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Guest Message by DevFuse

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ota splitter


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12 replies to this topic

#1 OFFLINE   jwciv

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Posted 14 December 2010 - 01:18 PM

Hi - I have a terk antenna, mounted inside my attic, has RG6 running to an AM21 (about a 65 foot run), then into an HR23. I get great reception and signal strength, as displayed in the HR23 it is generally 90-100 depending on the channel. I plan on putting another TV in my bedroom soon, so I split the signal in the attic with a one-input, two-output 5-1000mHz splitter , 3.5db loss per leg. Went to watch OTA and got "searching for signal". I replaced the splitter with a barrell connector (on the AM21 leg) and my signlas were back up in the same range.
My question - do I need a wider mHz range to get OTA signal? I may have a bad splitter but did not want to bring it back and replace it with the same model if it's not correct for the application.

Thanks for your input

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#2 OFFLINE   rocket69

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Posted 14 December 2010 - 01:32 PM

those specs are in range for OTA but it could be that your splitter is bad or requires a powerd amp

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#3 OFFLINE   bt-rtp

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Posted 14 December 2010 - 01:41 PM

You have just enough antenna gain without the splitter to be within the threshold of the AM21 tuner. The splitter loss causes the signal to drop out of the threshold. You need to added a powered amplifer in the attic between the antenna and the splitter.

Of course it could also be a defective splitter, especially if it's an old one that has previously been in use outside. Moisture getting into the connections causes these to fail.
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#4 OFFLINE   jwciv

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Posted 14 December 2010 - 02:08 PM

with the AM21 showing signal in the 90s and up, would a splitter really drop it that much so that it is out of range?

#5 OFFLINE   rocket69

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Posted 14 December 2010 - 02:16 PM

it should not but if its defective or has been sitting around for 30 years.

Another thing if you have sitting around that might do you good is a Tap one leg in another that is (tap) and and one out at -3db. Hook up in to ant tap to am21 and out to other room .

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#6 OFFLINE   jwciv

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Posted 14 December 2010 - 03:16 PM

You have just enough antenna gain without the splitter to be within the threshold of the AM21 tuner. The splitter loss causes the signal to drop out of the threshold. You need to added a powered amplifer in the attic between the antenna and the splitter.

Of course it could also be a defective splitter, especially if it's an old one that has previously been in use outside. Moisture getting into the connections causes these to fail.


If I were to add an powered amplifier, should I be concerned about overdriving one leg - - the new bedroom TV is only a 10 foot run from the splitter as opposed to the 65' on the other leg.

#7 OFFLINE   Stewart Vernon

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Posted 14 December 2010 - 05:47 PM

with the AM21 showing signal in the 90s and up, would a splitter really drop it that much so that it is out of range?


Two things...

Most "signal meters" don't seem to be showing signal strength, but rather quality of signal-to-noise... so you could have a strong signal with lots of noise/multi-path OR a weak signal that is clean of interference, and get a similar "strength" on signal meters on most receivers/decoders/TVs.

A 2-way splitter that doesn't have amplification built-in... will by definition split the signal in half... so if the reason why you had a solid signal was because it was low but clean, then you might find reception gone entirely.

IF it was strong but noisy, then it might be strong enough after a split.

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#8 OFFLINE   jwciv

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Posted 14 December 2010 - 08:22 PM

went to Lowes tonight and bought an RCA amplifier, only one they had on the shelf was one input, four output, $19.99, advertised to raise signal 10db. It got my signal back on most channels on the AM21, but not all. Those that came back were only reading around 40-50 on the AM21 signal meter.

Now I'm confused - - my system worked fine prior to splitting. If I take out the splitter and just put a barrel connector in place it works fine (so all my new fittings are good). The splitter causes 3.5db loss and with it in place I lose all my channels. The amplifier, which does not require the separate splitter, boosts the signal 10db, but I still can't get all my channels. What gives?

#9 OFFLINE   Davenlr

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Posted 14 December 2010 - 08:30 PM

went to Lowes tonight and bought an RCA amplifier, only one they had on the shelf was one input, four output, $19.99, advertised to raise signal 10db. It got my signal back on most channels on the AM21, but not all. Those that came back were only reading around 40-50 on the AM21 signal meter.

Now I'm confused - - my system worked fine prior to splitting. If I take out the splitter and just put a barrel connector in place it works fine (so all my new fittings are good). The splitter causes 3.5db loss and with it in place I lose all my channels. The amplifier, which does not require the separate splitter, boosts the signal 10db, but I still can't get all my channels. What gives?


Those amps, while advertising 10db gain, usually fail to mention they also have a very high noise factor. The first thing I learned while getting my ham license was, if there is no signal (or just enough) to begin with, you cannot ampliify it. What you require, is a mast mounted amp on your rooftop antenna. This will boost the signal that is much stronger there, and that boosted signal wont all be lost in the coax cable, resulting in much more signal available at the end of the coax, where your 10db splitter (or a passive one) probably wont drop channels out on you. The best mast amps, like the channel master 7777, has about 25+db gain while only adding 1.5 or less db of noise, and the trip down the coax will eliminate the noise.

All this is assuming you have the max gain you can in the first place (good antenna, up as high as possible).

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#10 OFFLINE   Stewart Vernon

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Posted 14 December 2010 - 09:43 PM

Yeah, that's the tricky thing about amplifiers...

They amplify noise AND many also introduce new noise as well.

So back to my earlier post...

When your digital tuner indicates a high signal... it could be:

A. Strong signal, with noise

or

B. Weak signal, but free of noise

Both scenarios result in high signal-to-noise ratios and a good signal BUT each responds differently to a splitter and amplifier.

