[kwlug-disc] OT:Cable Splitters/Rogers

[Bob Jonkman]

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Andrew Kohlsmith wrote:
> Splitters usually list how much loss they have at each port

And if the splitter has three outputs then one of them is likely has a
3dB loss, and the other two have a 7 dB loss (because the first is one
fork off a Y split, and the other two are a second Y split off the
second fork of the first Y split).  So make sure you're connected to the
output with the least loss.

But better to get a barrel connector and a short extension.  I hear
Computer Recycling sometimes has parts like these :)

- --Bob, who wonders why the losses on the second outputs aren't
additive for 6dB loss each...


On 09/06/14 01:17 PM, Andrew Kohlsmith (mailing lists account) wrote:
> 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.
> 
> 
> 
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