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From: GregS on 3 Aug 2010 12:04
In article <8bo9bcFpu1U1(a)mid.individual.net>, news(a)analogconsultants.com wrote:
>Paul Keinanen wrote:
>> On Sun, 01 Aug 2010 14:14:29 -0700, Joerg <invalid(a)invalid.invalid>
>> wrote:
>>
>>> Just curious: Why is it that "modern" TV/VCR/DVD devices only allow
>>> auto-scan for DTV channels but no "add some later"? As most of us know
>>> DTV is unreliable, meaning sometimes channel 6-1 pixelates out,
>>> sometimes 58-2 is gone. So upon setup it will only catch the ones that
>>> are currently receivable, which in our case is never more than 80% of
>>> digital channels. Changes all the time.
>>
>> You seem to suffer from frequency selective fading, which is typical
>> in multipath conditions. This may eliminate the signal with sharp
>> notches (usually less than 1 MHz) and these notches are constantly
>> moving around the TV band when the propagation condition changes.
>> Thus, a few channels are suffering from multipath nulls during each
>> channel scan and hence, these are not stored.
>>
>> The 8VSB modulation used in ATSC is not known for robustness in
>> multipath situations. The help the situation, an equalizer is used at
>> the receiver that tries to compensate for the amplitude and phase
>> errors created by the RF path. The equalizer needs a known training
>> signal so that the equalizer parameters can be set up correctly. There
>> have been claims that with 5th (or was it 6th or 7th :-) generation
>> equalizers, the multipath performance is similar to COFDM DVB-T.
>>
>
>I think they failed to achieve that level of performance. Yesterday
>_all_ stations that carry evening news blue-screened. Meaning we could
>not watch the news. I guess this is called progess.

Lately, I frequently get one channel that stops. Sometimes if I go up a channel, then back,
it will work again.

I wish they would have presets on remotes. They do it with everything else.

I can't figure out how to have more than one cable box in the same room.
Maybe 3. Many watch TV on one channel, but thats crude. I need at least
two TV to watch. It happens all the time trying to switch back and forth channels.
When I asemble my home theater/entertainment room, I want at least
3 TV's.

Maybe this is easy. I know my brother has several boxes on a shelf for the TV's in the
sports bar.

greg

>
>> Apparently the 8VSB equalizer can somewhat track the slow RF-channel
>> parameter changes (starting the training session from previously known
>> good parameters), but during the initial channel scan, the equalizer
>> parameters are completely unknown for each new channel, the equalizer
>> is not capable of making any sense of some of the signals, even if the
>> amplitude is quite strong.
>>
>> My guess is that if you connect a spectrum analyzer to your antenna
>> signal, it will show a comb filter like spectrum.
>>
>
>No, it showed nice bricks for each station but the sets can't decode
>some of them.
>
>
>> Diversity receivers are available in DVB-T countries mainly for in-car
>> receivers, but do you have diversity receivers for ATSC ?
>>
>> Having two antenna towers at slightly different locations (at least
>> some wavelengths from each other) will have a different multipath
>> pattern. When one antenna and receiver drops out, the signal may be
>> good at the other antenna.
>>
>> Even simple RF summing of two antenna signals at different locations
>> may help avoiding deep nulls.
>>
>
>Sure, I could build 3-4 towers and provide a remote selector switch in
>the living room. That would really be technological progress :-)
>
From: GregS on 3 Aug 2010 12:09
In article <i39eht$nnq$1(a)usenet01.srv.cis.pitt.edu>, zekfrivo(a)zekfrivolous.com (GregS) wrote:
>In article <8bo9bcFpu1U1(a)mid.individual.net>, news(a)analogconsultants.com wrote:
>>Paul Keinanen wrote:
>>> On Sun, 01 Aug 2010 14:14:29 -0700, Joerg <invalid(a)invalid.invalid>
>>> wrote:
>>>
>>>> Just curious: Why is it that "modern" TV/VCR/DVD devices only allow
>>>> auto-scan for DTV channels but no "add some later"? As most of us know
>>>> DTV is unreliable, meaning sometimes channel 6-1 pixelates out,
>>>> sometimes 58-2 is gone. So upon setup it will only catch the ones that
>>>> are currently receivable, which in our case is never more than 80% of
>>>> digital channels. Changes all the time.
>>>
>>> You seem to suffer from frequency selective fading, which is typical
>>> in multipath conditions. This may eliminate the signal with sharp
>>> notches (usually less than 1 MHz) and these notches are constantly
>>> moving around the TV band when the propagation condition changes.
>>> Thus, a few channels are suffering from multipath nulls during each
>>> channel scan and hence, these are not stored.
>>>
>>> The 8VSB modulation used in ATSC is not known for robustness in
>>> multipath situations. The help the situation, an equalizer is used at
>>> the receiver that tries to compensate for the amplitude and phase
>>> errors created by the RF path. The equalizer needs a known training
>>> signal so that the equalizer parameters can be set up correctly. There
>>> have been claims that with 5th (or was it 6th or 7th :-) generation
>>> equalizers, the multipath performance is similar to COFDM DVB-T.
>>>
>>
>>I think they failed to achieve that level of performance. Yesterday
>>_all_ stations that carry evening news blue-screened. Meaning we could
>>not watch the news. I guess this is called progess.
>
>Lately, I frequently get one channel that stops. Sometimes if I go up a
> channel, then back,
>it will work again.
>
>I wish they would have presets on remotes. They do it with everything else.
>
>I can't figure out how to have more than one cable box in the same room.
>Maybe 3. Many watch TV on one channel, but thats crude. I need at least
>two TV to watch. It happens all the time trying to switch back and forth
> channels.
>When I asemble my home theater/entertainment room, I want at least
>3 TV's.
>
>Maybe this is easy. I know my brother has several boxes on a shelf for the TV's
> in the
>sports bar.

Another problem is turning off TV's in the same room or very large room.
The answer is, some remotes have both off and on buttons.

greg
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