Scenario A, when amplified, can result in poor signal because the noise is also amplified... whereas Scenario B can result in stronger signal because there was no noise to be amplified.

Splitting Scenario A might still work because the signal was strong and you are splitting the noise as well as the signal, thus having the same signal-to-noise ratio after the split... whereas Scenario B is noise-free BUT when split might result in a signal that is not strong enough.

For ideal reception you want both a strong AND a clean signal... which can be hard to do especially across the whole spectrum of OTA channels in your area. You sometimes have to settle for a best-case configuration that gets the most channels OR optimize for your favorites.

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#11 OFFLINE   jwciv

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Posted 15 December 2010 - 09:53 AM

thanks everyone for the input. I'm going to start by ensuring I'm aimed correctly and getting the best signal I can, then figure out if I need a pre-amp or an amp. I have a feeling I'll end up returning the RCA amplifier and go with a pre-amp or amp that is commonly recommended on these forums, probably something from solid signal.

Besides my AM21, is there a better device to use for checking signal, or would I be talking about spending $300 for something like a birdog sat signal meter?
My Sharp Aquos also has a meter, but I'd guess that is about as useful as the AM21.

Edited by jwciv, 15 December 2010 - 05:00 PM.
too many typos


#12 OFFLINE   Scott in FL

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Posted 16 December 2010 - 03:36 AM

Yeah, that's the tricky thing about amplifiers...

They amplify noise AND many also introduce new noise as well.


All amplifiers introduce noise. There is no such thing as a noise free amplifier. Good pre-amplifiers have a low noise figure.

When you add 3.5 dB of attenuation before the front end of a tuner, you degrade the tuner's noise figure by 3.5 dB. Coax has loss too, which also degrades the tuner's noise figure by the amount of the attenuation. My guess is the splitter's 3.5 dB of attenuation degraded the system noise figure enough to drop the carrier-to-noise below the receiver's threshold.

Bottom line: You need a good quality, low noise pre-amp as others have recommended at the antenna (or at least before the splitter). Channel Master is an excellent choice.

By amplifying at the antenna, where the signal is strongest compared to the noise floor of the pre-amp, you achieve the maximum carrier-to-noise ratio. Coax and splitter attenuation after the pre-amp will attenuate the carrier and noise equally, but if the pre-amp's gain is adequate to overcome the coax and splitter loss, the signal at the input of the tuner will be high enough compared to the tuner's noise floor.

The amplifier's gain should only be high enough to make up for the loss between it and the tuner (which is comprised of the coax loss and splitter loss). And the pre-amp should have a low noise figure.

Finally, you don't want to overload the pre-amp's front end, so you must consider how close you are to transmitters. All of the signals that pass through a pre-amp add together and must be considered (TV, FM, UHF radio, etc.).

Edited by Scott in FL, 16 December 2010 - 03:45 AM.


#13 OFFLINE   jwciv

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Posted 20 December 2010 - 10:58 AM

turns out the amp in my Terk HDTVo is bad and I need to replace the antenna. When it was working, I was able to have a splitter in place and get all the channels I wanted (NBD, CBS, ABC, FOX) with a signal range of 70%-100% depending on the channel, so whatever the spec are on the Terk HDTVo, they seem to be adequate. However, based on all that I have read, Terk is not the best and I'd like to go with something else, here's my details:

zip: 01863
antenna mounted inside attic, approx 30' off the ground
info from antennaweb (could not get this to format all that well):

DTV Antenna Type Call Sign Channel Network City, State Live Date Compass Heading Miles From RF Channel
* yellow uhf WNEU-DT 34.1 TEL MERRIMACK, NH 352° 26.0 34
* yellow uhf WUNI-DT 27.1 UNI WORCESTER, MA 234° 26.8 29
* yellow uhf WZMY-DT 50.1 MNT DERRY, NH 12° 6.7 35
* green vhf WMUR-DT 9.1 ABC MANCHESTER, NH 352° 26.0 9
* red uhf WBZ-DT 4.1 CBS BOSTON, MA 176° 23.9 30
* red uhf WUTF-DT 66.1 TFA MARLBOROUGH, MA 212° 18.4 27
* red uhf WBPX-DT 68.1 ION BOSTON, MA 175° 24.7 32
* red uhf WGBH-DT 2.1 PBS BOSTON, MA 176° 23.9 19
* red uhf WCVB-DT 5.1 ABC BOSTON, MA 176° 23.9 20
* red uhf WMFP-DT 62.1 SAH LAWRENCE, MA 175° 24.3 18
red uhf W28CM 28 FMN NASHUA, NH 342° 7.0 28
blue uhf W33AK 33 FMN NASHUA, NH 350° 9.4 33
blue uhf WTMU-LP 32 TEL BOSTON, MA 157° 25.4 32
* blue uhf WHDH-DT 7.1 NBC BOSTON, MA 174° 24.2 42
* blue uhf WLVI-DT 56.1 CW CAMBRIDGE, MA 175° 24.7 41
* blue uhf WSBK-DT 38.1 IND BOSTON, MA 176° 23.9 39
* blue uhf WYDN-DT 47.1 DAY WORCESTER, MA 176° 23.9 47
* blue uhf WGBX-DT 44.1 PBS BOSTON, MA 176° 23.9 43
* blue uhf WFXT-DT 25.1 FOX BOSTON, MA 175° 24.7 31
* violet vhf WENH-DT 11.1 PBS DURHAM, NH 29° 38.2 11
* violet uhf WPXG-DT 21.1 ION CONCORD, NH 20° 37.8 33


looking for 4.1, 5.1, 7.1, 25.1 (highlighted in red). The worst case channel is FOX 25.1, blue antenna, I interpret that as medium directional with pre-amp, would appreciate advice on antenna models.
thanks!




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