[kwlug-disc] OT:Cable Splitters/Rogers

[Andrew Kohlsmith (mailing lists account)]

On Jun 9, 2014, at 12:42 PM, unsolicited <unsolicited at swiz.ca> wrote:
> New standard, like said, thicker, more insulation. I first remember seeing it when satellite service started coming out.

Basically RG59 is specified to have a defined frequency response/signal loss characteristic. As long as the cable meets the spec it can be called RG59.

RG6 has a more demanding spec (frequency response and loss characteristics are defined for a larger range of frequencies). To meet that, the dielectric had to be made bigger, which is why the cable’s bigger.

Old analog cable TV only had to go to (I think) 50MHz or so (this seems ridiculously low to me but my quick googling isn’t proving that wrong). Digital cable uses much more of the frequency spectrum so much better cabling(RG6) becomes important. Satellites were the first guys to really need this kind of bandwidth which is why you found it there first.

At higher frequencies, RG6’s loss is *considerably* lower than RG59’s, but interestingly it has *worse* loss characteristics at low frequencies than RG59. Channels which occupy the higher frequencies will be crappier on a chunk of RG59 than they will be on a similar chunk of RG6. Bad crimps, kinked wires, loose/corroded connections all play their part as well. Just because a cable or connection looks good doesn’t mean it’s good across frequency, which is a tricky concept for a lot of people to understand. 

You’re absolutely right: digital signal loss results in pixelation/blockiness, especially in fast-moving or quick-changing scenes. Audio can start to stutter as well. Analog signal loss is more “smooth” — you get fuzz/snowy scenes and general degradation. Ghosting is almost always the result of poor or missing termination, causing the signal to bounce off the unterminated port and arrive at your TV slightly later (think echo, it’s the exact same thing). Bad/missing termination on digital systems looks exactly like digital signal loss: blocking/stuttering/etc.. A quick check is to look at all the splitters in the house and make sure that any unconnected ports are terminated. Terminators look like regular connectors with no wires coming out of them: http://www.cp-electronics.com/image_lg/PVFT1.jpg. Every unconnected splitter port should have one, but the better solution is to use splitters with fewer ports/reduce the number of splitters altogether.

I only had about 15 feet of coax between the outside demarc and my cable modem. Replacing that with a decent quality RG6 with waterproof connectors and making sure there were no tight bends or strain on the wire gave me 4dB of additional margin on my cable signal across all frequencies it was interested in. YMMV of course, but it’s worth taking a good look at everything. Every connection, no matter how solid, eats into your margin. A good (if conservative) rule of thumb is to assume a 1dB or so loss for every “break” in the cable. Splitters usually list how much loss they have at each port, and add another 1dB for the actual connection itself.

It doesn’t sound like much, but remember that 3dB is a halving of the original signal level. When Khalid mentioned that newer boxes are very sensitive he means that they’re able to lock on and recover signals that’ve been attenuated to hell through poor cable plant, lots of connectors/splitters/staples/etc.. Receiver sensitivity is a very important metric in my opinion. Same with noise figure (NF) when it comes to amplifiers. A lot of people get into ATSC and buy the cheapest, strongest “low noise” amplifier they can find, thinking that the 40dB gain it gives will help, but forget to look at the NF and don’t realize that their strong amp is adding a good 5dB of noise to the signal they’re trying to pick up. (/aside)

Another aside: A friend just had a new Rogers install. The guy must have used Thor’s staple gun; ALL of his brand new cable was squished to almost half its diameter at every staple. So much for Rogers expert installers!

-A.