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Naive question(s) about DTV

Started by Richard Owlett August 31, 2019
On Tuesday, September 3, 2019 at 8:42:05 AM UTC-4, Richard Owlett wrote:
> On 09/03/2019 07:32 AM, Richard Owlett wrote: > > On 09/01/2019 05:58 AM, Richard Owlett wrote: > >> On 08/31/2019 11:41 PM, Eric Jacobsen wrote: > >>> On Sat, 31 Aug 2019 05:20:23 -0500, Richard Owlett > > [snip] > >>> > >>> I'm guessing you're asking about how OFDM works for DVB-T?=C2=A0=C2=
=A0 These
> >>> days a lot of other systems also use various flavors of OFDM, but it > >>> is one of the harder modulations to get your head around. > >> > >> I didn't recognize those acronyms but the respective Wikipedia=20 > >> articles were informative. Combined, they answered my questions. And=
=20
> >> the discussion of multipath interference may explain some weather=20 > >> related issues I've observed. > >> > >=20 > > Due to circumstances I must use an indoor antenna and local topography=
=20
> > puts it not far above average terrain. In days of analog TV I had=20 > > impressive ghosts ;}! > >=20 > > The weather related issue I referred to was how I have to place/orient=
=20
> > the antenna which varies with: > > =C2=A0 1. incoming strong frontal system {PS this is Tornado Alley ;} > > =C2=A0 2. season > >=20 > > Two Wikipedia articles I read mentioned improvements in receiver design=
.
> >=20 > > https://en.wikipedia.org/wiki/8VSB > >> Early 8VSB DTV (digital television) receivers often had difficulty > >> receiving a signal in urban environments. Newer 8VSB receivers, howeve=
r,
> >> are better at dealing with multipath, ... > >=20 > > https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexin=
g
> >> However, newer 8VSB receivers are far better at dealing with multipath=
,
> >> hence the difference in performance may diminish with advances in=20 > >> equalizer design.[citation needed] ^^^^^^^^^^^^^^=
^^ {moved carets}
> >=20 > > My current set was purchased within a couple of year of the transition.=
=20
> > How likely is it that I would see a worthwhile improvement? I don't hav=
e=20
> > room for=C2=A0 screen much larger than I currently have. I suspect that=
=20
> > implies a less expensive set with perhaps poorer performance. > >=20 > > Comments? > > TIA > >=20 > >=20 > >=20 > >=20 > >=20 > >=20 > >=20 > >
you may want to buy a low cost USB-PC based type RF spectrum analyzer and = observe the signals. Dynamic multi-path is the primary impairment. And th= e design of the adaptive equalizer in your particular receiver is critical = to overcoming that impairment. =20 Also in the US other acronym search terms for DTV is ATSC and 8VSB. Mark
On Tue, 3 Sep 2019 07:32:03 -0500, Richard Owlett
<rowlett@cloud85.net> wrote:

>On 09/01/2019 05:58 AM, Richard Owlett wrote: >> On 08/31/2019 11:41 PM, Eric Jacobsen wrote: >>> On Sat, 31 Aug 2019 05:20:23 -0500, Richard Owlett >[snip] >>> >>> I'm guessing you're asking about how OFDM works for DVB-T?=C2=A0=C2=A0= > These >>> days a lot of other systems also use various flavors of OFDM, but it >>> is one of the harder modulations to get your head around. >>=20 >> I didn't recognize those acronyms but the respective Wikipedia articles= >=20 >> were informative. Combined, they answered my questions. And the=20 >> discussion of multipath interference may explain some weather related=20 >> issues I've observed. >>=20 > >Due to circumstances I must use an indoor antenna and local topography=20 >puts it not far above average terrain. In days of analog TV I had=20 >impressive ghosts ;}! > >The weather related issue I referred to was how I have to place/orient=20 >the antenna which varies with: > 1. incoming strong frontal system {PS this is Tornado Alley ;} > 2. season > >Two Wikipedia articles I read mentioned improvements in receiver design. > >https://en.wikipedia.org/wiki/8VSB >> Early 8VSB DTV (digital television) receivers often had difficulty >> receiving a signal in urban environments. Newer 8VSB receivers, however= >, >> are better at dealing with multipath, ... > >https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing >> However, newer 8VSB receivers are far better at dealing with multipath,= > >> hence the difference in performance may diminish with advances in equal= >izer >> design.[citation needed] ^^^^^^^^^^^^^^^^^^ > >My current set was purchased within a couple of year of the transition.=20 >How likely is it that I would see a worthwhile improvement? I don't have = > >room for screen much larger than I currently have. I suspect that=20 >implies a less expensive set with perhaps poorer performance. > >Comments? >TIA
The "improved equalizer design" is just that they can afford to make a more complex equalizer with more taps since gates on silicon have gotten a lot cheaper over the years. So they throw complexity at it, and it does perform better and doesn't really add any significant cost or power consumption. I think you're right that TVs are pretty cheap these days and it's likely that the performance will be better than what you currently have in that particular characteristic (and maybe some others!). If you have decent internet and a WiFi access point, get a smart TV and you can get content over the internet, too, and not be stuck with the over-the-air stuff. BTW, I found out recently that there are still some TV stations around broadcasting analog NTSC signals. I've no idea what's up with that.
On 09/04/2019 07:26 PM, Eric Jacobsen wrote:
> On Tue, 3 Sep 2019 07:32:03 -0500, Richard Owlett > <rowlett@cloud85.net> wrote: > [snip] >> Due to circumstances I must use an indoor antenna and local topography >> puts it not far above average terrain. In days of analog TV I had >> impressive ghosts ;}! >> >> The weather related issue I referred to was how I have to place/orient >> the antenna which varies with: >> 1. incoming strong frontal system {PS this is Tornado Alley ;} >> 2. season >> >> Two Wikipedia articles I read mentioned improvements in receiver design. >> >> https://en.wikipedia.org/wiki/8VSB >>> Early 8VSB DTV (digital television) receivers often had difficulty >>> receiving a signal in urban environments. Newer 8VSB receivers, >>> however, howeverare better at dealing with multipath, ... >> >> https://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexing >>> However, newer 8VSB receivers are far better at dealing with multipath, >>> hence the difference in performance may diminish with advances in >>> equalizer design.[citation needed] >> >> My current set was purchased within a couple of years of the transition. >> How likely is it that I would see a worthwhile improvement? I don't have >> room for screen much larger than I currently have. I suspect that >> implies a less expensive set with perhaps poorer performance. >> >> Comments? >> TIA > > The "improved equalizer design" is just that they can afford to make a > more complex equalizer with more taps since gates on silicon have > gotten a lot cheaper over the years. So they throw complexity at it, > and it does perform better and doesn't really add any significant cost > or power consumption.
Evidently, according to Wikipedia, Moore's Law is aging gracefully.
> > I think you're right that TVs are pretty cheap these days and it's > likely that the performance will be better than what you currently > have in that particular characteristic (and maybe some others!).
I don't expect to see explicit mention of "improved multi-path rejection" in promotional material aimed at general population. What should I look for? Or just look for other attractive features and take my chances ;/
> If > you have decent internet and a WiFi access point, get a smart TV and > you can get content over the internet, too, and not be stuck with the > over-the-air stuff.
ROFL I quit dial-up only because my ISP ended that service. They only had a half dozen clients using it <GRIN> I'm quite happy with my current 2GB data cap service.
> > BTW, I found out recently that there are still some TV stations around > broadcasting analog NTSC signals. I've no idea what's up with that.
IIRC they are likely community owned systems serving area where commercial TV was not economically viable.
On 09/05/2019 06:13 AM, Richard Owlett wrote:
> [snip] >> >> The "improved equalizer design" is just that they can afford to make a=
>> more complex equalizer with more taps since gates on silicon have >> gotten a lot cheaper over the years.=C2=A0=C2=A0 So they throw complex=
ity at it,
>> and it does perform better and doesn't really add any significant cost=
>> or power consumption. >=20 > Evidently, according to Wikipedia, Moore's Law is aging gracefully. >=20 >> >> I think you're right that TVs are pretty cheap these days and it's >> likely that the performance will be better than what you currently >> have in that particular characteristic (and maybe some others!). >=20 > I don't expect to see explicit mention of "improved multi-path=20 > rejection" in promotional material aimed at general population. > What should I look for? Or just look for other attractive features and =
> take my chances ;/
Turns out the "attractive feature" will be " *small* enough" to be=20 comfortably viewed. I have a small house built ~1890 on what was then=20 "the wrong side of the tracks". My recliner is <10 ft from TV ;} Target, at least, is apparently discontinuing small enough TVs.
