kmand
join:2002-05-06
Decatur, GA
| Upstream noise filter
More than 10 years ago when all I had was a TV, there was a TNB6-40P8/10 (an upstream noise filter) standard on each output of the outdoor distribution box that the Cable company used to feed my Condo (a multi apt building).
When I got my cable modem, the technician split the feed in my unit and moved the filter indoors to the TV side.
A lot has changed in 10 years. The Cable company has changed hands a few times and is now Comcast, and a lot of engineering changes have been made in the system. On the TV side of my split I added a bidirectional amplifier since I now have a lot of active taps including some bidirectional cable boxes and the signal level was too low with all the splitting. The filter sits right at the first split before the amplifier.
I don't know if the filter was ever needed, and if its helping or hurting anything now. I'm inclined to remove it just to have one less item in line with what is already too many items on one side of the split. I guess in theory an upstream filter shouldn't cause any loss on the downstream side, but thats in theory. Is removing it a bad idea?
Also, if Comcast/Tivo ever gets to my area won't this filter kill the DOCSIS return channel that the Comcast/Tivo/Motorola boxes use? The Motorola box doesn't use the built in Docsis modem with the legacy DVR software. |
|
dishrich
join:2006-05-12
Springfield, IL
edit:
February 19th, @03:38PM
| Well I gotta ask this question - if you are using bidirectional cable boxes on the TV side, HOW are they working now, since normally when the headend does not get a response back periodically from those boxes, they get deactivated as non-responders. (or so is my understanding)
But actually, that filter WILL cause problems with any of the digital cable boxes, since they also use that upstream band to communicate back to the headend - again, they will normally shut down if they are unable to do so.
Insight here did it the same way, including putting return filters on all splitter legs that just connected directly to the TV. But, they now NO longer use these at all, not even on basic TV only subs. But, I still use one on the splitter leg that goes to my TV's, since I am combining it w/modulated in-house channels, just to be a little safe. |
|
kmand
join:2002-05-06
Decatur, GA
| The upstream frequency on the Comcast/Iguide boxes is 10.976. The TNB6-40P8/10 is an 8-10MHZ upstream noise filter. I'm not exactly sure what it does to the 8-10mhz range, perhaps block it entirely? However, it seems to be just below the 10.976.
As I said this was installed 10 years ago, and I don't know what it was trying to protect then, and what it would protect now. What uses 8-10mhz? |
|
Agent 86
@comcast.net | reply to kmand
It's passing 8-10Mhz, not blocking 8-10Mhz. I guess the point was to allow set top boxes to communicate, while keeping the spectrum used by cable modems clean. |
|
gar187er
Premium Alcoholic
join:2006-06-24
Dover, DE
edit:
February 21st, @03:10PM
| reply to kmand
dont remove it.....all you need to do is take that off, and inject massive noise onto your node and throw an alarm......
it stop interference from entering the cable lines.... |
|
ccna90210
@rcn.com
| reply to kmand
even though your system probably changed hands many times, the techs tht work there are still the same. that is called a "high pass window filter"...high pass meaning it passes high frequency meaning foward signal 50-860mhz. it blocks 6-40mhz which is return path frequencies BUT allows 8-10mhz to pass.
moto digital boxes send a signal back on 8.09mhz
like gar187er said, dont remove it
said by kmand  :More than 10 years ago when all I had was a TV, there was a TNB6-40P8/10 (an upstream noise filter) standard on each output of the outdoor distribution box that the Cable company used to feed my Condo (a multi apt building). When I got my cable modem, the technician split the feed in my unit and moved the filter indoors to the TV side. A lot has changed in 10 years. The Cable company has changed hands a few times and is now Comcast, and a lot of engineering changes have been made in the system. On the TV side of my split I added a bidirectional amplifier since I now have a lot of active taps including some bidirectional cable boxes and the signal level was too low with all the splitting. The filter sits right at the first split before the amplifier. I don't know if the filter was ever needed, and if its helping or hurting anything now. I'm inclined to remove it just to have one less item in line with what is already too many items on one side of the split. I guess in theory an upstream filter shouldn't cause any loss on the downstream side, but thats in theory. Is removing it a bad idea? Also, if Comcast/Tivo ever gets to my area won't this filter kill the DOCSIS return channel that the Comcast/Tivo/Motorola boxes use? The Motorola box doesn't use the built in Docsis modem with the legacy DVR software. |
|
cypherstream
There's no place like 127.0.0.1
join:2004-12-02
Reading, PA
clubs:
 ·Cingular Wireless
edit:
February 23rd, @12:12PM
| reply to kmand
Yup our boxes return on 8.096 MHz. I guess it has a small window to xmit on, because another provider in the area using Moto boxes xmit on 10 or 11 MHz IIRC.
