# OTA signal strength/pixalization question



## Jim Parker (Aug 12, 2003)

Anchorage just got it's first OTA HD station!  Channel 2, NBC KTUU, has its new digital transmitter up. Channel 11, CBS TKVA also has its digital transmitter running, but in SD mode. Channel 5, UPN has had a low power digital transmitter running for a year or so. That's the good news.

So, I got a roof top antenna and installed it Tuesday. I hooked it up to the 921 and adjusted it for maximum strength on channel 2. The 921 shows a signal strength of 90. The transmitter for 2 is 22 miles at an angle of 342 deg, 11 is 5 miles and just happens to be perfect alignment with 2 at 342 deg. UPN is 5 miles at an angle of 80. KTUU is transmitting on channel 10 (VHF), UPN is transmitting on 22 (UHF).

Now for the bad news.  I am getting terrible pixalization, with some every 1 to 2 minutes and a complete loss of signal every 5 to 10 minutes that lasts for 5 to 10 seconds. Both 2 and 11 have the problem, but UPN does not.

I hooked the antenna to the digital input on the TV and had a rock solid picture for the 1 1/2 hours that I watched.

The antenna is a Tandy CS1100, which is intended for deep fringe areas. The local electronics supply house has a chart put together for Anchorage that recommends a CS900 or CS1000 for my area. They were out of the CS1000, so I went to the larger size. There is a school 300' to the north of me that has a sloped metal roof that is 10' higher than my antenna. It is directly between me and the transmitters for 2 and 11. There are no hills or other obstructions. Web page for the CS1100:

http://www.antennacraft.net/pdfs/CS1100.pdf

So, any ideas on why 2 and 11 are breaking up? Is a signal of 90 enough? Is it because the 921 is a POS? :nono2: Is it the metal roof? The TV locks onto the signal just fine.


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## jergenf (Mar 31, 2005)

> *Anchorage*
> KDMD PAX 33.n 6
> KTVA CBS 11.n 28
> KYES UPN 5.n 22


Don't see KTUU listed yet so I don't know the digital frequency for chan 2.

The problem you're describing sounds like fade. Usually fade occurs to people in a valley situation or when the antenna is near ground level. The sun heats the ground and causes hot spots (imagine the wavy heat pattern coming of a highway).
TV signals actually bounce of hot points from the terrain like a rock skipping on water. Anyway this can cause you to receive the signal multiple times at once but electrically out of phase which actually causes the two signals to electrically cancel each other out. The classic pattern is that the signal dropouts occur repeately like clockwork. This happened to me and I only was 5 miles from the transmitter and even occured on my stronger channels.

Suggest you raise you're antenna. If that's not possible try adding a preamp (19db), that worked in my case. Also perform a manual antenna alignment. You'll need a second person to move the antenna. Or if you have a portable TV that you can bring to the roof, then run another coax from your chan 3 output and use your remote to change your menu screens. For manual adjust do menu 6-8 then select "add DTV" and enter the digital frequency, example for 5 enter 22.

With digital stations it can be harder to align because all you have to go by is the signal strength meter where with analog you can actually see the picture getting better or worse.

Are you getting any ghosting on any of your analog stations? That may answer a possible problem with the building with the metal roof situation.


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## Jim Parker (Aug 12, 2003)

KTUU (analog channel 2) is transmitting the digital signal on channel 10.

Is fade a problem with digital? I thought that digital was supposed to be immune to many of the analog problems. I have the antenna about 30' in the air. I have tweaked the alignment to get the strongest signal for KTUU. What I am most concerned with is NBC in HD. The KIMO transmitter, the ABC station, is going to use the same tower as KTUU, so I am worried that I will have a problem with it when it starts transmitting HD in a year or so. UPN does not have any programs that I watch. 

Checking for ghosting on analog is a good idea. Ten years ago when I moved into this house, I installed an old antenna on the roof to use until I could get cable hooked up. There were terrible double and triple ghosts on all of the OTA channels. I'll check the analog signal with both the 921 and the TV with the new antenna.

The fact that the TV does not have a problem but the 921 does makes me wonder if the problem is the 921. I have 3 HD TVs with digital tuners. I might connect the antenna to other two to see what I get.


