General Question

robmandu's avatar

Can any coax two-way splitter also be used to combine two sources to one line?

Asked by robmandu (21215 points ) January 12th, 2009

I have a splitter that looks similar to this guy. But the Radio Shack page lists theirs as a hybrid capable of working in either direction: as a splitter or as a combiner.

So, I already have a generic-looking one lying around. And I have two coax sources (satellite and over-the-air antenna). But only one coax input on my TV.

I’d like to plug both my sources into the two port end of my generic splitter and my TV to the one port end.

And my hope would be that I could toggle between the two sources on my TV just by selecting either CATV or AIR as the source.

Is my generic splitter okay? Or should I try to get this Radio Shack hybrid model?

Yes, I know about A-B switches. But that’s not on the table for this discussion.

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23 Answers

AstroChuck's avatar

I’m confused. Does your generic splitter have some kind of A-B switch? If no, I don’t see how it would work.

robmandu's avatar

First off, the hybrid model on the Radio Shack site is adverted to do exactly what I want to do. So, in theory, my idea should work.

No, the thing itself is not a switch. In general use as a splitter, you can plug, for example, two televisions into one coax jack from the wall. One source split to two targets.

I want to do the reverse. I have two sources that I want combined onto the same line for one target.

I just wonder if that particular model is special… or can any old two-way splitter work in reverse, too?

fireside's avatar

I would say that toggling your TV wouldn’t do anything because the input will be from the same source.

Some older splitters may not be able to handle two signals coming in at once, but you should definitely give it a try with the one you have. Most likely, you just have to have one or the other off to view the source from the one you want to watch.

robmandu's avatar

@fireside… sorry wrong.

To be clear, I’m not talking about “inputs” like HDMI, A/V, Component, Composite, etc.

Remember folks, your tv must be told what the incoming video source actually is when using coax. Either antenna or something like cable (or satellite). In “antenna” mode, you get 2–13 VHF channels plus the UHF range. But in “catv” mode, it supports up to 125 (or whatever) channels.

My tv has a single coax input. It can either be connected to catv or to an antenna. And indeed, I have done both. Depending on which is connected, I use the “catv/air” toggle switch on my remote.

For right now, I must unplug the antenna in order to plug in the catv source. But if I get this splitter/combiner thing on the line, I shouldn’t have to jack with the cables no more.

Makes sense?

fireside's avatar

Yeah, I thought better of it as soon as I posted, but you were already typing.

I haven’t used an antenna in so long. But I would still try it with the one you have first. If the signal comes through unclear, then there is probably some crossing of the signals and you may want to go to Radio Shack.

robmandu's avatar

Yah, I’m a big fan of “just trying it.”

OTOH, even though the antenna source isn’t powered in any way and the additional signal load on the line shouldn’t be too much for the tv in any case, I thought I’d ask first.

I’ve been burned too many times thinking, “Oh yah, this should be just fine. What could possibly go wrong?” ツ

fireside's avatar

lol, well there is nothing in that setup that will fry or damage anything. It will most likely work just fine.

worst case scenario, you get the tv pulled out from the wall get the old one setup and then get a bad signal. Do that during the day and you can always get up and go right to Radio Shack before you push the tv back to the wall.

robmandu's avatar

< < glad he’s talking about a ~35lb. LCD on a stand… not a 120+lb. CRT in a cabinet.

fireside's avatar

lol, mine’s still a beast
but at least the cabinet has wheels

IchtheosaurusRex's avatar

Not by themselves. They typically mate a low-impedance output to two or more high-impedance inputs. Mixing low impedance outputs together without buffering of some kind leads to crosstalk and can damage the output drivers of one or both of the units under some circumstances. At a minimum, you need to use a resistor on one of the sources. I don’t know how the Radio Hack splitter/combiner works, but I suspect that’s what it does. If so, the signal will be attenuated, but probably not enough to notice.

robmandu's avatar

Oh ho!

I was wondering why there was a “box” involved. Additional passive electrical components would explain it. And preventing damage is a good thing.

critter1982's avatar

Likely the one you have is not a capable of combining two signals on a single line. Most generic splitters do just that, they run 2 lines in parallel splitting the signal between both which in general gives you a less than perfect picture, although if you are using coax directly into your TV the picture is going to be less than perfect anyways. The one from Radio Shack uses a circuit board (likely?) to convert both signals into one in which your television can read as either signal 1 or signal 2. If you use your splitter to combine these signals likely what you’ll get is a bunch of interferences and you’ll probably just get a bunch of snow on your TV or lots of lines. It won’t hurt to try it out though. There isn’t enough current running through to damage anything in your TV.

robmandu's avatar

Got the Radio Shack hybrid splitter.

