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Guest Message by DevFuse

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OTA antenna signal spliter?


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27 replies to this topic

#1 OFFLINE   hobie346

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Posted 10 May 2009 - 04:34 PM

Any suggestions for an OTA antenna signal spliter? I did a search on SolidSignal but nothing useful.

TIA.

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#2 OFFLINE   jdspencer

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Posted 10 May 2009 - 05:01 PM

There's nothing special about an OTA splitter. You can probably get one at Radio Shack.
DirecTV since '96, Waivers for ABC, CBS, NBC, & Fox, HR23-700 & HR24-500/AM21, using ethernet based MRV.

#3 OFFLINE   Grentz

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Posted 10 May 2009 - 05:12 PM

Solid Signal has plenty of them, they have an entire section in fact:
http://www.solidsign...ignal Splitters

Personally I have had good luck with Eagle Aspen, Skywalker, and Perfect Vision. OTA does not need anything over 1000MHZ, but if you get one with a higher rating it will work fine.
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#4 OFFLINE   robq391

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Posted 10 May 2009 - 05:35 PM

Just make sure that if you're going to amplify your OTA signal that you do so as close to the antenna as possible & definately before you split it.

#5 OFFLINE   hobie346

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Posted 10 May 2009 - 05:40 PM

There's nothing special about an OTA splitter. You can probably get one at Radio Shack.


That's what I thought until I bought one from the local RS and then lost channel 12 (DTV 11.1).

#6 OFFLINE   hobie346

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Posted 10 May 2009 - 05:43 PM

Solid Signal has plenty of them, they have an entire section in fact:
http://www.solidsign...ignal Splitters

Personally I have had good luck with Eagle Aspen, Sky walker, and Perfect Vision. OAT does not need anything over MHZ, but if you get one with a higher rating it will work fine.


Thanks, I don't know why the search I did didn't show anything.

I bought a MHz to 1GHz one from the local RS but lost channel 12 (DTV 11.1) afterward. The current one shows a -4dB signal lost on both outputs.

Edited by hobie346, 11 May 2009 - 07:42 AM.


#7 OFFLINE   Grentz

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Posted 10 May 2009 - 06:39 PM

If your channel 12 is very weak a splitter could make you lose it. All splitters will have some loss, some are just slightly better than others.
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#8 OFFLINE   jdspencer

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Posted 10 May 2009 - 07:26 PM

You probably need to put a preamp on the antenna.
DirecTV since '96, Waivers for ABC, CBS, NBC, & Fox, HR23-700 & HR24-500/AM21, using ethernet based MRV.

#9 OFFLINE   carl6

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Posted 10 May 2009 - 08:02 PM

All splitters will have some loss, ...


Right at 3db per split, or about 1/2 the original signal out of each branch for a 2-way split.

#10 OFFLINE   texasbrit

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Posted 10 May 2009 - 08:38 PM

Thanks, I don't know why the search I did didn't show anything.

I bought a MHz to Hz one from the local RS but lost channel 12 (TV 11.1) afterward. The current one shows a -4dB signal lost on both outputs.

3.5 to 4db is typical for a splitter. Remember if you split a signal two ways you have to lose at least 3db, because 3db means half the signal. You can't have a two-way splitter with a loss of less than 3db, it's just the physics.

#11 OFFLINE   CCarncross

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Posted 10 May 2009 - 09:43 PM

If you have any weak stations, you probably want to go with an amplified splitter.

http://www.solidsign...&CAT=Amplifiers

#12 OFFLINE   hobie346

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Posted 11 May 2009 - 07:40 AM

I quess I'll need to add some type of amp to my OTA signal. The question is which the right way to do it? What's better, a pre-amp and seperate splitter or a dist amp? Where does the power get inserted?

I'm looking at at least one 30' run from the antenna to the spliter and two runs of 20' from the spliter to the receivers.

#13 OFFLINE   jdspencer

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Posted 12 May 2009 - 08:35 PM

I'd put a preamp at the antenna. A distribution amp will amplify whatever noise gets into the coax from the antenna. The power inserter is put before a splitter.
DirecTV since '96, Waivers for ABC, CBS, NBC, & Fox, HR23-700 & HR24-500/AM21, using ethernet based MRV.

#14 OFFLINE   Scott in FL

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Posted 12 May 2009 - 10:56 PM

Noise getting into coax isn't really a problem. The reason you put the amplifier as close as possible to the antenna, and always before a splitter, is because the signal is at its highest level as compared to the noise floor of the amplifier.

Some think that today's amplifiers are so quiet that this is not a problem, but even an ultra quiet preamp with a noise floor of say 2 dB will contribute a significant amount of noise to a weak signal at the end of a 30' coax run. The result is a degraded signal-to-noise ratio. So always put the amplifier at the antenna.

Distribution amplifiers typically have higher noise figures than preamps but can handle higher signal levels. A low noise preamp is a better choice at the antenna. But too much gain can cause problems, as can over driving the preamp if you live close to any TV or FM transmitters.

