Coax filter

If it goes to the TV, it is a high pass filter to keep the uplink RF from overloading the TV. Some tuners have no internal filtering, and broadband causes problems.

I see ... What frequencies are used for the TV and the broadband?

I can think of several possibilities.

It might be a narrow-band "reject" filter, to block the strong "upstream" backchannel signal being transmitted by your cable modem before this signal reaches and affects your TV. A strong signal of this sort could overwhelm the tuner in your TV, causing interference or picture dropouts when your cable modem is transmitting.

It might be a high-pass filter which blocks DC and low-frequency AC, to break up any possible "ground loop" which might occur if your TV and cable modem are plugged into different power circuits.

It might be a band-notch filter intended to keep you from watching certain pay-TV channels you aren't paying for (not all that likely as this would be *very* old technology these days).

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54 MHZ is the forward channel. The 24 MHz in between is needed to prevent equalization problems, due to the bandsplit filters.

Methinks it is to reduce interference to the TV that is generated by the cable modem. That cable modem generates a lot of hash, and interferes with cell phones up to at least 5 feet.

The use of the filter depends on what type of service you're getting. What combination of cable data, cable TV, MoCA, and/or cable telephony are you getting from Comcast?

It means quite a bit. Descriptions are nice, but (accurate) numbers are more important.

An SNBR-5/136 is a band reject filter that drops everything from 5 to

136Mhz, which makes little sense. The model should be something like SNBR-45/550. Please check your numbers. Also, what color is the stripe? Such a filter is what is normally used for cable data only connections where the uplink channels are above about 550Mhz and the return channel is below 30MHz. It's purpose it to prevent you from getting free analog cable TV service if you only subscribe to cable modem or telephony service.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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You misread my post, Jeff. It's SNB6-5/136. not SNBR-5/136. But it might be too old a code to find any documentation on it now. I think the Comcast technician installed it about 15 years ago. There is no color code on it, BTW. It's all mice stainless steel shiny. It is also not a cylindrical shape as your picture shows, but hexagonal. Otherwise it's similar dimensions.

I only have a ClearQAM HD TV (doing double duty as a PC monitor) and the Motorola cable modem operating from that splitter. The TV is connected through an STB that only provided SD picture but I can bypass it to get the local HD signals of the local stations. They all are powered from the same power circuit via power strip.

I also have an old analog set in another room that gets the TV signal through a Comcast DTA since Comcast dropped all analog signals in my area and encrypts everything except the local HD broadcasts. I do get good reception on both TV sets and good data speeds as well from the modem, despite the real old RG-59 cabling. Even with the coax filter removed. I get no telephony or other Xfinity services besides the broadband and Digital Economy TV package.

Yep. That's why I suggested you verify the part number. An SNB6-5/136 is very close to a PPC part number, but is not on the PPC web pile. Also a 5-136MHz band pass or reject filter makes no sense.

Also, could I trouble you to answer my question and disclose which services you're getting from Comcast? I can then guess(tm) which filter might be appropriate.

I have some old MHZ CATV catalogs from that era that might have something. I'll dig tomorrow. However, as I vaguely recall, all the customer premesis filters were cylinderical to make them difficult to remove without a special tool. The hard line connectors for the amps, couplers, and splitters were all hexagonal, to make them easy to install. I don't recall any filters inside hex packages. See for yourself:

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Hex shape suggests an attenuator, not a filter.

What shit brand of cable modem are you referring to?

The modern Motorola units don't do that. and they fire off at over

30Mb/s.

And the TV (band) is inside coax and won't get anything injected into it, unless you (or your installer) are an idiot at cutting a proper fitting as well.

The digital (read Internet service side) segment is yet another set of cable channels and the digital broadband 'service' is contained within standard 6MHz channel slots.

So, the whole thing is packaged within the standard cable TV channel slot on the digital side.

I thought the filter was for the cable modem, not 'for the TV side' as it were. On our system, it is a specific channel notch filter, which is what the numbering is about. It is no different than the "channel traps" they used to use to deny a customer a certain channel. If they bought that channel's subscription, they would come remove the "trap" from your taps out on the pole. That is a channel TRAP filter, which passes all channels except for the trapped channel.

This is a channel PASS filter that filters all channels except for the digital one, and that branch feeds our cable modem segment.

In your case, since it is on the cable TV feeder side, I suspect that it too is a channel TRAP filter (a narrow notch filter), which traps the channel the digital side is on and passes the rest.

I know even the TV stuff is digital now. I am using the term to refer to Internet service in this post.

It is a specifically set device to 'attenuate' a specific channel or band of channels. IOW, a notch filter.

I doubt the feed is so hot they need to cap the leg feeding the TV band. But it does appear to be only a 6dB pinch. But that is a guess... as well.

Mi modem is Motorola's SB6121 that I bought myself.

That's what I expected, too.

That's how it was here, too, except it was the cable box on the street as we don't have poles in my street.

Well, Comcast here now enforces channel subscription remotely by sending signals to their STBs and DTAs. Only the local stations can still be received with digital TV sets till they encrypt those, too.

You skipped that part in my last post, I'm afraid. I described the services in detail.

OK, a picture is worth a thousand words, I guess. So here are two pics of my filter in question: