Problem 2 - LCD tv reception January 10, 2005, 08:35:02 pm Yahoo Message Number: 49095Here's a weird one for you....The factory installed LCD tv in our 2004 30'TB works fine when run off of the antenna (with the antenna booster on.) When we are hooked up to cable (with the antenna booster off), we get excellent reception on all 100+ channels EXCEPT for the five or six local stations (big network ones - ABC, CBS, NBC, etc.) We have a second tv in the bedroom (non-LCD type) and when we're hooked up to cable it works fine on all channels including the local stations.One theory we had was that the local station's signal was somehow different from the others and the LCD tv was somehow more sensitive and hence the poor reception.The second theory is that the antenna booster may not be working properly and even in the "OFF" position, the LCD tv is still getting some "boost" from it that shows up in the form of interference. If that were the case, why would it only affect the local stations and why not the second tv in the bedroom?The third theory is that the cable itself may be bad to the LCD tv and not the bedroom tv, but why would all the other channels come in so clearly?Any thoughts are appreciated.Chris W.
Re: Problem 2 - LCD tv reception Reply #1 – January 10, 2005, 08:56:03 pm Yahoo Message Number: 49100Quote we get excellent reception on all 100+ channels EXCEPT for the five or six local stations (big network ones - ABC, CBS, NBC, etc.) Can you add a bit more detail about what is bad about the local stations? Does everthing have a large shadow, perhaps with a vertical bar part way across the screen? Or is it full of light and dark bands (i.e., herringbone)? How close are you to the local transmitters? Is their signal very large? If it is shadowy with or without the bar, the problem is probably the local off air signal leaking into the LDC TVs antenna line on top of the cable signal. If you disconnect the CATV signal from the coach, do the local channels still look like a good signal (look for grain in the backgrounds and perhaps some snow). If snowy, the switch is working OK. If the signal looks really good, there may be a leak path somewhere, probably in the switch that turns on the antenna amp (it also switches the CATV signal to the TV set when you turn the antenna amp off). The switch may be bad or perhaps it is hooked up wrong.If the signal has a herringbone then my ability to suggest anything gets very poor. One finds that kind of thing with a lot of expermenting and some luck.Linley
Re: Problem 2 - LCD tv reception Reply #2 – January 10, 2005, 09:18:47 pm Yahoo Message Number: 49106Quote Here's a weird one for you.... "...EXCEPT for the five or Quotesix local stations (big network ones - ABC, CBS, NBC, etc.)..."Chris W. ChrisHave you gone to the TV's "Menu" and selected the channels you want to watch. Try doing the "Auto Select" routine.Steve S. Lazy Bones
Re: Problem 2 - LCD tv reception Reply #3 – January 11, 2005, 09:00:10 am Yahoo Message Number: 49130QuoteCan you add a bit more detail about what is bad about the local stations? Does everthing have a large shadow, perhaps with a vertical bar part way across the screen? Or is it full of light and dark bands (i.e., herringbone)? How close are you to the local transmitters? Is their signal very large? Thanks Linley for the great suggestions. The reception is just snowy with no obvious bars, lines, shadows or patterns. The sound is also affected and we hear a lot of static on only those channels with the poor reception. We are close to the local transmitters - probably within 5 miles as the crow flies. I'm not sure of their signal strength, but they are huge antennas that sit high on a hill and are visible for miles. I believe they serve the entire central Texas area around Austin. Since we've experienced this same problem while staying in two other RV parks in different parts of the state, not sure if that is a factor.We're not at the RV right now, but when we get back this weekend we'll try to isolate the LCD tv from the booster and see if that may be the problem.Chris W.
Re: Problem 2 - LCD tv reception Reply #4 – January 11, 2005, 09:51:38 am Yahoo Message Number: 49142QuoteThe reception is just snowy with no obvious bars, lines, shadows or patterns. The sound is also affected and we hear a lot of static on only those channels with the poor reception. We are close to the local transmitters - probably within 5 miles as the crow flies. You describe a LD antenna system that is working very well indeed if you get a very snowy picture that close to the TV transmitter. It is very well shielded and the switch is working well since all the other CATV channels are coming through OK. I don't really know what to expect but think, from your description, that the LD antenna system is OK. As a GUESS, the CATV system has moved the local signals to another channel to keep the signal leakage under control. Typical TV sets leak some so the local signal always has a shadow or bar on the screen so the CATV systems often places their signal on a different channel. I would follow up on what Steve S. suggested and run the auto channel function on the TV set and see what happens when the TV set tunes to only the signals it finds. Look for the local signals on a different channel.Linley
Re: Problem 2 - LCD tv reception Reply #5 – January 11, 2005, 05:44:13 pm Yahoo Message Number: 49188"As a GUESS, the CATV system has moved the local signals to another channel to keep the signal leakage under control." Yes! My gut instinct says that Linley nailed the problem. Cable companies frequently relocate local channels...so if Chris is looking for broadcast channel 2 on cable channel 2, he ain't gonna find it. It's there somewhere--it's just not where you expect it to be. Chris, you need to either get a channel reference card from your cable provider, or do what Steve suggested and let the TV find all the channels for you.Andy Baird