There's no simple answer. You want a low noise preamp with sufficient gain to overcome any losses after the preamp (from a long coax run or splitters), but without too much gain or sensitivity to overload.

#15 OFFLINE   hobie346

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Posted 13 May 2009 - 08:23 AM

Thanks Scott and JD for the help.

Any recommendations on a quality preamp?

#16 OFFLINE   Scott in FL

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Posted 13 May 2009 - 08:51 AM

The Channel Master CM7777 is a quality, low noise preamp that many on this forum have had good luck with. It's not cheap, but it's a good preamp. You can amplify UHF and VHF signals separately or combined, and it has an FM trap. I've always used preamps such as this in fringe or near fringe areas with excellent results. If you live close in to any transmitters, be careful. It has a lot of gain.

#17 OFFLINE   hobie346

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Posted 13 May 2009 - 12:02 PM

The Channel Master CM7777 is a quality, low noise preamp that many on this forum have had good luck with. It's not cheap, but it's a good preamp. You can amplify UHF and VHF signals separately or combined, and it has an FM trap. I've always used preamps such as this in fringe or near fringe areas with excellent results. If you live close in to any transmitters, be careful. It has a lot of gain.


Does it have any gain control? I live about 46 miles (as the crows fly) from the nearest tower in SF.

Scott, I looked at the installation of the CM7777 and see that the power inserter is mounted indoors. In my case I have the spliter outdoors. Does the spliter have to be after power inserter or can it be before the power inserter?

Edited by hobie346, 13 May 2009 - 12:21 PM.


#18 OFFLINE   Scott in FL

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Posted 13 May 2009 - 10:52 PM

No, it doesn't have gain control, but 46 miles from the transmitters in SF should be far enough away. You might be able to get by with a cheaper solution. But if I were you, and lived 46 miles away from the transmitters, I'd go for the CM7777.

Aren't there TV stations in San Jose? Be careful... they could overload your preamp.

There are splitters that pass DC, and splitters that don't. Here is one from Solid Signal that should work well: http://www.solidsign....asp?prod=LPD-2

One side will pass DC, the other side won't.

#19 OFFLINE   hobie346

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Posted 14 May 2009 - 08:32 AM

No, it doesn't have gain control, but 46 miles from the transmitters in SF should be far enough away. You might be able to get by with a cheaper solution. But if I were you, and lived 46 miles away from the transmitters, I'd go for the CM7777.

Aren't there TV stations in San Jose? Be careful... they could overload your preamp.

There are splitters that pass DC, and splitters that don't. Here is one from Solid Signal that should work well: http://www.solidsign....asp?prod=LPD-2

One side will pass DC, the other side won't.


Thanks for the info.

#20 OFFLINE   Davenlr

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Posted 16 May 2009 - 06:33 PM

Basically...you subtract the amplifiers noise figure and match/balun loss (if used) from your antennas gain to get the system gain of the antenna. Then you match your preamps gain figure to match or be slightly higher than the loss from coax+splitters+gounding blocks. This will prevent overload. If you do end up with an amp with more gain than needed, you can insert a higher loss splitter, attenuator if needed to compensate. The amp will replace the front end agc of the tv tuner.

I use a cm7777 here in a metro area, with a 15db gain uhf, and 12db gain vhf high yagi feeding it. It works well, unless pointed directly at the local 5 megawatt uhf tower, which will be going away June 12th. I can pick up all locals, as well as several 60-90 mile away stations, depending on atmospherics.

#21 OFFLINE   kokishin

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Posted 16 May 2009 - 09:42 PM

I use the CM3044 to distibute my OTA signal to two HR20s and it works very well. Without it, I was getting pixelation on a couple of distant OTA signals. With the CM3044, no problem. Even though I only have two HR20's, I purchased the CM3044 to allow for the addition of two HR21/AM21's. CM also makes other versions with different number of outputs up to 8 outputs. My OTA antennal installer was going to sell me the single output CM3042 with a passive splitter but instead I went to Frys and purchased the CM3044 and did not use a splitter although you can use it in conjunction with a passive splitter at your TV's if that is more convenient. Scroll down to the bottom of the page: http://www.channelma...amplifiers.html

Any suggestions for an OTA antenna signal spliter? I did a search on SolidSignal but nothing useful.

TIA.



#22 OFFLINE   Davenlr

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Posted 17 May 2009 - 01:41 AM

Distribution amp splitters are a good choice if all your signals are strong at the TV end of the feed from your antenna, as they will subtract their noise figure from the signal level at the end of the coax, and then split the signal with enough gain to eliminate the splitter loss. If you have a marginal signal, and dont purchase a GOOD distribution amp, its noise figure could subtract enough gain from your feed to render the weak stations signal lower than the noise floor, so when it hits the amplifier section, it amplifies the noise, and the desired signal is lost (I have a Radio Shack distribution amp that does just that). Channel Master makes some of the best low noise circuits on the market.

