Help with pixelated picture despite excellent signal

cardinalfanrc · 25-Sep-2010, 9:02 PM

I just cut the cord from the cable company and installed an antenna but I'm having problems with the picture quality. The picture has brief pixelation lasting less than a second that occurs every minute or so. This happens on all of the major networks which are really the only channels that I'm interested in. My Tivo reports the signal strength as 93-100 on these channels. Here is the link to my TV Signal Analysis Report which shows excellent signal for all of the major network channels:

http://www.tvfool.com/?option=com_wr...a36220371cf285

I'm using a Winegard 7694P antenna mounted on my chimney at approximately 20-25 feet of the ground. It is pointed at 322 degrees from true north using my iphone. There are no splitters in the cabling although there is one connector to connect two pieces of cable together. The only possible obstruction is a neighboring house approximately 75 feet away that is in the line of sight for the antenna. It's a two story house (our's is one story) but the hight of the antenna is roughly the same height as the roof of the neighbor's house.

I'm confused as to why I have pixelation when I have good signal strength and the tvfool report shows that I shouldn't be having problems. Should I be looking at a different antenna? Is there any benefit to pointing the antenna up or down or raising it higher? Any suggestions would be much appreciated.

John Candle · 26-Sep-2010, 8:27 AM

Are you using a preamp or any other kind of amplifier? If so then disconnect them All. Remove them and have coax in there place. The signals are strong , and can overload amps.. What channels are the problem channels? Read and understand this-->http://forum.tvfool.com/showthread.php?t=695

kb2fzq · 26-Sep-2010, 11:26 AM

You might want to look around your area for radio frequency transmitters, such as cell towers, public service (police/fire), trucking companies, ham radio/CB antennas, anything that might transmit a high power RF signal...these signals could disrupt the TV digital data stream coming to your antenna, even if you're seeing a 93-100% signal strength, a high RF burst will disrupt the stream for just a nano-second, but enough to pixelate the picture....normally, this will happen on just a certain channel, but if the source is close enough and strong enough, it could be happening across all channels...
The pre-amp suggestion above should be your first step, if you're using one, remove it and just connect the down-lead to the antenna....at your distance to the transmitters, a pre-amp shouldn't be needed...and it may be "seeing" a stray RF signal...for example, if you can predict when the pixelation will happen, it could be a cell tower control channel searching for phones on a timed basis sending out a short, but strong signal every minute, zapping your reception for just that short burst....

cardinalfanrc · 26-Sep-2010, 3:01 PM

Thanks for the replies. There is no pre-amp. There also don't appear to be any other towers that would be emitting interference. It's certainly not an AT&T tower as my reception is horrible.

The pixelation appears to be happening on all channels. I really only watch the major networks and they all appear to affected. Watching football yesterday I had pixelation on channels 5.1 (CBS), 7.1 (ABC) and 11.1 (NBC)

Could this be related to cabling? I used my old cable company cable (which worked perfectly) with a piece of new cable connected with a coupler leading up to the antenna. If it's related to interference form some other RF signal is there anything that I can do to shield the antenna or fix the problem?

No static at all · 26-Sep-2010, 3:49 PM

I doubt it's interference if you are seeing the issue on so many channels. I would first suspect a cable or connection issue as the 7694 should work more reliably with the stations in the green. Do you know if there are any splitters in the system?

The only other thing I can think of would be multipath interference (signal reflections) which can cause even strong signals to pixelate. Did you ever have an outdoor antenna with analog TV? If so, if there was a lot of ghosting, that would indicate a multipath issue at your location.

Also, are you sure you have the antenna pointed correctly? The end with the reflector should be aimed towards the towers.

cardinalfanrc · 26-Sep-2010, 4:33 PM

Yeh, I've also been wondering if it's a cabling issue. There are no splitters in the cable but there is a F type connector connecting the original cable used with our cable TV to the new cable running to the antenna. I think I'll try buying a new 100ft cable for one single run from the antenna to the TV.

I have the antenna pointed with the smallest elements pointing towards the tower. I've been assuming that since my signal strength is 93-100 that the antenna is operating correctly and pointed correctly. Is this a reasonable assumption?

If there is multipath interference is there any way to fix this, such as a different antenna or some sort of shielding. Unfortunately I've never had a previous analog antenna to know if this has previously been a problem.

Keep the suggestions coming. I'll report back after replacing the cable.

No static at all · 26-Sep-2010, 4:42 PM

Yes, the smallest elements point toward the transmitters. The reason I asked is if an antenna is in fact pointed backwards, it can still work well with strong signals, but will be more likely to pixelate.

The multipath would have to be quite severe to be seen on so many channels, so I'm still leaning towards a cable/connection issue. The 7604 is an excellent antenna for your situation, so I'm sure you will work this out with a little more diagnosis.

