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28-Jun-2012, 6:50 PM
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#1
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Member
Join Date: Feb 2012
Posts: 83
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How long can coax cables go and any conflicts before HDTV OTA signal losses?
Hello all.
What's the maximum coax cable lengths can be before they start losing signals from HDTV OTA feeds? Also, are there anything that can conflict them?
The reason why I am asking because I noticed some rooms, in a big house, can get more channels and better feeds than others. It could be the old coax cables (used to be for Dish service from the previous owners) or something. The house is about about 3,900 feet from the front yard, where the antenna is, to the back rooms. http://i.imgur.com/LTao8.jpg for an aerial shot from the sky.
Thank you in advance. 
Last edited by ant; 28-Jun-2012 at 7:03 PM.
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28-Jun-2012, 8:42 PM
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#2
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Location: Greater Seattle Area
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The answer is, "It depends".
RG-6 type cable has roughly 6 dB loss per 100 feet.
If the signal at the antenna is strong, let's say it has a NM value of 45.0 dB, you'll be able to theoretically connect 500 feet of cable (30 dB of loss) and still have a 15 dB fade margin at the far end.
On the other hand, starting with a weak signal such as your TVFR suggests, you can drive far less cable. Take as an example, KVCR real channel 26 which is predicted to arrive in the air at a NM of 8.1 dB. If you used a high gain antenna that had 12 dB of gain you would add the 12 dB antenna gain to the 8.1 dB giving you a NM of 20.1 dB at the antenna terminals. This is about 5 dB above what I consider a fairly conservative 15 dB fade margin, which means that if you add a 4-way splitter with 7 dB of loss, you'd leave the splitter with only a 13 dB fade margin and every dB of cable loss between there and the TV would drop you closer to the point of signal drop-out.
A preamp will help you if you have a weak but otherwise usable signal at the antenna. Preamplifiers and distribution amplifiers are used to 'push' the signal through lossy devises such as splitters and coax. Amplifiers do not and can not 'pull' more signal from an antenna.
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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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28-Jun-2012, 9:08 PM
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#3
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
The answer is, "It depends".
RG-6 type cable has roughly 6 dB loss per 100 feet.
If the signal at the antenna is strong, let's say it has a NM value of 45.0 dB, you'll be able to theoretically connect 500 feet of cable (30 dB of loss) and still have a 15 dB fade margin at the far end.
On the other hand, starting with a weak signal such as your TVFR suggests, you can drive far less cable. Take as an example, KVCR real channel 26 which is predicted to arrive in the air at a NM of 8.1 dB. If you used a high gain antenna that had 12 dB of gain you would add the 12 dB antenna gain to the 8.1 dB giving you a NM of 20.1 dB at the antenna terminals. This is about 5 dB above what I consider a fairly conservative 15 dB fade margin, which means that if you add a 4-way splitter with 7 dB of loss, you'd leave the splitter with only a 13 dB fade margin and every dB of cable loss between there and the TV would drop you closer to the point of signal drop-out.
A preamp will help you if you have a weak but otherwise usable signal at the antenna. Preamplifiers and distribution amplifiers are used to 'push' the signal through lossy devises such as splitters and coax. Amplifiers do not and can not 'pull' more signal from an antenna. |
Ah thanks. I just realized I have the wrong zip code entered. Ugh. It should be http://www.tvfool.com/?option=com_wr...1349a677fb8dec but then the results are still poor.  So yeah it was weird to see some channels vanished in some rooms and compared to directly to the antenna (short coax cable).
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29-Jun-2012, 5:38 PM
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#4
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
... A preamp will help you if you have a weak but otherwise usable signal at the antenna. Preamplifiers and distribution amplifiers are used to 'push' the signal through lossy devises such as splitters and coax. Amplifiers do not and can not 'pull' more signal from an antenna.
