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post #1 of 34 Old 06-11-2011, 05:54 PM - Thread Starter
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I've got a rooftop antenna, which I had installed about three months ago. The picture was so good that I had the same guys who installed that came back out last week to set up a distribution amp with a feed to three rooms; we had still been using tabletop antennas in the back room and that seemed silly with a nice antenna on the roof. After they hooked everything up we flipped through the channels quickly and everything looked okay. After they left, though, I noticed some channels cutting in and out so I started looking at signal strengths. All of the network transmitters (ABC, NBC, CBS, PBS, Fox) are in the same place and relatively nearby, which makes my area great for antennas. Before, the set that was connected to the rooftop antenna had a great signal on all of those channels. Now, however, we are getting a very weak signal on some of those channels on all of our sets, especially NBC and Fox. The others are still coming in very strong. I'm wondering if that pattern of a very strong signal on some channels and not on others will tell someone smarter than me what the problem likely is. The "real" channel numbers of the bad channels include 29 and 31. Channels with higher and lower numbers are okay. The amp I used was this http://www.amazon.com/gp/product/B001EKCGT8. I am feeding it power down one of the coax runs using this inserter http://www.amazon.com/gp/product/B002R6PTWY. Does this look like an installation problem or a hardware problem?
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post #2 of 34 Old 06-11-2011, 06:21 PM
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Just a guess by the RFs you gave...are these Chicago channels? If so, that is odd because WMAQ and WFLD are among the strongest in town.
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post #3 of 34 Old 06-11-2011, 07:09 PM
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I use the 8-port version.

Not sure why you are using a power inserter. As far as I know the coax for power is only for power, there is no RF in it.
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post #4 of 34 Old 06-11-2011, 07:15 PM - Thread Starter
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No, I'm in VA. Although the stations are close and strong. I'm getting a decent signal off of them using a Terk indoor antenna... much better, on those particular stations, than from my rooftop antenna and amp.

On mine, you're able to have one feed that carries power into the distributor and RF out. Saves a cable run.
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post #5 of 34 Old 06-11-2011, 08:18 PM
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Maybe the rooftop antenna needs a bit of re-aiming. Put your zip code into AntennaWeb and it will show you where the signals come from. Might also check to see if the antenna has the optimal pickup pattern.
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post #6 of 34 Old 06-12-2011, 03:59 AM - Thread Starter
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Quote:
Originally Posted by Roger Dressler View Post

Maybe the rooftop antenna needs a bit of re-aiming. Put your zip code into AntennaWeb and it will show you where the signals come from. Might also check to see if the antenna has the optimal pickup pattern.

I guess that isn't impossible, but I've got a good signal on a channel whose transmitter is 244 degrees at 12.5 miles and a weak one from a transmitter that is at 248 degrees at 12.6 miles. Seems like too sharp of a drop-off to be the antenna.
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post #7 of 34 Old 06-12-2011, 06:56 AM
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Probably overloading the amplifier.
Have you tried an attenuator on the input?

Also, it's possible that the amp is driving the TVs too hard. You could first try an attenuator on one TV set, and see if that fixes that one.

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post #8 of 34 Old 06-12-2011, 07:17 AM
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Please post a TV FOOL report. This will give a better idea of your situation & help us to make recommendations.

Also, do you know which model antenna you are using? If not, can you post a picture?
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post #9 of 34 Old 06-12-2011, 07:37 AM - Thread Starter
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Quote:
Originally Posted by kenglish View Post

Probably overloading the amplifier.
Have you tried an attenuator on the input?

Also, it's possible that the amp is driving the TVs too hard. You could first try an attenuator on one TV set, and see if that fixes that one.

I tried unplugging the amp to see if that helped the situation and it didn't; made it worse, in fact (although I'm still getting a good signal on most channels, even with no power to the amp). But I'm so much in the dark about this stuff that I'm not sure if that has any relevance to what you suggested.
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post #10 of 34 Old 06-12-2011, 07:48 AM
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Quote:
Originally Posted by Dimdem View Post

But I'm so much in the dark about this stuff that I'm not sure if that has any relevance to what you suggested.