As far as downstream our boxes read OOB data on 104.2 or 104.5 (Can't remember exactly), and the other providers reads OOB data on 75.25 MHz.
I'd rather have them reconfigure our system to read OOB on 75.25 MHz, because reading it at the 104 MHz frequency effectively knocks out channel 97 from being used for anything (Analog or Digital).
I heard that some older Moto boxes had the frequencies hard coded, so if they are out in the field I guess they cannot change the OOB and return frequencies in our system. The newer Moto boxes are more agile and have a 10 frequency channel selection that they "Hunt" for OOB for, then the OOB tells the box what freq. the return channel is on. |
|
kmand
join:2002-05-06
Decatur, GA
| I went back and read the diag menus again on my Comcast/Motorola DVR DCH3416 and it deos indeed have OOB at 75,25mhz, above the 60MHZ limit of the filter.
However, it also clearly lists under upstream status "center frequency 10.976 mhz". Why wouldn't that be blocked since its above 10 and below 60? |
|
MadMANN
Premium
join:2005-08-19
 ·Comcast
edit:
February 23rd, @06:27PM
| reply to kmand
I worked in a few systems where they would throw those HP filters on any line that didn't have equipment on them. It wasn't necessarily because the TV or cabling was throwing noise back into the line, but it was a preventative action.
The system that I am in now is an "open" system, meaning that they do not want any HP filters anywhere for the purpose of self-installs. They want us to fix the cause of the actual problem if there is one and remove any HP filters you see from the old cable company. If we find a leak and the customer is not home, we are now given some varied value 5-54mhz pads to use in lieu of the HP. That way, the return still works, but the noise is attenuated until we can get inside the home.
All that said, if your cabling inside your home is contained, meaning you have good connectors everywhere and well shielded cables, the removal of that filter likely would not affect anything. However, if it is questionable, it would be best to leave it until you have the problem fixed. |
|
Agent 86
@comcast.net
| reply to kmand
"However, it also clearly lists under upstream status "center frequency 10.976 mhz". Why wouldn't that be blocked since its above 10 and below 60?"
It's close enough to the pass band. Filters don't have an infinitely sharp slope.
As MadMann said, the filter is just a precaution and most cable systems don't use them. Removing it won't hurt anything. |
|
codee
Premium
join:2001-10-01
Minneapolis, MN
·Sprint Mobile Broa..
| reply to kmand
said by kmand :I went back and read the diag menus again on my Comcast/Motorola DVR DCH3416 and it deos indeed have OOB at 75,25mhz, above the 60MHZ limit of the filter. However, it also clearly lists under upstream status "center frequency 10.976 mhz". Why wouldn't that be blocked since its above 10 and below 60? The OOB is the frequency that the box gets all its data from the headend on. Whenever there are guide updates, softeare updates, etc they all get broadcasted over that 75.25 freq. 55Mhz and up is the forward so if you blocked that you would lose some analog video as well. |
|
toolman1955
join:2008-03-02
Pendleton, IN
| reply to kmand
said by kmand :A lot has changed in 10 years. The Cable company has changed hands a few times and is now Comcast, and a lot of engineering changes have been made in the system. On the TV side of my split I added a bidirectional amplifier since I now have a lot of active taps including some bidirectional cable boxes and the signal level was too low with all the splitting. The filter sits right at the first split before the amplifier. I don't know if the filter was ever needed, and if its helping or hurting anything now. I'm inclined to remove it just to have one less item in line with what is already too many items on one side of the split. I guess in theory an upstream filter shouldn't cause any loss on the downstream side, but thats in theory. Is removing it a bad idea? Removing it is a bad idea. If you have a bi-directional amp in-line because you have added several more outlets yourself inside chances are you have alot of ingress in your CONDO and if you remove the filter you will amplify the ingress problem back out onto the plant and cause problems for all. |
|
