-The 5MHz to 3GHz wideband operation splitter is suitable for digital and analog applications
-Diode-steered provides circuitry protection
-DC power from output ports to input ports without DC back feeding
-Print circuit board provides improved hum modulation and inter modulation performance
-It provides -130dB RFI shielding in solder-back case
-Flat frequency response better for consistent system performance
-Flat-end ports provide superior cable-to-port interface for maximum signal transfer
-Heavy-duty case, gold plating and internal contact pin 24k gold plating @ 2 micro inches thick

The package has a bit more info:

-75 ohm
-DC pass-through

So basically this is garbage?

 

[ex_bubblehead]

Yup. If you were to test them you'd see that they don't even come close to meeting those specs. Cheap Chinese garbage (that's the nicest thing I can say about them).

 

[tackyjan]

Yup. If you were to test them you'd see that they don't even come close to meeting those specs. Cheap Chinese garbage (that's the nicest thing I can say about them).

I am currently on Newegg.com looking for better ones but frankly I don't know how to decide. If you are bored and you come across a website with good quality 2-way splitters would you mind replying with a link?

Here is a good starting point:

http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007088%20600027532&IsNodeId=1&name=Connector%20Splitter


Thanks!!

 

[ex_bubblehead]

Just talk to the cable tech when he/she comes out. They'll just give the splitters to you.

 

[tackyjan]

Just talk to the cable tech when he/she comes out. They'll just give the splitters to you.

Ah ok thanks!