Help with pixelated picture despite excellent signal - UPDATED
 

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.

Tv Reception
 

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

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....

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?

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.

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.

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.

Tv Reception
 

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.

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.

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

Better, but . . .
 

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

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.

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.

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....

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...

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.

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.

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...

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.

Thanks for the additional suggestions. I moved the antenna to the other side of the chimney this weekend and my signal on channel 7 increased from 60 to 90. With our toddlers terrorizing the house, I haven't had a chance to see what affect this has on the picture quality. I'll update soon.

kb2fzq, I've tried hard to notice a pattern to the pixelation but haven't come up with much. However, we just don't watch enough TV to have a great sampling. But it seems to occur at all times of the day/night in a random pattern. I've started a record of each time it occurs to see if I can figure out a pattern. As far as RFI goes, I did unplug everything in the house (except the TIVO and receiver) and it didn't help. I'll try again by turning everything off at the circuit breaker and also turning off cell phones.

Tower Guy, can I get an HLSJ at Fry's. I assume L is the low input (which I leave empty) and then run cable from the high input to my TV? Will this mess up any of the other channels (major networks are all I'm interested in)?

I'm hoping the repositioning of the antenna with increased singly strength solves my problem. If not then, I guess it would seem to be an interference problem. I'll keep you updated.

Awww crap. I think I'm making things worse. So, with moving the antenna four feet to the other side of the chimney, channel 7 now has 89-93 signal strength (up from 60) and I haven't seen any more pixelation. Unfortunately, I now have pixelation on channels 2, 5 and 9. Channel 2, I can understand since the signal strength has dropped from 90 to 55-60 now, but channels 5 and 9 have signal strength of approximately 90 and are getting frequent pixelation. I'm still not sure whether I have a signal problem or interference problem. Interestingly, there was a bit of pixelation this afternoon (channels 2,5,9) but I haven't really seen any yet tonight. I'm really confused as to why I can't get a reasonable signal based on my TV fool report.
My next step is to try putting the antenna at the peak of my roof (not the chimney) to see if this makes any difference. Any other suggestions?

HLSJ=High (frequency VHF antenna) Low (frequency VHF antenna) Signal Joiner....HLSJ
The high side to the antenna, low side empty, the output (it will say "line") of the HLSJ to the TV...it's like a "T", the downward side of the T is the output..
This setup shouldn't bother anything else...

This might be an indication that the VHF portion of the antenna is not performing as well as the UHF portion of the antenna. Even though the signal strengths "in the air" are similar across channels, you are relying on different parts of the antenna to pick up VHF vs. UHF stations.



Signal meters on most receivers usually estimate signal quality as opposed to signal strength. In many cases, the value is related to the number of data errors being detected in the digital data stream. If too much data is lost or if certain critical portions of the data are lost, then the video stream cannot be properly reconstructed, and you end up with pixellation, macro-blocking, smearing, and/or dropouts. However, since there is no way of knowing exactly how your receiver computed the number 60 (there is no standard computation method), its impossible to tell how the signal meter reading relates to picture quality.

In most cases, there is no correlation between actual signal strength (power) and signal meter readings. That is, even a very weak signal might achieve a score of 100 if it is very clean. Conversely, a very strong signal might get a lower score (e.g., 60) if it is getting messed up by multipath interference, distortion, or noise.



Your neighbor's house and the surrounding trees do not appear to be that big of a problem. Trees and homes do create some multipath, but based on what is visible in your photo, your situation does not seem that bad.

BTW, it looks like some of the longer elements at the back of the antenna (the VHF elements) may be flipped the wrong way. Those click-in-place top/bottom elements are supposed to alternate. That is, if one element has the top piece going to the left and the bottom piece going to the right, the next element should have the top piece going to the right and the bottom piece going to the left. In your picture it looks like you have two of those elements in a row going in the same direction. You probably need to un-latch some of those pieces and flip them around to get them into the proper position. This is a common mistake since the installation instructions don't spell this out clearly enough.



No, that should not be necessary.



It would be interesting to see if fixing the antenna element positions changes anything.



The HLSJ is a diplexer with its frequency split in between low-VHF and hi-VHF. The high input passes everything from high-VHF and up (including UHF), so this should not disturb your reception on other channels.

BTW, the HD7694P only covers high-VHF and UHF, so it already has pretty low gain on low-VHF (which includes FM) frequencies. Adding an HLSJ will take out even more of the low-VHF signal. I'm just not sure how important this is.



If the interference comes and goes sporadically, I wonder if it is being caused by people talking on their key-up / key-down radios (e.g., ham radio operators, fire/police/ambulance, etc.). Do you have any police stations, fire stations, hospitals, or ham operators nearby that are in the path of your antenna?

I agree that your signals are very strong and should be very easy to receive cleanly. It is a mystery why you're seeing pixellation. Since nothing else seems to be fixing the problem, the next thing I would try is to attenuate the signal going into your receiver (with something like this). Supposing that there is a nearby transmitter that is causing interference intermittently, it might be introducing enough RF energy to overwhelm the front end of your receiver. If you attenuate the input signals, it might lower the RF energy enough to allow your receiver's front end to cope with the signals better (allowing the built-in AGC and adjacent channel rejection mechanisms to do their job more effectively).

Since the issue on VHF is solved, I don't feel the HLSJ or any attenuation is necessary. It is nearly impossible to overload without amplification. You would need to be less than 5 miles from transmitters (except FM) to experience overload in most instances.

The problem channels are all UHF now, so I suggest moving the antenna up/down a few inches at a time to find a sweet spot that works best for the remaining channels. It may take a bit of experimentation, but I find this quite effective time after time, especially when multipath is present.

