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Old 01-17-2009, 08:32 AM   #1
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Question Why do channels fade away?

I have a new (2007) Bambi Safari.
It has the typical Winegard Batwing antenna.
I bought a new LG digital 19" flat panel TV.
I always use the 'power antenna booster'
(no reception at all without it!)
It gets great reception after a normal 'channel search'
and the picture quality of digital channels is superb.
However, I notice that after a few hours (or a day),
many channels have 'disappeared'.
A new search will solve the problem.
Why do channels shift and fade away.
The weather is not the issue.
(Of course, rotating the antenna will make
some channels better and some worse).
I can't imagine the TV is the problem.
Has anyone replaced these type antennas with a newer,
round, multi-directional type that may not even need to be elevated?
Do those types get better reception.... or more consistent?
Opinions?

Phantom
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Old 01-17-2009, 10:34 AM   #2
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My guess would be that the problem IS your new TV. If the search function fixes the problem, and then it comes back, it must be the TV. The search is a function of the TV, not the antenna or the booster.

I am using the old antenna that came on our '65 Caravel, and have had no problems with our 20" LCD HDTV. Once I do a search, nothing changes, no mater our location. If the antenna was the problem, we would probably be the first to have experience it.

Just my thoughts.
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Old 01-17-2009, 11:42 AM   #3
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What is the signal quality of the channels that disappear? Are they lower than the others that "stick around".
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Old 01-17-2009, 12:21 PM   #4
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Digital broadcast TV signals are less forgiving than analog. I find them harder to get and then to find the sweet spot, and then have to make a lot of adjustments for other channels. Such frustrations can lead to reading a book.

I have the Samsung factory installed HDTV. It works fine on cable, but I haven't stayed at a campground with HD cable yet—that'll take a while because they'll probably have to install new cable and much more expensive equipment to receive it.

We have gotten HDTV over the air in a few places. It's been fine once located, but there's not much we want to watch on broadcast TV except PBS. Every time we stay somewhere without cable, I learn again why broadcast TV has fewer and fewer viewers. I don't think the batwing antennas are specifically designed for HD and I suspect we will soon see on the market a replacement that is somewhat multidirectional. I hope satellite equipment and subscription prices go down (ha!) because that is the future. We have HD satellite at home and it's great, but expensive. Only if we traveled half the year or more would satellite TV in the trailer make sense to me.

Gene
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Old 01-17-2009, 12:29 PM   #5
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Frequency Drift??

Hi Phantom,
I'm not sure of the cause, but I think it's not the antenna and it may not be the TV. I'm guessing it may be some very small drift in the broadcast signal between the time you do a search and when you notice a degradation. Maybe this is tied to changes in temperature and/or humidity (Pacific NW weather here), but that might not jive with the changes you're seeing in a few hours or a day.

We use a couple of analog TV's in our home (i.e. stationary) with rabbit ears, so last year, I bought & installed 2 of the converter boxes (One was a Winegard and the other a Digital Stream -- they seem to be about equal in performance with a small edge to Digital Stream). When I first hooked them up, it was great. We had new, additional channels & very clear reception. About a month later we started noticing the loss of reception and it continued to degrade. Some of the 'new' channels disappeared. I was beginning to think the broadcasters were being cheap & cutting the power in the signal. Just before buying a more elaborate antenna arrangement, I tried doing the search process again, and it worked. Everything was back and working nicely. That was about a week ago, and it's still good.

Hopefully others more knowledgeable of electronics & radio waves can enlighten us on causes & possible resolutions.

Walt
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Old 01-17-2009, 01:30 PM   #6
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I am not particularly knowledgeable, but here's a shot at it—most radio signals are better at night, though digital TV operates on a different part of the spectrum which may be less affected by those type of changes. Weather can have some effects. When you are close to the edge of good reception, these things could make a difference. You can be farther from an analog transmitter and get good reception than from a digital transmitter.

Broadcasters have been broadcasting in both digital and analog and once digital is the only way, transmitters may be moved and that will make a difference. I think digital transmitters have in some cases been in less desirable locations and lower power, so there may be some improvement once analog is shut down. For some people, new antennas are necessary for digital because the length of the wave is different. It like the difference between VHF and UHF—UHF has much shorter waves and a UHF antenna has shorter parts than a VHF antenna; digital has shorter waves than UHF I think, but don't hold me to that.

Broadcast signals are not supposed to drift—the FCC has a lot of regulations about that. It does happen and some broadcasters get fined for it, but I doubt it happens very often. I would suspect, Walt, your problem was with the converter rather than the TV transmitter.

Gene
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Old 01-17-2009, 06:37 PM   #7
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Hi Gene,

That's a thoughtful response. I appreciate it and track with most of the points.