Works okay… and like @IchtheosaurusRex said, there is some attenuation of signal from both sources. But it’s workable enough for now.

Thanks!

sndfreQ's avatar

Sorry getting late to this Q…the issue with crosstalk and impedance mismatching (combining) would seem to be the real issue with the receiving end, as the signals combined result in a different “summed” signal than what you’d get from a true switch/splitter. I’d probably steer clear of this combination, though I don’t think it would pose any real threat to the sources’ electrical outputs (other than introducing RFI into the chain.

robmandu's avatar

Yah, I can see where having a true a-b switch would work best. It’s definitely noticeable having both sources “in-line”, even with the hybrid combiner.

pschimpf's avatar

Robmandu. Interesting. I found this because I had exactly the same question. My suspicion is that the splitter product has just been relabelled for modern times. Used to be that people just needed to split their VHF antenna to multiple sources. Now some people are finding that they need to combine separate VHF and UHF antennas for over-the-air digital broadcasts (like me). My hope is that the device uses transformer coupling. Did you ever try your old device? I’ll be trying that one first as soon as I can get my kid away from Sponge Bob. :-)

robmandu's avatar

No, didn’t try the plain old splitter.

Matter of fact, in the months since trying this, I’ve pretty much given up on it. I think a true a-b switch would be the way to go… but they’re pretty pricey.

Trying to combine the two signals (one from HD antenna, one from the standard-def DVR) is frustrating:

- the DVR signal shows noticeable snow, artifacts
– the HD signal is degraded to the point that some channels are slow to appear and others cannot be auto-detected by the TV’s tuner.

So… I gave up on the splitter/combiner and would just unplug one cable, then plug in the other, then change the Input source on the TV… and then realize I’d forgotten what I was going to all the trouble for… and then just leave to do something else.

pschimpf's avatar

I just tried both. Both worked for me, but the old-fashioned splitter worked better. Maybe because it didn’t claim to have “DC pass through” (IOW, a wire) between one side and the other. My application is different than yours though – I’m simply combining an old VHF antenna with a new (home-made) UHF antenna in order to improve reception on over the air channels that have migrated out of the VHF band in the digital switchover. I’m a bit confused by your application. Most DVRs have an antenna pass-through. Plug your antenna in on the input side and the output (SVideo, HDMI, or coax) goes to your TV. Turn the DVR off and you get the antenna signal. Turn the DVR on and you get the DVR signal. Actually, my DVR works a little differently, but I won’t bore you with that. If you’re getting your DVR signal on coax, then it is probably putting a signal out on ch3? Yeah, you don’t want to try to combine that with a low-power antenna signal. But you shouldn’t have to. You should be able to just turn the DVR off (or tell it not to play) in order to have it pass your antenna signal through. Maybe you’re not doing that because you have a Sat box on the input side of the DVR? If so, then plug your antenna to the antenna input of the Sat box. Then you have to turn the Sat off in order to get the antenna signal to your DVR (and subsequently, to your TV).

robmandu's avatar

My DVR always puts out a signal (to the 2nd TV), even when it’s off. The signal is a info graphic telling you how to turn the DVR on, what you have recorded, what’s coming up, whatever… acts like a screen saver.

That’s why I always get interference for the antenna. :-\

Marianna's avatar

I have no answer, just a question. I have an old TV and a new HD converter. I am 81 years old and need concise instructions on how to hook up my VCR, DVD to work. I have hooked things up and get pictures on my TV from the DVD, but not from the VCR. Also I would like to tape on the VCR . The stupid converter box only stays on about four hours. I have called local Radioshack stores here and they don’t know any more than I do!

IchtheosaurusRex's avatar

@Marianna , I believe your best setup is to connect your HD converter box to your VCR, then connect your VCR to your TV set by way of the coaxial antenna connectors. You would hook up your DVD player to the red, white, and yellow RCA plugs on the TV, if it has them. You would play your VCR and watch TV through channel 3 on your TV set. You would watch your DVD player using the TV/Video switch. Other configurations are possible, especially if your VCR has more than one set of line-in connectors. If it does, you often find them on the front of the unit. Also, if your TV has more than one set of line-in connectors, you can use them, too.

I know this is complicated and pictures would help. If you know the make and model of your TV and VCR, I could look it up for you and see if I can help you out further.

gavgto's avatar

no you have to buy two diplexers for it to work correctly not a splitter!

gavgto's avatar

a splitter won’t work correctly only 2 diplexers which look exactly the same as a splitter will work that u can pick up at radio shack for cheap… the difference is a diplexer allows current to flow thru one side of the wire while the other side will work with any over tha air or cable broadcast so you can receive both your stellite and cable signals on one line! email me if u have aby questions!

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