John Candle · 26-Sep-2010, 8:37 PM

Unplug ALL electric and electronic devices through out the house and even out side. Unplug ALL transformers that power electric and electronic devices. Has the problem went away? If so , plug them back in one at a time until the interference generator is found. If the house has a door bell transformer , even that needs to shut off , when I say ALL I mean ALL.

cardinalfanrc · 26-Sep-2010, 11:04 PM

I unplugged all electrical devices (except for the stereo and Tivo connected to the TV) and this didn't make any difference. However, I just replaced the cabling and this may have solved the problem. Actually I just removed the second cable that was being used with a connector and ran a single shorter piece of cable through a window. I haven't seen any pixelation in about 15 minutes whereas I was seeing pixelation several time a minute before I changed the cable. When I changed the cable, the metal connector actually fell off and had to be pushed back on. I think that my current cable (from Fry's) in connection with the old piece of cable from the cable company may be the problem. I just ordered a new 100 ft cable from Monoprice. I'll post an update after the new cable is installed and I've had more time to see if the pixelation returns.

Thanks for all the advice and I'll keep you posted.

kb2fzq · 28-Sep-2010, 8:13 AM

If the F-connector "fell off" the old cable? That was your problem.....

cardinalfanrc · 4-Oct-2010, 1:34 AM

Thanks everyone for the help so far. So I replaced all of the old cable with a new 100' quad shielded cable from monoprice. This seems to have significantly improved the pixelation problem but doesn't seem to have fixed it completely. I watched TV on the major network channels (which is all I care about) for about an hour this afternoon. I saw no pixelation except for channel 7.1, which had several brief periods of pixelation. When I checked the signal strength on channel 7.1, it's about 60. This is a little odd because the signal strength from the other channels broadcasting from the same tower is about 90. I changed the direction of the antenna within a 45 degree arc and this didn't seem to make any significant difference in signal strength on any of the channels. So is a channel strength of 60 low enough to cause pixelation on my channel 7.1?

On a related note, now that I still have some pixelation with new cabling, I'm wondering if the problem is related to interference from trees and my neighbor's 2 story house. Below is a link to a picture taken from the level of the antenna. Basically the antenna is about the same height as the neighbor's roof and points pretty much right at the neighbor's house. Could this be causing the pixelation? I currently have a 10 foot mast. Should I try a taller mast to clear the neighbor's roof? Once again, any help is much appreciated.

http://picasaweb.google.com/ryan.col...96884694973026

No static at all · 4-Oct-2010, 2:43 AM

Did you try lowering the antenna a few inches as well ? I would try that before going higher, especially if only one channel is problematic. Does the signal level bounce around a lot when on channel 7?

Try to stay at least a foot from the metal cap on the chimney. The cap can have an affect at less than a foot, especially on VHF.

Also, do you have a sound bar or amplified speakers connected to the TV? I have seen them have an affect on VHF channels as well.

cardinalfanrc · 4-Oct-2010, 2:59 AM

OK, I'll try lowering the antenna a bit. I was just worried that it was pointing directly at the neighboring house. It's about 5 or 6 feet from the metal chimney cap so that shouldn't be a problem. My speakers are an onkyo 5.1 HTIB system. The speakers aren't powered but I suppose the subwoofer is. I'll try unplugging the subwoofer. Thanks.

kb2fzq · 4-Oct-2010, 7:48 AM

The middle frequency for channel 7 is 177 megahertz....public service radio is in the 155-164 mhz range....I still think that this is causing you the issues, but eventually, you'll find the culprit...also, just for grins, shut off and unplug your computer and see if the pixing stops...my computer will effect my WRGB channel 6 by a 20% SS drop if I don't sleep the laptop...just a thought....

cardinalfanrc · 8-Oct-2010, 5:20 AM

So now I'm starting to get a little frustrated. I'm still getting quite a bit of pixelation on channel 7. Turning off the computer and powered speakers (my subwoofer) as has been suggested has not made any difference. I haven't tried lowering the antenna to see if the signal increases but I plan to this weekend. Can someone tell me if the pixelation has anything to do with the fact that the signal on channel 7 is in the 60's while it's 85-100 on the other channels? Or is it more likely to be from interference of some kind? If there's interference from public service radio as kb2fzq suggested is there anything I can do to fix this. I'm running out of ideas and since we watch mostly ABC (channel 7) my wife is quickly loosing patience with my idea to cut the cord form the cable company. Any additional suggestions are much appreciated.

kb2fzq · 8-Oct-2010, 12:15 PM

Quote:

Originally Posted by cardinalfanrc

So now I'm starting to get a little frustrated. I'm still getting quite a bit of pixelation on channel 7. Turning off the computer and powered speakers (my subwoofer) as has been suggested has not made any difference. I haven't tried lowering the antenna to see if the signal increases but I plan to this weekend. Can someone tell me if the pixelation has anything to do with the fact that the signal on channel 7 is in the 60's while it's 85-100 on the other channels? Or is it more likely to be from interference of some kind? If there's interference from public service radio as kb2fzq suggested is there anything I can do to fix this. I'm running out of ideas and since we watch mostly ABC (channel 7) my wife is quickly loosing patience with my idea to cut the cord form the cable company. Any additional suggestions are much appreciated.

