Semi-OT: Splitting a coax cable signal without losses?

[Ethan]

Is there a way to distribute/split a signal (specifically my home's TV cable & cable internet) from a 75ohm coaxial line without losses? The people that wired this house up used a bunch of splitters that result in a 3.5dB loss for each time the signal is split. Resulting in picture being less than great and modem signal strength compromised.

Help?

 

[gyraf]

You can get these small amplifiers that are made for exactly that purpose....

Jakob E.

 

[Ethan]

Could you point me to an example or supplier? What are they called?
Thanks!

 

[Scodiddly]

Markertek, of course, and you're looking for a "distribution amplifier". Or Radio Shack might still carry that sort of stuff...

 

[Ethan]

Ah!
Thanks!

 

[aurt]

A distribution amp will work fine for the cable signal, but I'd bet it's not designed for two-way traffic, and might be useless for the internet. You should be able to put your cable modem right up front and do any home networking either on ethernet or wifi, and then split with DAs to your hearts content for the TVs.

 

[PRR]

> a bunch of splitters that result in a 3.5dB loss for each time the signal is split.

There is no free lunch. Pretend the cable company gave you a 1 Watt signal. You passively split it to two loads. The most power each load could get is 1/2 Watt. What is the ratio of 1W to 1/2W? 3dB. Your splitters are within 0.5dB of perfection. (In audio, such gizmos give 1dB or 2dB excess loss.)

Cable TV signals are usually pretty robust, and a few splitters should not be a big deal. Note that the cable company may not allow splitters! They like to charge for every TV set, and then they supply the splitters and divert enough line-signal into the house to pass all the splitters.

Weed out excess splitters. A 4-way splitter has 7dB loss, and two levels of 4-way split give 16 outputs at 14dB loss. This may or may not be tolerable. Certainly better than a chain of 15 2-way splitters, where the last TV gets 52dB loss!

Or stuff an amplifier in there. But still, go through your splitter-maze, weed out excess splits, and try to equalize the loss to each TV. Count the splitters from each TV back to home plate, sum the rated losses. If the losses are not all similar, then some TVs will overload while others are still weak.

> modem signal strength compromised.

Modem should be as close to the street (as the wire runs) as possible. Mine is in the basement next to the service entrance. It is DSL, and it taps right on the telco-box, all the talk-phones come after the DSL split/filter. (I could NOT get a good DSL signal in this haywire house any other way.) Cable-modem, same thing, except near the cable entrance. Once you get to EtherNet, you can run data ALL over the house with insignificant loss.

 

[Kev]

Even though this is an RF sort of coax thing I'd just like to tell all
... that I have a simple PCB that uses a MAX chip (I think) to give 1 in 4 out. 75 ohm video stuff.
There is so much DIY that I just don't have time to tell you about. :sad:
Some times a T piece can get the result you want BUT double termination of video can be very obvious.

 

[NewYorkDave]

CATV distribution is a hornet's nest of compromises. Believe it or not, there are times when passive splitters are preferable to amplifiers. Amplifiers add noise; if you can split passively and still get, say, 0 to 10 dBmV at each receiver, then you're probably better off with the splitters (as long as they're good splitters with adequate bandwidth. Old splitters, which may have been used in your house, are useless above 300MHz or so).

I should point out that a CATV "distribution amplifier" system is usually a one-in, one-out amplifier followed by a bunch of splitters or directional couplers. One thing many DIYers don't know is that it's generally a good practice to terminate unused splitter outputs.

Cable modem is tricky because it uses the sub-band (below channel 2) that many splitters won't pass very well. I agree with previous statements that you should locate your tap-off for your modem as far upstream as possible.

Before you do anything, ask your cable company if they would move your "drop" to a higher-output tap on the directional couplers that feed your neighborhood. It would be better to get a stronger signal on your drop, strong enough to allow you to split passively, than to take a weaker signal and amplify it and then split.

Also, check the coax in your house. Older types of coax and connectors are lossy/leaky compared to modern types. If you find any of that old skinny RG-59 junk and two-piece F connectors, replace them with good RG-6 and snap 'n seal F-connectors. It can make a difference.

I won't even get into setting "tilt" right now, since presumably the cable runs in your house are not very long. But you should pay attention to the amount of tilt on the signal coming in on your drop. Is the reception worst on the lowest channels, gradually improving as you go up the dial?

Hey PRR, you're off dialup now? Congrats! The day I ditched dialup for DSL was a happy day indeed.

Kev, there's an Analog Devices chip that makes a nifty video DA of up to 8 outputs. I was inspired to check it out when I noticed that it's used as the output stage in the new Leitch DAs we used in our truck and MCR. I got a couple of free samples from AD a while back--I'll check on the part # when I'm at work tomorrow.

 

[adrianh]

The CATV type of amps
handle a lot of signal before they overload.
You are going to need to spend money to get a good amp.

Markertek part #'s
Try, MUVB-35
PM-CA-1M

This one looks like it may be the ticket CVT-PIA
The above one may work with a modem!

 

[casuarina]

How about use two stages of 74VHCU04 as fan out? I don't know if this will have serious sync problem caused by the delay of 74VHCU04 logic IC.