Unfortunately, until a TV FOOL report is posted, we are in the dark just as much as you are.

Attenuators are not even in the picture yet. (No pun intended)
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post #11 of 34 Old 06-12-2011, 08:05 AM - Thread Starter
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Quote:
Originally Posted by Digital Rules View Post

Unfortunately, until a TV FOOL report is posted, we are in the dark just as much as you are.

Attenuators are not even in the picture yet. (No pun intended)

http://www.tvfool.com/?option=com_wr...001b403f8e0e66

Edit: As you can see from this, all of the worthwhile stations are within a few degrees from each other and within a 1/10 of a mile in distance. Also maybe worth repeating is that I had been getting a good signal on all of these stations until the amp was added, although admittedly I hadn't watched any TV recently. Later today I will hook a TV directly to the antenna feed, before it gets to the amp, to verify that the antenna itself is still pulling in a strong signal on all stations.
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post #12 of 34 Old 06-12-2011, 08:19 AM
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Do you know what model antenna was installed or can you possibly post a photo of it?

While the amp you have deals well with strong signals, you really shouldn't need an amp with the right antenna.

Also, which channels are giving you problems?
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post #13 of 34 Old 06-12-2011, 08:33 AM - Thread Starter
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Quote:
Originally Posted by Digital Rules View Post

Do you know what model antenna was installed or can you possibly post a photo of it?

While the amp you have deals well with strong signals, you really shouldn't need an amp with the right antenna.

Also, which channels are giving you problems?

http://www.amazon.com/gp/product/B00...ohs_product_T2

It is the NBC and Fox stations that are giving me issues.
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post #14 of 34 Old 06-12-2011, 08:49 AM
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Go ahead & re-try the antenna hooked directly to one set & see if reception improves. The selected antenna is excellent & should easily power 4 or more sets without amplification.
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post #15 of 34 Old 06-12-2011, 09:24 AM - Thread Starter
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Yep, signal directly from the antenna is excellent on all channels; just checked. At this point, could it be anything besides a bad distributor amp? Could there be any problem with the coax cable that would affect channels so selectively? I take your point that maybe I don't really need the amp at all, but if I unplug the power to the amp it is just a splitter, right?
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post #16 of 34 Old 06-12-2011, 09:36 AM
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Quote:
Originally Posted by Dimdem View Post

...I unplug the power to the amp it is just a splitter, right?

Nope. It's active component is a semi-conductor that generally will not conduct when not powered. You need to replace it with a splitter. It is unlikely that you need amplificaton for the Washington, DC stations. It is possible that a local FM rasdio station is overloading your amplifer, but before we explore that possibility, you should just replace the amlifier with an inexpensice splitter or two t see if that makes the problem go away.
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post #17 of 34 Old 06-12-2011, 09:40 AM - Thread Starter
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Quote:
Originally Posted by AntAltMike View Post

Nope. It's active component is a semi-conductor that generally will not conduct when not powered. You need to replace it with a splitter. It is unlikely that you need amplificaton for the Washington, DC stations. It is possible that a local FM rasdio station is overloading your amplifer, but before we explore that possibility, you should just replace the amlifier with an inexpensice splitter or two t see if that makes the problem go away.

I'd need more than a amplifier for DC stations; that's over 100 miles from here. But I can try it with a splitter. Right now the signal goes to three rooms; would be I better off with a three or four way splitter? Seems like someone once told me not to use a three way one, but they didn't explain why.
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post #18 of 34 Old 06-12-2011, 10:02 AM
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You are attempting to get the Tidewater stations, not DC; correct? The DC stations are out of reach for reliable reception.
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post #19 of 34 Old 06-12-2011, 10:09 AM - Thread Starter
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Right, these are the Tidewater/Hampton Roads stations.
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post #20 of 34 Old 06-12-2011, 10:33 AM
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Quote:
Originally Posted by Dimdem View Post

I'd need more than a amplifier for DC stations; that's over 100 miles from here....

