US Cable Support > Comcast Cable TV > Upstream noise filter

Upstream noise filter

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.

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?

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.

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....

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

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.

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?

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.

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.

reply to kmand

reply to kmand