Multiple tvs on one antenna
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Multiple tvs on one antenna


This is a discussion on Multiple tvs on one antenna within the DTV | HDTV Reception and Antenna Discussion forums, part of the Over-the-Air (Antenna TV) category.


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  1. #1
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    Multiple tvs on one antenna

    How do I run multiple TVs on a single antenna? I've got a roof top with one single coax run to my family room TV. It's an old house, but I think I can manage to run some more coax into the other 2 rooms we'd like to connect to the antenna. Can I just use something like a 3 way splitter from the antenna or do I need anything else?

  2. #2
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    Quote Originally Posted by GinoS View Post
    How do I run multiple TVs on a single antenna? I've got a roof top with one single coax run to my family room TV. It's an old house, but I think I can manage to run some more coax into the other 2 rooms we'd like to connect to the antenna. Can I just use something like a 3 way splitter from the antenna or do I need anything else?
    I'm wondering if, when using a splitter, you'd need an amplifier because splitting the signal like that would weaken it to each television.

  3. #3
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    Multiple tvs on one antenna

    I have a number of TVs on a single antenna and I added something like thos:

    Walmart.com: Philips 24dB Two-Output Video Signal Amplifier, PH61111: TVs

  4. #4
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    Splitting the signal three ways will cause about 7 db of loss and that's a lot. Add a cheap 10 or 12 db distribution amp before the 3-way splitter and the picture on all three tv's will look as good, if not better than ever.
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    Quote Originally Posted by Tim58hsv View Post
    Splitting the signal three ways will cause about 7 db of loss and that's a lot. Add a cheap 10 or 12 db distribution amp before the 3-way splitter and the picture on all three tv's will look as good, if not better than ever.
    Maybe that's why I'm getting a lower signal strength using the antenna on the rooftop of my building versus the rabbit ears. I don't think my landlord put an amplifier anywhere. It still works though, picture looks fine, just a lower strength on the meter.

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    Quote Originally Posted by NYCLA* View Post
    Maybe that's why I'm getting a lower signal strength using the antenna on the rooftop of my building versus the rabbit ears. I don't think my landlord put an amplifier anywhere. It still works though, picture looks fine, just a lower strength on the meter.
    That could well be.

    You could try adding a distibution amp which may increase the signal strength, but generaly you have to add the amp before the cable is split.

    Of course if you're splitting that signal to more than one tv, the distribution amp will help.

    Years ago I added a VHF/CATV amp to our one tv set (pay tv) and would swear that it made the reception better.
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  7. #7
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    Quote Originally Posted by GinoS View Post
    Can I just use something like a 3 way splitter from the antenna or do I need anything else?
    If the signals are strong enough where you live, you may not need any amplification at all -- just the splitter. That's worth a try first; add a amp only after reception becomes less than reliable on one or more sets. If you need a distribution amp, stick to low-noise models made by Winegard or Channel Master.

    There are a couple of additional considerations in a three-way split:

    • Three-way splitters aren't as widely available as two- and four-way splitters. If you can't find a three-way, get a four-way. Be sure to cap off the unused connector with a coax terminator to prevent signal reflections and "leak," either one of which will degrade reception very noticeably. Terminators cost about a buck apiece.

    • Most three-way splitters are "unbalanced" -- in other words, the built-in signal loss on one connector is significantly greater than it is on the other two ports. Most commonly, it's -4 dB, -4 dB and -7 dB. With this type of splitter, connect the shortest coax run to the -7 dB port and the longer runs to the other two.

  8. #8
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    I know this is redundant, but as Don points out, just try a splitter first. Way so many people run out and add a "cheap" amp only to find their reception is worse. Only add an amp if one or more sets looses a channel after splitting the signal.


    As Don points out, avoid at all costs buying a cheap distribution amp from walmart.

    Notice the spec of the amp at 4 db noise figure. Here the larger the db the worse the reception. It runs $24 plus your local tax and shipping.