Oops. When you said "Virginia" in an earlier post, I interpreted it as northern Virginia (AKA, civilization).

You do NOT need an amplifier for any of your stations that are twelve miles away.
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post #21 of 34 Old 06-12-2011, 12:02 PM
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Quote:
Originally Posted by Dimdem View Post

Later today I will hook a TV directly to the antenna feed, before it gets to the amp, to verify that the antenna itself is still pulling in a strong signal on all stations.


Replace the amp with something like this.

http://www.amazon.com/Philips-PH6104...7905257&sr=1-3
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post #22 of 34 Old 06-12-2011, 01:08 PM - Thread Starter
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Wow, hard to beat $587 savings. Thanks.

Edit to add: Even if using an amp was overkill, is the kind of problem that I experienced what you would expect from using one in my situation? I guess that eliminating the amp will solve the problem even if the issue was a defective amp, but I'm just wanting to make sure that there is no reason to suspect something else was the real cause, like a problem with a cable.
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post #23 of 34 Old 06-12-2011, 09:42 PM
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Even if using an amp was overkill, is the kind of problem that I experienced what you would expect from using one in my situation?
Yes, because you are overloading the amp with your very strong signals. If you go here to Solid Signal for the CM3414 (which is the same as the PCT-MA2-4P), and click on the specifications tab you will see the problem:
http://www.solidsignal.com/pview.asp...mplifiers&sku=

The specs say output level 18 dBmV and gain 8 dB, which means that the max input allowed is +10 dBmV, which is the same as -38.8 dBm. Your tvfool report for Norfolk gives the signal power of about -24 dBm for CH 29 & 31, which is about 15 dB too strong for the amp. For a more accurate estimate you would need to add the antenna gain and subtract the coax loss (6dB per100ft for UHF), but you get the idea. The most accurate way would be to measure the signal with a signal level meter and then to add some attenuation before the amp to make the signals a little weaker to find out where the amp would behave.

But, for your situation just try an ordinary 4-way or 8-way splitter instead of the amp. I use the 15-1235/150-1235 4-way splitter from Radio Shack for my experiments (not the more expensive satellite or bidirectional ones) if you want to try something right away, but you can buy one for a lot less if you order it online.
http://www.radioshack.com/product/in...ductId=2062051
http://www.radioshack.com/search/ind...0splitter&sr=1
Quote:
.....but I'm just wanting to make sure that there is no reason to suspect something else was the real cause, like a problem with a cable.
It is entirely possible to have more than one problem at a time. A short in the coax from a strand of the shield contacting the center conductor is very common.

If you can not measure it, you can not improve it.
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post #24 of 34 Old 06-13-2011, 04:24 AM
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Quote:
Originally Posted by Dimdem View Post

I've got a rooftop antenna, which I had installed about three months ago. The picture was so good that I had the same guys who installed that came back out last week to set up a distribution amp with a feed to three rooms;

Just curious, what made you think you needed an amp? Did the contractor suggest this?
Usually its common practice to add an amp only when you start adding other TV's AND you start noticing the picture dropping out, otherwise as others stated you risk overloading signal. With your location, you should have no problem feeding the other TV's without an amp. All you need is just a 3 or 4-way splitter.

My outdoor antenna is 24 miles away from the tower, and I feed 3 tv's with plenty of signal to probably feed more tv's in my house. All this with no amp.
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post #25 of 34 Old 06-13-2011, 06:10 AM
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Quote:
Originally Posted by rabbit73 View Post

...you are overloading the amp with your very strong signals.

Maybe we should put that in bold type:

...you are overloading the amp with your very strong signals.

