Does Cable Affect Upstream?

All summer, I've been planning to split the output of my antenna to the rest of the house. It's been going directly to the main TV receiver for years. Anyway, the rest of the house is wired with 20 yr old cable. If I attach some crappy cable downstream of the splitter, will it affect the signal strength of the good cable upstream?

Yes, but it depends on how you set up your distribution system. Right now, the main tv has a straight shot from the antenna. Adding a splitter (one output to main tv and other to rest of house) will decrease the signal at the main tv by 3.5 dB. TV's further downstream will receive even less signal (3.5 dB loss from first split + cable run loss + losses from additional splitters). The main tv is only affected by the first splitter. Tv's downstream may drop below the digital cliff (ie no signal) if losses are too great from old cable, too many splitters, etc.

HTH,

Rick

The only possible quibble I might have is in assuming old and crappy just because its old. Coax is far more likely to degrade when its exposed to the elements outdoors, something indoors may last almost infinitely.

The point being, you can look for coax grade like rg-6 or rg-59 on the outside jacket, you can also use various means to test your coax, and even if you have some runs of lower quality rg-59, an amplifier of the pre-amp or distribution variety may make up for the losses.

Think about the signal coming from your antenna like a big truck.

If you own a big pick up truck and you have nobody inside of it and nothing in the bed, it will go as fast as it can go as quickly as it can go.

When you add a splitter, it is like putting a 1/2 a ton of junk in the bed.

When you add another 100 feet of wire, it is like attaching a 8,000 lbs. trailer to the back bumper.

Sooner or later, the drag from the additional wire will cause you to loose fringe reception.

When you figure out the efficiency of the system, you add together all the loss. The loss from the wire coming from the antenna to the splitter, the loss at the splitter and the loss of all the wire going out of the splitter to the other televisions.

The common question is - if I attach more than one television, will I loose some of the signal, and the answer is YES!

The next most common thought is that the tuner drags down the signal, so if I turn off the other televisions, will it give me more signal to the one television that I am trying to watch? and the answer to that question is NO! \ The tuner uses such a small portion of the signal present in the wire that it does not matter if you have 3 televisions going at the same time, or only one - the system still has the same amount of loss.

The question then becomes, if my wire is old and crappy, how much loss will I have. If you know the loss per a foot of wire at X frequency, you can figure out how much loss the wire has and you can figure out your power management. If the signal loss is too great, then you must remove the old wire and start all over again, or you will loose some of your most fringe signals.

A distribution amplifier will compensate for the loss in the wire of the system, but will not amplify a signal that is not present. At the same time, if you have a pre amplifier going from the antenna to the distribution amplifier, you know that there is a certain amount of noise created by the pre amplifier.

When determining the amount of gain, you have to subtract it from the noise factor and when you add a second amplifier, you then amplify the good with the bad and so you make the noise louder.

Sooner or later you hit the signal noise floor where the noise is stronger than the signal and all you have is Gaussian white noise or static. With a digital signal, you can loose 70% of the signal and still have a good signal, as opposed to a analog signal.

With the analog signal - when the performance of the signal was degraded, you had a poor picture and static in the sound. It was still watchable, but not perfect.

With the digital - it is all or nothing. Either you have a picture perfect signal and no interference, or you have nothing at all. The tuner act's just like your computer or your CD player. If you have a brand new CD, and there is no scratches in the CD, the music will play with no problem.

Drop the CD on the floor of your car a couple of times and wipe it off on your shirt and scratch the heck out of it, and pretty soon the music hops around and refuses to play.

The corruption of data is what causes the music not to play. When the CD player cannot find the data that is supposed to be on the disc, it looks at what is on the disc and then it tries to guess what the missing portion of the data is. If you have 4 zero's in a row, it's guess will be that the missing data is a zero. If you have 3 - ones in a row, it's guess will be that you have a one.

The problem with that is that there is millions of ones and zero's flying through the air at any one time and it is so hard for your receiver to guess what it might be that it mostly just locks up and you get no sound or no video until a good signal returns.

So my advice to you is to replace all the old wiring in the house with new wiring of a known value - good wire and then you will minimize your problems in the long run.

The problem with Quad Shield wire is that your signal travels at about the speed of light when it is transmitted and when it hits the Quad Shield wire, it is constricted more than with regular RG 6 wire and so the wire slows down the signal.

It is not a problem right now, but 30 years from now, the technology might get so fast that it will cause a problem with data transfer.

Thanks, Everybody.

I realize that adding a splitter will reduce power everywhere downstream. I was wondering about the wiring on each side affecting each other. I was sleepy last night when I posted, so let me try to be more clear.

Say I have 100 ft of wire going to TV1 now. Power at TV1 would be antenna power - 100 ft of cable loss. (leaving out amp and tuner losses for the sake of clarity)

If I split right at the antenna and attach another 100 ft of cable going to TV2, which would be correct?
TV1 power = antenna power - splitter loss - 100 ft of cable loss?
or
TV1 power = antenna power - splitter loss - 200 ft of cable loss?

I think you're telling me it will be the first one, right?

Say I have 100 ft of wire going to TV1 now. Power at TV1 would be antenna power - 100 ft of cable loss. (leaving out amp and tuner losses for the sake of clarity)

If I split right at the antenna and attach another 100 ft of cable going to TV2, which would be correct?
TV1 power = antenna power - splitter loss - 100 ft of cable loss?

Yes this is correct.
While without amplification the old cable may well make it difficult or impossible to get a strong enough signal on the TV(s) that it is serving it shouldn't effect the TV upstream from it.

While older cable, such as RG-59, may have a higher SWR causing more reflected signal, this power is relatively low to begin with, and will be down a minimum of another -7dB (may be way more, I'm not aware of the isolation specs on splitters) relative to the incident signal at the 1st TV, so it shouldn't be an issue.

And I thought your original question was stated quite clearly.:)

Yes this is correct.
While without amplification the old cable may well make it difficult or impossible to get a strong enough signal on the TV(s) that it is serving it shouldn't effect the TV upstream from it.

While older cable, such as RG-59, may have a higher SWR causing more reflected signal, this power is relatively low to begin with, and will be down a minimum of another -7dB (may be way more, I'm not aware of the isolation specs on splitters) relative to the incident signal at the 1st TV, so it shouldn't be an issue.

And I thought your original question was stated quite clearly.:)And you answered without a 3000 word diatribe on digital broadcasting!