    Plus, if you need an amp, more than likely your signals will be much better the closer you get the amp to the antenna, if possible right at the antenna on the mast.

    An "inexpensive" but not cheap amp. For $40 shipped to your door, you can pick up Winegard HDP 269 SquareShooter Pre-Amplifier for SquareShooter SS-1000 (HDP-269) | HDP-269 [Winegard]. This amp you can if possible for you mount up on the antenna mast so the amplifier over comes the loss in your entire system if placed at the antenna mast. If not it's still a better amp.
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    I don't get why you need a low noise distribution amp. You would only use a distribution amp because you aleady have a good signal and just want to maintain that signal strength through long cable runs and or splitters. It's not like you're using it to amplify weak signals so what's the harm?

    Yeah, there's the cheap models like I've used, the Walmart, Radio Shack, etc. kind which have worked fine for me. Or one could spend maybe twice as much and get a Winegard or Channel Master low noise distribution amp which in theory should work better. Or you could spend five or ten times as much on a top O' the line Blonder Tongue distribution amp which has high noise figures ranging between 4.5 and 7 db just like the cheap ones.

    I myself own a Blonder Tongue MVB-62 distribution amp and it's noise figures are 5.4 on low vhf/fm and 6.2 on high vhf. With a gain of 55 db, it'll smoke anything Winegard or Channel Master has, at least that I know of.

    Seems the cheap amps and the best amps have high noise figures but I'm not too big to admit if I'm wrong...so school me.
    Last edited by Tim58hsv; 09-02-2009 at 07:12 PM.
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  10. #10
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    Quote Originally Posted by NYCLA* View Post
    Maybe that's why I'm getting a lower signal strength using the antenna on the rooftop of my building versus the rabbit ears. I don't think my landlord put an amplifier anywhere. It still works though, picture looks fine, just a lower strength on the meter.
    Digital doesn't need a lot of signal strength. As long as it's strong enough to get a lock on the signal without dropouts, a stronger signal won't make the picture look any better. Now, if some of the channels start to freeze or go away at certain times of the day, you may need a bit of amplification. But amplifying it in your apt. will also amplify any noise or interference the building cable picks up, and may not help at all, or make it worse.

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    Quote Originally Posted by Tim58hsv View Post
    I don't get why you need a low noise distribution amp. You would only use a distribution amp because you aleady have a good signal and just want to maintain that signal strength through long cable runs and or splitters. It's not like you're using it to amplify weak signals so what's the harm?

    Seems the cheap amps and the best amps have high noise figures but I'm not too big to admit if I'm wrong...so school me.
    Seems I explain this once a month.

    The antenna receives a A db of signal. But also receives X of noise. This then gives you Y which is equal to A/X or signal to noise ratio of the signal.

    If you don't have an amp, then you loose L in the downlead and any splitters, etc getting to the TV.

    So the TV then has y-L of signal available.

    Here the signal goes into the receiver. In the receiver there are obviously RF circuits that process the signal.

    There is always thermal noise from the electricity passing through the electronic devices. that creates noise. This is why very low noise amps used in quantum physics are kept at very low temperatures. So not only is the amount of noise added a function of how the electronics are made, but their temperature. So if you know a little chemistry or physics this noise is actually movement of the electrons in the receiving device. Hence if it's hotter they move more and if there is more current they move more, then the factor of how the device is made plays a substance role.

    Most TV receivers and CECBs add about 5 to 8 db of noise right away to the signal to boil it down.

    So now at the TV we have for signal

    y-l-N where N is the noise in db added by the receiver.

    So to receive a signal, it has to be strong enough that after we loose some in the feed system , y, then it has to over come the noise, N it will decode. Remember also that Y contains noise.

    ====

    Now add an amp that is NOT in overload.

    The antenna still receives y db amount of signal, that doesn't change.