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A while ago, there was a coax cable connected to a power AC ( http://www.dennysantennaservice.com/...ed_352x298.jpg as an example online) in one of the small rooms (closest one to the main coax cable to the satellite dish and before its splitter in the attic) for the previous owners' Dish TV service. Is this a preamp? This was removed, so maybe this is why OTA does poorly in the rooms since this premap was removed? I wonder if we should put it back (not sure if it is compatible with OTA?), and it will work better?
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29-Jun-2012, 10:42 PM
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#5
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Moderator
Join Date: Oct 2010
Location: Greater Seattle Area
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Powered equipment from a satellite system installation is unlikely to pass OTA TV frequencies. Without knowing what the devise was, I can't say for certain. Connecting power to the coax incorrectly can put power into equipment that's not designed to receive it, possibly causing damage.
Because you're trying to distribute to several sets and you have weak signals at the antenna, a preamp such as the the Antennas Direct PA-18 or CPA-19 would be useful. It needs to install ahead of the splitter.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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29-Jun-2012, 11:05 PM
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#6
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
Powered equipment from a satellite system installation is unlikely to pass OTA TV frequencies. Without knowing what the devise was, I can't say for certain. Connecting power to the coax incorrectly can put power into equipment that's not designed to receive it, possibly causing damage.
Because you're trying to distribute to several sets and you have weak signals at the antenna, a preamp such as the the Antennas Direct PA-18 or CPA-19 would be useful. It needs to install ahead of the splitter.
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It looked like http://www.dennysantennaservice.com/...ed_352x298.jpg that I showed earlier. I will see if I can find it again and take a photo. of it later. All I remember was it in a closest/nearest room near the roof's old Dish connected to the attic's splitter with coax cables into four rooms. I don't think the attic has any power outlets, so it ended up in that room. Someone else said, in my alt.tv.tech.hdtv newsgroup thread, said it was for Dish receiver which make sense now. It seems like even Dish couldn't gets its singal far enough for those back/far rooms.
It looks like only Sears and Best Buy carry the preamps that you mentioned, but not currently in stock or unavailable. Any others that can be quickly easily and quickly purchased from and returned to Radio Shack, Fry's Electronics, Best Buy, Costco, Walmart, etc.?
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8-Jul-2012, 7:47 PM
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#8
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by ant
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I contacted Radio Shack through its web site a couple days ago and got this e-mail response/reply yesterday:
"Date: Sat, 7 Jul 2012 15:35:06 -0400 (EDT)
From: "RadioShack.com" <customerservice@radioshack.com>
To: Ant
Subject: Re: I need help finding a product
x-mailer: KANA Response 8.2.0.30.6
Dear Ant,
Thank you for contacting RadioShack.com.
We appreciate your inquiry and would be happy to assist. After careful
review of the products you've included in your questions, we believe we
have located all the information you require.
Our review indicates the products both do not work as a
pre-amplification device for your coaxial cable signal. The catalog
number 15-321 boasts a amplification of 40 decibels while the catalog
number 15-259 indicates the amplification is approximately 20 decibels.
At this time we have been unable to determine the measurement for
additional noise potentially generated by the devices..."
So it confirms that these amps are not for what I need for my situation.
[sighs] Sheesh, so hard to find a local retail store with pre-amps for OTA in Los Angeles/L.A. area.
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8-Jul-2012, 8:06 PM
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#9
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Moderator
Join Date: Oct 2010
Location: Greater Seattle Area
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Currently at Amazon:
The PA-18 for $28 http://www.amazon.com/Antennas-Direc...keywords=PA-18
And the more overload resistant CPA-19 (my recommendation) for $60 http://www.amazon.com/Antennas-Direc...eywords=CPA-19
Both offered with free shipping
The reports from independent testing of Radio Shack amplifiers makes me avoid them all-together.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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Last edited by GroundUrMast; 8-Jul-2012 at 8:08 PM.
Reason: I avoid Radio Shack amplifiers
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8-Jul-2012, 8:09 PM
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#10
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
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Local retail stores only, not online but thanks anyways.
Pre-Amp Newbie Questions: Do all pre-amps require power connections? Or are there actually pre-amps that don't require it? The reason for this is because the attic where the coax cables and splitter to the outdoor CM-4228HD antenna does not have a power outlet.