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## jergenf (Mar 31, 2005)

Jim Parker said:


> KTUU (analog channel 2) is transmitting the digital signal on channel 10.
> 
> Is fade a problem with digital? I thought that digital was supposed to be immune to many of the analog problems.


Fade is a situation where the carrier dims and brightens so the digital information is fluctuating along with it. All you need to loose is a single zero or one and the tuners needs to reverify the data stream again. So digital transmission display it even worse then an analog would. Ghost can be another problem for 8VSB but I beleive they have built better circuitry over the years to differeniate multiple data streams. So unless your ghost are moving or multiplying today's tuners are less supseptible.

BTW if it is fade you might be able to see it in the signal strength bar dip over a long periods of viewing (when in the manual adjustment menu).

Like I said the preamp cured my problem of frequent and even rythimic dropouts.
But I have a new antenna (CM4228) that I'm going to try and also plan to raise my mast to 30 feet and add a rotor. But that's for getting distant stations hopefully.



Jim Parker said:


> The fact that the TV does not have a problem but the 921 does makes me wonder if the problem is the 921. I have 3 HD TVs with digital tuners. I might connect the antenna to other two to see what I get


The OTA tuner in the 921 probably isn't as sensitive as some standalone STBs. Try your other HDTV and report your findings.


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## Bradtothebone (Aug 11, 2003)

Jim,
Using the portable TV to check for analog ghosts is a good idea. Your problem could be multipath, and simply peaking for greatest signal strength may not be the answer. At 90 signal strength, you might be seeing the sum of two strong signals (primary and "ghost"), but at some lesser "strength" you might be seeing more of the primary and less of the "ghost." Use the analog to set your antenna for the least "ghosty" picture, and see what you get on the digital. The 921 is not known to be a great DTV receiver; it's an earlier generation than probably most of the integrated HDTV's have.

Brad


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## Jim Parker (Aug 12, 2003)

What is a typical range for the signal strength of OTA channels?

I've been trying some things. 

There is only a small amount of ghosting on analog channel 13 on the TV, all others do not have any ghosting. 

The picture quality of the analog is better on the 921 than the TV. The TV has a herringbone pattern to most of the channels.

I put in a preamp and the signal dropped from 90 to 70. Increasing the gain causes the signal to go to 0.
Turning off the FM trap causes the signal to go to 0. Changing to a different preamp set to a minimum gain, the signal increases to 95. Increasing the gain or turning off the FM trap causes the signal to go to 0.

Even with a higher signal, the pixelization is worse with the preamp.

Turning the antenna 20 degrees to either side drops the signal to 70, but has little effect on the pixelization.


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## JD Robinson (Nov 13, 2004)

In my limited experience, if a preamp *hurts* the situation, that definitely points to a multipath problem. I actually had to switch to a less sensitive (but more highly directional) antenna to solve that problem.


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## Jim Parker (Aug 12, 2003)

I had another thought. There is an FM radio tower with several stations that transmitt from it about 1 mile from my house at an angle of 40 degrees. Maybe the FM signals are causing interference. That would explain why turning off the FM trap on the preamp causes the signal to go to 0.

I don't know how I could verify that this is the cause. Anybody have any ideas?

AVS has a thread on antennas that is about 90 pages long. Guess I will browse thru it.


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## jergenf (Mar 31, 2005)

Jim Parker said:


> I had another thought. There is an FM radio tower with several stations that transmitt from it about 1 mile from my house at an angle of 40 degrees. Maybe the FM signals are causing interference. That would explain why turning off the FM trap on the preamp causes the signal to go to 0.


Which channels are affected by turning off the FM trap?
If it's the PAX station it would make best sense since channel 6 borders the FM band. But for thoses channels in the UHF range I could not offer any explaination.


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## Jim Parker (Aug 12, 2003)

Good question. I had the 921 on KTUU HD (transmitting on channel 10) when I had the preamp installed. I'll check the other channels.

KTVA 11 (transmitting on 28) also has a lot of pixelization, but UPN on 22 does not. Both of those are well away from the FM band.


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## ClaudeR (Dec 7, 2003)

Yes, the tuner in the 921 is a POS. I have to use the satellite locals because OTA fades too much.


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