    It goes directly into the amp assuming a perfect connection to it (not in the real world but simplifies things).

    The amp adds noise to the signal since it is a electronic device just like the receiver explanation above. Lets call this noise, Namp.

    Here is where you must understand a little about RF reception that goes a little deeper.

    The antenna does receive y amount of signal. But actually it's y amount of signal above the ambient noise the antenna also receives. So it's not a simple amount but has to be thought of as an amount above another amount. So y is actually an expression of the Signal to Noise received by the antenna.

    This y goes into the amp. The amp amplifies both the signal and the noise. So despite the amp rated at a gain of G db, and the signal comes out stronger by G db, so does the noise, so y remains the same, remembering that y is really a ratio, not an independent value.

    The amp also adds Namp of noise. So in a sense it makes y worse by N as the signal is amplified. Here is the first part of why a lower noise amp is better. The lower the noise of the amp, the less noise is added. So no matter what any time you add an amp, y goes lower, because remembering again it's a ratio of signal to noise, the noise or denominator in the ratio grows.

    But all is not lost, as now there is more signal to get through the losses through the feed system that again includes any coax, or splitters, etc.

    So now with the amp, we have the y increased by G, but reduced by Namp. But G adds so much gain it over comes the loss in the feed system.

    note that the ratio y actually gets worse through the amp.

    The idea here as you stated that Gamp over comes the l or loss of the feed system, which hopefully it does.

    But now we have more signal from Gamp, but y is actually less because of the amp noise. It's the gain of the amp that overcomes the loss of the feed system.

    One can think of Y ratio riding on the extra gain of the amp.

    When the signal gets to the receiver we hope that the Gamp is more than the loss of the feed system, but not by too much.

    So lets pretend the loss of the feed system equals the gain of the amp.

    So at the receiver the Gamp minus the L loss of the system is then zero.

    So we have the y the antenna received intact at the receiver, but with the noise the amp added.

    So one would think, wow, why put in an amp? you increased the noise?

    Well there is more.

    Remember above I said the receiver had noise? And that noise figure of a receiver is 5 to 8 db. But since we put an amp in the system the front end of the receiver is actually the amp, it is just physically distant by the length of the feed line.

    A fact you must buy out right is the first stage of any receiver's noise figure sets the noise figure for the entire receiver.

    So without an amp we had Y-L over coming 5 to 8 db of noise.
    Now with an amp we have Y with 3 db noise added by the amp but since it's the first stage of the receiver now, the receiver lowers it's noise to the noise of the amp.

    So if the amp has noise of 3 db and the receiver 6 db, with the amp, we lower the noise figure of the entire system by 3db. The is the same as doubling the signal or doubling the size of the antenna.

    Now if you put the amp at the receiver and it has a lower noise then it lowers the noise of the receiver why amps into noisy receiver help right at the back of the receiver.

    BUT! when placed at the back of the receiver, the signal into them is weaker, but with the same amount of noise, so y is much lower. This is because not only does the feed system lower the signal but actually adds a little bit of noise itself, since it too is a circuit.

    Hence, the close to the antenna you place the amp, the better the signal to noise ratio exists to preserve. Also the lower the noise of the amp, the lower the noise of the system (the system being the antenna, amp, feedline, and receiver.)

    There may be some redundant information here, spelling errors, but this was written as a draft.
    The more I understand, the less I know.

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  12. #12
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    Other potential problems with amps

    If you have any VHF channels, adding an amp may also increase the chances of impulse noise dropouts due to electrical interference from appliances, computers, motors & light switches. And adding an amp without an FM trap may increase interference to VHF chs from nearby FM radio stations.

  13. #13
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    Quote Originally Posted by Piggie View Post
    There may be some redundant information here, spelling errors, but this was written as a draft.
    Please don't apologize: This is the best explanation of the physics behind an amplified antenna system I've read anywhere -- geeky, perhaps , but clear and thorough.

 

 

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