Re: Problem 2 - LCD tv reception Reply #6 – January 11, 2005, 08:22:19 pm Yahoo Message Number: 49198Quote "As a GUESS, the CATV system has moved the local signals to another channel to keep the signal leakage under control."Yes! My gut instinct says that Linley nailed the problem. Cable companies frequently relocate local channels...so if Chris is looking for broadcast channel 2 on cable channel 2... you need to either get a channel reference card from your cable provider, or do what Steve suggested and let the TV find all the channels for you. Thanks for the replies, but that's not it. I did run the auto channel select while on cable and so the broadcast channels are the ones that the cable company has relocated (i.e. I can tune in CBS on antenna channel 42 and it looks great, when I view it on cable channel 2, it's all snowy with static filled sound.)What's still puzzling me is why it happens ONLY on the LCD tv in the front entertainment center and not the regular tv in the back bedroom? When I get back to the RV this weekend, I'm going to hook up the regular tv to the cable connection in the entertainment center and see if it does the same thing, then that will at least isolate the problem to something in the front connection. Alternatively, if the regular tv does not get static, then it must be something wrong (or ultra sensitivity) with the LCD tv.Chris W. (BTW, I'm a she, hubby is Frank)
Re: Problem 2 - LCD tv reception Reply #7 – January 11, 2005, 08:37:33 pm Yahoo Message Number: 49201Another possibility is that the LCD TV needs to be changed from "CATV" to "TV" on its Menu. The channeling is different and needs to correspond.Steve T
Re: Problem 2 - LCD tv reception Reply #8 – January 11, 2005, 10:27:52 pm Yahoo Message Number: 49209Quote "As a GUESS, the CATV system has moved the local signals to another channel to keep the signal leakage under control." I am drawing from my memory (which isn't the best anymore) so I may be way out in left field on this. As I recall, many cable companies use a frequency for transmission of TV channels that is slightly different than the frequency used for "over the air" transmission. In other words, the cable companies shift the frequency for each channel up(?) a bit from "over the air" frequency. Why they do this, I don't know. I also think that this is done primarily (only?) for the VHF channels (channels 2 to 13)and that the cable and "over the air" frequencies for the VHF channels (above channel 13) are the same, or very close to being the same.To make TV sets that would would work with either cable or antenna (over the air) inputs, TV makers took one of two approaches:1. They incorporated into the TV set a tuner that had a bandwith broad enough to capture either the over the air or the cable signal. Then they added an "automatic frequency lock" that caused the tuner to lock (and work with) which ever frequency it received for a specific channel. If you had one of these sets and wanted to switch from "antenna" to "cable" you just unplugged the antenna and plugged in the cable and everything worked OK.2. They included in their "setup" menus an item that allowed you to specify whether the input was coming from over the air (antenna) or from cable. Selecting "cable" caused the TV set to change the frequency on which it expected to find each channel. At one time I had a chart that showed the channel frequencies for "on the air" and "cable" as provided by Cox Cable. Unfortunately I have lost it somewhere so can't provide you with the details of the frequencies. I suspect that the "cable frequencies" may differ from one cable vendor to the next, however, I am under the impression that there area FCC standards for the "cable shift."I do not have my 26.5 foot LD yet (Should get it by the end of February)so I cannot look at the LCD TV set to see what "adjustments" it has. As soon as I get my LD I will look at the TV and see how it works. Also, if I find my "cable channel frequencies" chart I will publish same. I believe, however, that the frequencies are FCC dictated or approved.Patientily waiting for my LD in "sunny San Diego" with rain soaked feet.Doug
Re: Problem 2 - LCD tv reception Reply #9 – January 11, 2005, 11:38:55 pm Yahoo Message Number: 49218QuoteAs I recall, many cable companies use a frequency for transmission ofTV channels that is slightly different than the frequency used for "over the air" transmission. Yes, they do. The over the air standard has a lot of unused spectrum and goes to a higher frequency than is economical to transmit on a CATV system. Channels 2-13 are pretty much on the same frequencies over the air as on CATV. But, over the air, channel 14 starts at 470 MHz and it runs upward channel by channel until channel 69 tops out at 806 MHz.On CATV channel 14 starts at 124 MHz and it goes linearly upward to channel 22 that tops out at 174 MHz. Channel 23 then starts just above channel 13 and starts a new sequence starting at 222 MHz. Each channel is higher than the last until the you reach whatever frequency the cable tops out at. The only cheat is that channels 95 through 99 are way down between 90 and 120 MHz (channels 95 to 98 are thus in the FM broadcast band).There are some slight variations in frequencies (of only a few kHz) that some CATV systems use to minimize various problems caused by putting so many signals on one cable.You can see a complete list at: http://www.arrl.org/tis/info/catv-ch.htmlMy best guess for Chris' case is that the CATV system doesn't have anything on the local channels' frequencies and the other set is picking up leakage from some source while the LCD one is shielded and shows nothing. When the TV stations are that close, it takes a really tight system to keep the off air signal from leaking in. Her experiment of moving the other set is a good one and should turn up something. But understand .... this is radio stuff. Radio stuff does its best to make fools out of professional radio people (like me). So, there is a 50:50 chance that it will be something completely different. (Its a lot like computer stuff!)Linley
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