>=20 >=20 >> If >> you have decent internet and a WiFi access point, get a smart TV and >> you can get content over the internet, too, and not be stuck with the >> over-the-air stuff. >=20 > ROFL > I quit dial-up only because my ISP ended that service. They only had a =
> half dozen clients using it <GRIN> I'm quite happy with my current 2GB =
> data cap service. >=20 >=20 >> >> BTW, I found out recently that there are still some TV stations around=
>> broadcasting analog NTSC signals.=C2=A0=C2=A0 I've no idea what's up w=
ith that.
>=20 > IIRC they are likely community owned systems serving area where=20 > commercial TV was not economically viable.
theman@ericjacobsen.org (Eric Jacobsen) writes:
> [...] > BTW, I found out recently that there are still some TV stations around > broadcasting analog NTSC signals. I've no idea what's up with that.
Yeah, that is surprising. I thought the transition out for NTCS was over a decade ago. These are legitimate registered stations? -- Randy Yates, DSP/Embedded Firmware Developer Digital Signal Labs http://www.digitalsignallabs.com
On 09/04/2019 07:26 PM, Eric Jacobsen wrote:
> [snip] >> >> Due to circumstances I must use an indoor antenna and local topography >> puts it not far above average terrain. In days of analog TV I had >> impressive ghosts ;}! >> >> The weather related issue I referred to was how I have to place/orient >> the antenna which varies with: >> 1. incoming strong frontal system {PS this is Tornado Alley ;} >> 2. season >> >> Two Wikipedia articles I read mentioned improvements in receiver design. >>[snip] > > The "improved equalizer design" is just that they can afford to make a > more complex equalizer with more taps since gates on silicon have > gotten a lot cheaper over the years. So they throw complexity at it, > and it does perform better and doesn't really add any significant cost > or power consumption. > > I think you're right that TVs are pretty cheap these days and it's > likely that the performance will be better than what you currently > have in that particular characteristic (and maybe some others!). If > you have decent internet and a WiFi access point, get a smart TV and > you can get content over the internet, too, and not be stuck with the > over-the-air stuff.
Turns out my existing set is newer than I thought - only 4 years old. Bought a new one anyway. Performance seems pretty much the same. Due to space restrictions it was the smallest offered, therefore on the low end of the price range. I'll have to figure out a practical method of adjusting both antenna elevation and orientation (optimal values of *BOTH* have been demonstrated to vary with conditions). As I live in Tornado Alley, I'm not considering an outdoor antenna. Mark had written:
> you may want to buy a low cost USB-PC based type RF spectrum analyzer > and observe the signals. Dynamic multi-path is the primary impairment.
I can see the spectrum analyzer as a tool for observing, on a per channel basis, the signal _strength_ as a function of antenna elevation/orientation. I don't understand what multi-path artifacts I might be able to observe.
> And the design of the adaptive equalizer in your particular receiver is > critical to overcoming that impairment.
Understood. But I have no control of that. Now if I had the work-space I had 50 years ago, who knows what I might attempt? When I did an internet search I found more links about using a spectrum analyzer than that useful information on where to obtain one and relative cost/performance trade-offs. Suggestions? [I avoid Ebay and Amazon with a passion ;] TIA
On Monday, September 2, 2019 at 10:39:51 PM UTC-7, boB wrote:

(snip regarding analog television vestigial sideband modulation)

> Very interesting point ! I wonder if they make use of that extra bit > of information ? I would think that if they needed to use the > vestigial part that the main sideband would be messed up enough that > it would be unusable ?
> Never even asked why that sideband was there at all before... Maybe > because it's easier than filtering or cancelling out all the way ?
In the case of NTSC VSB, the lower sideband is filtered out with a specific frequency range. The result, then, of demodulating the signal as a normal AM signal is that the frequency response isn't flat. The lower sideband is cut off at about (I don't know the exact shape) 1MHz. The result is that the demodulated signal is reduced by half past 1MHz. The IF amplifiers, then, are designed to compensate for this. Getting the frequency response in audio may seem more obvious, but it is still considered important in video.