I did however, find the same issue with 2 converters from 2 manufacturers (Winegard and Digital Stream) which seems to reduce the odds of it being the converters.

Walt
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Old 01-17-2009, 06:56 PM   #8
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We bought a digital TV a about 13 months ago when camping down in Destin FL. We did notice that when viewing distant stations from either Panama City or Pennsicola in the digital mode, the ability to keep a good picture was also dependent upon time of day. I remember that the digital signals that would be weak in the daytime hours but strong at night. Not much different from the analog VHF signal pattern from the same stations. The big difference was the fact that a weak VHF analog signal would mean a fuzzy or snowy picture. In the digital world it means pixilation or complete loss of picture. You have little margin when aiming at those distant signals. A slight movement off will give you fits as the picture will pop in and out.

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Old 01-17-2009, 07:08 PM   #9
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Quote:
Originally Posted by CrawfordGene View Post
I think digital transmitters have in some cases been in less desirable locations and lower power, so there may be some improvement once analog is shut down. For some people, new antennas are necessary for digital because the length of the wave is different. It like the difference between VHF and UHF—UHF has much shorter waves and a UHF antenna has shorter parts than a VHF antenna; digital has shorter waves than UHF I think, but don't hold me to that.

Broadcast signals are not supposed to drift—the FCC has a lot of regulations about that. It does happen and some broadcasters get fined for it, but I doubt it happens very often. I would suspect, Walt, your problem was with the converter rather than the TV transmitter.

Gene
In addition Gene, due to the shorter wave length, the power requirements are greater. For those of you who deal with 2.4 gig (802.11b/g) WiFi, or 5 gig (802.11a), the power requirements to push that 5 gig signal are higher. I maintain the wireless facilities in the domed stadium here in St. Louis. I run my 2.4 gig radio at half power. The 5 gig has to run at full to get the same signal pattern using similar gain antennas.

One of the things that I just found out is that here in the St. Louis area, some of our local TV outlets will temporarily have a smaller signal pattern than the current VHS pattern. It's going to play havoc with some folks living out in the distant regions of the viewing area. Supposedly within 30 days the patterns will extend again. We have also been told that some of the existing UHF stations will be changing broadcast frequencies within the UHF band. So if you have already picking up the digital broadcasts of some of your UHF stations, on cut day that station might have to be rescanned due to it having to move to a new UHF frequency.

At this point I'm glad to have satellite although I did pick up two converter boxes from Dish Network for the cost of shipping only just in case I bail out or have some other issue with satellite.

Jack
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Old 01-17-2009, 08:52 PM   #10
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Most of us don't understand all that's happening here

Hi,

I hope this thread continues and we get some of the EE types to enlighten us (Cookbook kind of English please -- graphics help sometimes).

Walt
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Old 01-17-2009, 09:41 PM   #11
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Maybe somebody suggested this already, but here goes.

Phantom, take the new LG TV out of the Airstream and inside the house, if this is possible. If you have CATV in your house, connect the TV up to the Cable without the CATV converter. Have the TV scan for available channels. Let it stay in the house for a week or so and see if the channels "drift" away. If so, then the receiver in the TV is bad. We had a really bad experience with a low end digital TV a couple of months ago, so my money is on the TV, not the antenna (after a bunch of reading on the internet, I've decided that if you don't buy one of the high end models, expect problems sooner rather than later). If the problem is with the antenna, you might ask the local dealer where you bought the Airstream to help troubleshoot it. Is your Bambi still under warranty? The booster is most likely the issue there. Somebody here that knows more about the booster may be able to provide more info on that.

Hope this helps.

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Old 01-17-2009, 11:27 PM   #12
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Hi ALL,

To add to my frustration, about 15 minutes ago, in the middle of a show, channel 2 (ABC) cut out and we're seeing a 'No-Signal' indicator. I tried doing a new scan and channel 2 is now not even seen as a viable channel. To my knowledge, there's been no meaningful change in the weather (Temp, Humidity, or otherwise) in the last hour or so. My wife just now called to me to say channel 10 (KOPB) is now gone.

Does the FCC know this is happening?

Walt
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Old 01-18-2009, 08:01 AM   #13
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My guess it is the conditions in the ionosphere changes and the signal weakens or shifts slightly. The new tuners are much more senstive and have to be retuned. Just a guess.

or you can go with this. Ionospheric reflection coefficient for television signals
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Old 01-18-2009, 08:45 AM   #14
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Some of the digital signals are not running at "full" power, while the analog signals are still in place. Hopefully after the analogs are taken off the air the digitals will start transmitting at full power and most of these issues will be resolved. I have heard they are going to extend the deadline for another 30 days or so, for the braindead, confused folk.
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