You are not now getting weak signals at any TV with your over-amplified system even though the signal strength metering function in your tuners may say otherwise. Your tuner's signal strength meter is not a real signal strength meter. It provides a useful indication of signal adequacy, but the numerical value it displays is derived largely from, and varies inversely with, bit errors, which go up astronomically when an amplifier is overloaded, and result in the receiver calculating and displaying a low signal strength number.

Quote:
If you go here to Solid Signal for the CM3414 (which is the same as the PCT-MA2-4P), and click on the specifications tab you will see the problem:
http://www.solidsignal.com/pview.asp...mplifiers&sku=

The specs say output level 18 dBmV and gain 8 dB, which means that the max input allowed is +10 dBmV, which is the same as -38.8 dBm.

While we all agree that your amplifier is unnecessary and overloaded, the overload information provided with most consumer-grade amplification products is nearly useless. This amplifier is designed and furnished to amplify a large number of equal strength cable TV channels. You are amplifying a small number of broadcast digital channels, which, in your case, and to your benefit, are closer to equal value than those that most home antenna systems must deal with.

I would guess that the engineering data for that amp that was furnished to the sales department before they butchered it is that it can amplify a "full load" of about half, equal strength analog carriers (roughly channels 2-70) and the rest as digital signals which, if 256 QAM, are 6dB weaker than the analog signals (12dBmV), to maximum output level of 18dBmV as measured on an analog carrier at any of the four output ports. But that's just my guess.

As a simple rules of thumb, each time you cut the number of equal strength analog carriers in half, the maximum output goes up by 3dB, but there are other engineering considerations that confound any attempt one may make to calculate maximum permissible signal levels in digital and mixed signal level environments that go beyond the scope of this thread.

Ballparking, if that amplifier can amplify a load of 135 QAM channels to 12dBmV, then it could amplify 67 of them to 15dBmV, 34 of them to 18dBmV, 17 of them to 21dBmV, and 8 of them to about 24dBmV, which is closer to your channel load, But again, this engineering oversimplification does not take into account the fact that intermodulation disrupts and degrades weaker signals more than it does stronger signals, and with a scattered, broadcast channel load, it occurs at certain frequencies more intensely than at others.

Here is a way to ballpark calculate that you don't need an amplifier. Just about any receiver will work with a signal strength of about -83dBm, or -34dBmV. You have a field strength of about -24 dBm to -28dBm. for the local network stations you desire to receive, and they are increased in your system by unknown antenna gain, which we won't even bother to work into this estimate. You would theoretically lose 7dB through a 4-way split, and maybe 6dB per 100 feet of coax at your highest channel. You don't need a calculator to see that you would have over a thousand times as much signal as you need at each TV, even without using an amplifier.
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post #26 of 34 Old 06-14-2011, 07:24 PM
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Dimdem:

Please let us know how the amp, splitter, and grounding problems work out.

If you can not measure it, you can not improve it.
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www.megalithia.com/elect/aerialsite/dttpoorman.html
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post #27 of 34 Old 07-03-2011, 12:08 PM - Thread Starter
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No one will be surprised about this, I'm sure, but I wanted to confirm that replacing the amp with a passive splitter solved the problem.
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post #28 of 34 Old 07-03-2011, 03:15 PM
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No, not surprised. The amp was distorting the signal, which will sometimes make strong stations actually show weaker on some signal meters.
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post #29 of 34 Old 07-03-2011, 03:30 PM
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Quote:
Originally Posted by Dimdem View Post

I tried unplugging the amp to see if that helped the situation and it didn't; made it worse, in fact (although I'm still getting a good signal on most channels, even with no power to the amp). But I'm so much in the dark about this stuff that I'm not sure if that has any relevance to what you suggested.

Usually unplugging the amp will make it worse, as it won't simply pass signal. You'll have to completely remove it from the chain of coax.

Oops. Looks like you are all set.

'Better Living Through Modern, Expensive, Electronic Devices'

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post #30 of 34 Old 07-04-2011, 05:25 AM - Thread Starter
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Oops. Looks like you are all set.

Yep. Thanks again to all those who helped.
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