You can use TVfool.com to get your list of local stations, paying attention to the actual signal strength of the station in NM(DB). Taking my weakest station, which is UHF ch 18 at 1.2 DB as an example:
No Amp:
1.2db + 11.5db (antenna) = 12.7db
12.7db - 5db coax run loss = 7.7db
7.7db - 7.4db (4 way splitter) = .3db signal to tv agc
(This results in a signal quality reading of approx 12% and no lock on my best receiver)

Distribution Amp:
1.2db + 11.5db (antenna) = 12.7db
12.7db - 5db coax run loss = 7.7db
7.7db - 3.5db (CM3044 dist amp noise figure) = 4.2db signal to Dist amp section
(This signal level would be right at the margin point depending on tuners sensitivity)

Mast Mounted Amp
1.2db + 11.5db (antenna) = 13.7db
13.7db - 2.0db (amp noise figure) = 11.7db
11.7db + 26db (amp gain) = 37.7db
37.7db - 5db (coax) - 7.4db (4 way splitter) = 25.3db at tv
This signal results in a quality reading of 85% on my receiver.
Compare this to 59.2db which is the strongest stations signal available at my antenna, and does not cause overload on the mast mounted amp.

As you can see, for THIS situation, the distribution amp would not work if I wanted this station. You can easily do these calcs yourself, using the tvfool.com signal levels at your location, adding your antennas gain (in dbd, not dbi), and subtracting coax loss. This will let you decide if the mast mounted amp or distribution amp would be the better choice for you. You really should have about 10db at the receiver for a consistent signal, in all weather conditions. I am not taking into account any multipath amplification, which can really muck up a HR20's tuner, but doesnt seem to bother the AM21s tuner (or any of my other tuners).

Additionally, if you are trying to pick up a station with a TVfool signal reading LESS than 0, you can SUBTRACT the mast mounted amps noise figure from the TV stations signal level (say 2.0 for the amp, and -7db for the station) to get -9db. In order to receive this station, you would need to have an antenna with a minimum of 10db to kick the signal level high enough for the mast mounted amps gain to have enough signal to amplify. If you had a 7 db gain antenna, you would be at -2db (below the noise floor) when you hit the amp section, resulting in 26db of noise at the receiver, and no signal at all.

Edited by Davenlr, 17 May 2009 - 01:51 AM.


#23 OFFLINE   IDRick

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Posted 18 May 2009 - 03:12 PM

Davelnr, can you also help me with the calcs? I am using a DIY antenna so don't know the antenna gain nor have I finalized antenna installation. But, I have performed several tests using a temporary antenna mount on the roof along with a 25 ft lead, converter box, and an old analog tv. My converter box has both signal strength and signal quality meters. Using pad attenuators, I developed a regression equation for predicting margin to drop out on my temporary system. Tvfool overestimates signal strength in my area. Margin to dropout ranges from 30 to 45 dB for the major networks. Two UHF and one VHF stations are in the 40 dB range. I have three other low power UHF stations with 15 to 25 dB margins to dropout but these stations are only standard def digital and currently available on D* (CW in HD and the religious stations in SD).

Assuming I switch to Directv, I would have 150 ft of cable run total in the system (loss of ~9dB). I will have one two way splitter to send the signal to two HD tvs. I'm not sure of the best way to then proceed with the calculations... Do I assume a 3.5 dB loss per AM-21 (we would need two 21's)? I could add two a/b switches to allow temporary direct feed if the directv system is down (living room) or allow recording to a computer (my study). Assuming the AM-21's are similar to a common 2-way, my total system loss would be ~21.5 dB (9 dB cable + 10.5 dB splitters + 2dB a/b switches). Do you agree with these calcs? Which pre-amp would you recommend in my case? I'm leaning toward a Winegard 4700, (UHF only pre-amp).

thanks!

Rick

#24 OFFLINE   Davenlr

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Posted 18 May 2009 - 03:58 PM

Your calcs sound right. There is also a built in 3.5db loss inside each AM21 (two tuners). Since your signal at the antenna appears good, either Winegard or channel master mast mounted amps should work, they both offer higher gain than your system loss.

In my case, I cant even get a signal from my low power digital to register on my receiver without the amp.

I dont have any experience with Winegard, so just pay attention to the noise factor. As long as its low (under 3.5), and its gain is over 25, you should be ok for your stations 20 or higher.

If you need to reduce loss, consider RG11 instead of RG6 for that long a run.

#25 OFFLINE   IDRick

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Posted 18 May 2009 - 04:10 PM

Thanks davelnr! The Winegard 4700 has a NF of 3.0 and gain of 19 dB. NM for my strongest station increases by 5 dB post transition. It is a VHF station and I believe that I would reduce my risk of pre-amp overload by purchasing a UHF only pre-amp.

Have a great day! :)

Rick




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