Last edited by ant; 8-Jul-2012 at 8:16 PM.
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8-Jul-2012, 8:18 PM
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#11
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Moderator
Join Date: Oct 2010
Location: Greater Seattle Area
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Preamps and distribution amps require power. Each design approaches the task in a unique way. Most preamps have an outdoor unit (the amplifier) and indoor unit(s) that connect power to the coax, sending the power up to the mast mounted amplifier.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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8-Jul-2012, 8:28 PM
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#12
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
Preamps and distribution amps require power. Each design approaches the task in a unique way. Most preamps have an outdoor unit (the amplifier) and indoor unit(s) that connect power to the coax, sending the power up to the mast mounted amplifier.
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So the coax connects to a power adapter too like Dish's coax cable to its power AC I saw a few months ago?
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8-Jul-2012, 8:31 PM
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#13
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Moderator
Join Date: Oct 2010
Location: Greater Seattle Area
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The illustrations in the installation instructions for the CPA-19 may be helpful. http://www.antennasdirect.com/cmss_f...structions.pdf
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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8-Jul-2012, 8:54 PM
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#14
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by GroundUrMast
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Thanks.
So, the amplifier (inside the attic? outside right next to the antenna?) would between the outdoor CM-4228HD antenna and the attic's splitter. Then, the power inserter (connected to a power outlet somewhere) would go between the amplifier and the four TVs.
Last edited by ant; 8-Jul-2012 at 9:56 PM.
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8-Jul-2012, 9:47 PM
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#15
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Senior Member
Join Date: Aug 2011
Location: USA Gulf South
Posts: 231
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Quote:
Originally Posted by ant
... Then, the power inverter (connected to a power outlet somewhere) would go between the amplifier and the four TVs.
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It's a power injector. A power inverter converts DC to AC.
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8-Jul-2012, 9:57 PM
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#16
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Member
Join Date: Feb 2012
Posts: 83
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Quote:
Originally Posted by MisterMe
It's a power injector. A power inverter converts DC to AC.
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Whoops. I misread that text on the diagram. Thanks.
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9-Jul-2012, 6:20 AM
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#17
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Moderator
Join Date: Oct 2010
Location: Greater Seattle Area
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Install the preamplifier as close to the antenna as is practical. This helps maintain the quality of the signal.
As signal travels further down the coax from the antenna, it gets weaker... but the low level noise produced inside the TV tuner does not get lower. This will leave you with less difference between the signal and noise (Signal to Noise Ratio). If the SNR is to low, the tuner can not recover enough error free data to display picture and sound.
Amplifiers can not 'pull' signal from the coax or the antenna. Amplifiers only 'push' the signal through the coax and splitter that is attached to the output of the amplifier.
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
(Please direct account activation inquiries to 'admin')
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9-Jul-2012, 6:23 AM
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#18
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Moderator
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This is the basic, most common layout.
Antenna ----> preamplifier ---------------------------> power injector ----> splitter ----------------------------------> TVs
Quote:
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...the attic where the coax cables and splitter to the outdoor CM-4228HD antenna does not have a power outlet.
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Here's another option which requires a special splitter. Use this if no power is available at the splitter: http://www.antennasdirect.com/cmss_f...itter_Opt2.pdf
__________________
If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
(Please direct account activation inquiries to 'admin')
Last edited by GroundUrMast; 9-Jul-2012 at 6:39 AM.
Reason: Added link to AD resources
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9-Jul-2012, 6:25 AM
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#19
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Member
Join Date: Feb 2012
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Quote:
Originally Posted by GroundUrMast
Antenna ----> preamplifier ---------------------------> power injector ----> splitter ----------------------------------> TVs
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Thanks again. I will have to find one from a local retail store in L.A. area.
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9-Jul-2012, 6:36 AM
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#20
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Moderator
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Double check my post #18 for edits
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If the well is dry and you don't see rain on the horizon, you'll need to dig the hole deeper. (If the antenna can't get the job done, an amp won't fix it.)
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