OK, let me answer the last question first...KGO 7 is only running 28.3 kilowatts of power, which IS normal for a VHF station, compared to the UHF stations very likely running much higher power, whereby your antenna/tuner will have a better signal quality on UHF(85-100% signal strength)....
My suggestion right off would be to adjust the antenna direction while watching channel 7's signal strength on the TV meter and getting the direction with the highest signal...a GPS or compass is only for general direction to the transmitter, fine tuning the direction of the antnna may be necessary in your case....it may be a PITA to communicate from antenna to TV, but is worth the shot...an addition of a rotor may be necessary...
Secondly, you didn't mention if your downlead coax is new or old, 75 or 300 ohm cable, the length of the cable and how many TV's you are running off the antenna, or if you have any splitters in the line....any or all of these could cause your issues with VHF....
Lastly, IF you are getting public service interference, you need to know who it is...that will take some investigation...
I had a similar pix problems here, I "assumed" it was interference from a cell tower a 1/4 mile from me...I put ferrite chokes on all my phase cables, and the problem disappeared, so there may be hope if it is a P.S. issue, but some answers to above would help to diagnose if it's you or someone else....
And additionally, I have a station 9 miles from me, channel 31-1, if I point at 204 degrees (albany, ny stations) , I will get a 60% SS, then it will drop out and back again, if I point right at the tower (234 degrees) I get a 90% SS, no drop outs...that little bit off could be your problem....tell the wife...be patient, we'll fix it...

No static at all · 8-Oct-2010, 12:36 PM

The 7694 is quite strong on VHF & should get that channel even sitting a few feet off the ground. I'm still thinking the antenna is sitting in a dead spot for channel 7 & just needs to be moved around a bit, plus check the aim as kb2fzq suggested.

Just 2 feet off the ground, I get 7, 8, 9, 11, 12 & 13 with a 7694 & some channels are much weaker than yours.

cardinalfanrc · 8-Oct-2010, 3:52 PM

Thanks for the help you guys. Unfortunately, I think my wife's patience is inversely related to the number of posts in this thread.

As far as the above questions go, I've tried aiming the antenna (left, right) while watching the signal strength and haven't been able to improve the signal. I haven't tried lowering the antenna or changing the pitch (up, down angle) but plan to try more re-positioning this weekend. It's currently mounted to the chimney but I'll try unmounting it and moving around the roof a bit. Did anyone get a chance to look at the picture I linked to to see if the neighboring house and trees might be an issue.

As far as the cabling goes, I gave a bit more detail in some of my above posts. I just replaced all of the old cabling with a single 100' 75 ohm quad shielded cable from monoprice. The single cable runs to one TV (through my Tivo box) with no splitters or couplers. The new cable seems to have fixed the pixelation on the other channels but not channel 7.

So I assume there's still no way to tell if the problem is with the signal strength or interference. And in reference to interference, what are ferrite chokes? Thanks.

kb2fzq · 11-Oct-2010, 7:58 AM

I looked at your antenna picture....I doubt that the trees or the house are blocking any signals, however, you are pointed right at your neighbors house, and if the neighbor is generating some sort of radio frequency interference, unbeknowns to them, it will effect your signal reception...is the pixelation occurring more at specific times of the day, for example, at 1 a.m. in the morning, is there no pixing? Yet, at 8 p.m. it's horrible? Also, is it a reciprocating pix, does it happen, say, every 30 seconds, or is it random?
This is important, there are many sources of RFI in homes these days....you might want to record when things are bad and when they're good, like when the neighbors lights go out for the nite, does the pixing stop or become reduced...some detective work is needed, as your description of your setup seems to be very good, you should be having no problems, especially at 26 miles from the tower, yet you are, something is interfering with the chan 7 signal...and I also suspect the RFI may be in your your own home, it might even be the TiVo box, as much of a pain it may be you should shut everything in your house off at the breaker box, (including cell phones) except the TV and TiVo and see if the pix stops...it could be something you never would have imagined was causing RFI...

Tower Guy · 11-Oct-2010, 3:05 PM

Quote:

Originally Posted by cardinalfanrc

I'm running out of ideas and since we watch mostly ABC (channel 7) my wife is quickly loosing patience with my idea to cut the cord form the cable company.

It could be FM interference. KQED is running 100 KW ERP on 88.5. To eliminate FM from the antenna, try a cheap HLSJ with nothing (or a 75 ohm terminator) connected to the L input.

Another possibility is airplane interference. (Your antenna is less directional on channel 7 than the UHF channels.) If that's the reason, a Y10-7-13 for VHF only would work better.