Ordinarily, I agree that overload is not likely in a situation like this, but to continue to process of elimination, I wanted to test a few other hypotheses.

Most importantly, the inverted VHF elements should be fixed. By having some of the elements flipped around, it is quite likely that it is changing the gain and radiation pattern for VHF channels. It may also be introducing a slight amount of gain in frequency bands we don't really want. It's hard to say what shape the radiation pattern is right now and whether or not there is any increased gain on non-TV frequencies.

It is also possible for nearby first responder radio equipment to be operating in or near the TV spectrum (e.g., EMS dispatch can be on 155 MHz, WMTS can operate in 608-614 MHz, older legacy equipment might operate on vacant TV channels). If there are any police / fire / ambulance / hospital base stations directly in the path of antenna and very close, it might still be enough to overload the front end of the receiver.

A check of FM Fool indicates that there probably aren't any FM transmitters close enough to cause overload problems, but I don't know how close any of the other possible transmitters (police/fire/ambulance/etc.) are. Anything closer than a mile or two has the potential to cause problems.



Here are some of the clues that seem interesting:

1) The pixellation seems to appear on multiple channels spread across a broad range of spectrum at the same time. This would seem to argue against any kind of co-channel or adjacent-channel interference problems.

2) Moving the antenna from one side of the chimney to the other made VHF perform better, but made multiple UHF channels go bad.

3) There seemed to be some pixellation on multiple channels yesterday afternoon, but then there was a period of time in the evening when none of the channels showed any pixellation. This seems to imply that whatever is causing the interference came and went at around the same time across all of the channels. Is this pattern in any way related to human operators using or not using their radio at certain times of the day?



It would really help if we could attach a spectrum analyzer to this setup to see what's going on.

Before a quick update, I just would like to sincerely thank all of you for your thoughtful and helpful replies. I'm sure you all have other things to do than help troubleshoot my attempts to banish Comcast from my house.

When I moved the antenna to the other side of the chimney a few days ago, I aimed it to maximize channel 7 (the previous problem channel) but I didn't pay too much attention to the other channels. Today I changed the direction of the antenna (by about 20 degrees) so that all channels now get between 88-100 signal strength. I was getting pixelation frequently on channels 2,5, and 9 immediately before re-directing the antenna. After re-directing I saw NO pixelation on any channel for approximately 15 minutes. Unfortunately I didn't have time to watch longer and I'll be working tonight so I won't be able to check again tomorrow. I'm cautiously optimistic that I may be getting closer to a fix.

I still need to check the position of the antenna elements (as suggested by mtownsend) to make sure that they are flipped the correct way. If I'm still having trouble I'll try moving up/down as suggested by No Static At All and buying an attenuator. Interestingly there is a fire station directly in the line of the antenna approximately 1 mile away. Thanks again and I'll report back after more viewing time.

I'd be interested in what state, county and city that fire station is located in, and it's official title (such as "Smallville Fire and Rescue")...I will look up what frequencies they are using...that station may be your issue....

Menlo Park Fire Station
Station #1
300 Middlefield Road
Menlo Park, CA, 94025 (San Mateo County)

To test this theory, I could always start a small fire in the back yard and watch some TV as the fire department arrived :)

I just mapped the fire station to determine the distance from our house. It's 0.8 miles. It however is not directly in the line of the antenna. It appears to be a little less than 90 degrees off. I assume this is as bad?

Did you unfold all of the elements of the antenna before you erected it?

Menlo Park falls under the San Mateo county fire frequencies, which are 151 to 156 megahertz, channel 7 freq is 177 mhz...public services usually run some high power transmissions, and IF they are indeed interfering with you, you don't have to be in line of site to the culprit at 0.8 miles away, they will easily cover your reception at that distance, again "IF" it is them...
Other then a spectrum analyzer, which I'm pretty sure you probably don't have access to, a scanner with the fire frequencies for Menlo plugged in correlating the pixing with fire transmissions is the only way to prove it, that I know of....
I'll PM you the list...
And from looking at your area map, you seem to be in a metro area, there are probably more transmitters then you can count around your area, more bad news, freqencies can mix creating a different frequency, virtually impossible to find the frequency without a spec analyzer, I honestly hope the result of your issues is an easy answer...

So things are looking up - mostly. I haven't seen any pixelation since moving the antenna to the other side of the chimney and adjusting the direction. I've only had limited viewing time of about 15 minutes per day but haven't seen any picture problems on any channels during the day or evening.

Now for the bad news. Mtownsend was correct in noticing that the last set of elements (largest at the back) on the antenna were pointed the opposite direction so that they were not alternating with the other element sets. I fixed this. But while I turned one of the elements around to point right instead of left, the top metal bracket for the element fell off. The head of the pin keeping the bracket on top popped off. My wife can attest to the loud cursing coming from the roof. I reattached the bracket by wrapping both ends with bare metal wire to attach the top bracket to the bottom bracket (which the element in between). I though about using electric tape but didn't want anything with insulating properties. I really have no idea how the signal conduction from the antenna works. Is this likely to cause any significant problem? The signal strength seems OK on all channels except for channel 7, where it's about 82 (I think it was about 88 before). On the bright side, the picture currently seems OK in my limited viewing.

kb2fzq, thanks for the fire station info. I'm not sure what to do about it, except hope that it's not my real problem.

Miraculously, my picture quality problems seem to have been fixed. It appears that the combination of replacing all of the cable with new cable from monoprice and moving the antenna to the other side of the chimney did the trick. A big thank you to everyone who commented and offered advice. If you're ever in the San Francisco Bay Area, let me know so that I can buy you a beer :)