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Naive question(s) about DTV

Started by Richard Owlett August 31, 2019
In the 60's I spent time as a BSEE student.
Took a course using _Signals, Systems and Communication_ , Lathi , 1965
A generation later I found comp.dsp and obtained a copy of
_Understanding Digital Signal Processing_ , Lyons, 2004

May I answers suitable for a bright high school student who reads 
eclectically {will account for what I've forgotten &/or never knew ;}.

I've a germ of an idea for a solution to a personal problem.
I suspect a basic understanding of a block diagram of how multiple 
signals modulate a single carrier to accomplish DTV would clarify my 
thoughts.

CAVEAT LECTOR:
avoided technical vocabulary for fear of causing confusion

TIA

On 31/08/2019 11:20, Richard Owlett wrote:
> In the 60's I spent time as a BSEE student. > Took a course using _Signals, Systems and Communication_ , Lathi , 1965 > A generation later I found comp.dsp and obtained a copy of > _Understanding Digital Signal Processing_ , Lyons, 2004 > > May I answers suitable for a bright high school student who reads > eclectically {will account for what I've forgotten &/or never knew ;}. > > I've a germ of an idea for a solution to a personal problem. > I suspect a basic understanding of a block diagram of how multiple > signals modulate a single carrier to accomplish DTV would clarify my > thoughts. > > CAVEAT LECTOR: > avoided technical vocabulary for fear of causing confusion > > TIA >
Parlez-vous Anglais?
Am 31.08.19 um 12:20 schrieb Richard Owlett:
> In the 60's I spent time as a BSEE student. > Took a course using _Signals, Systems and Communication_ , Lathi , 1965 > A generation later I found comp.dsp and obtained a copy of > _Understanding Digital Signal Processing_ , Lyons, 2004 > > May I answers suitable for a bright high school student who reads > eclectically {will account for what I've forgotten &/or never knew ;}. > > I've a germ of an idea for a solution to a personal problem. > I suspect a basic understanding of a block diagram of how multiple > signals modulate a single carrier to accomplish DTV would clarify my > thoughts. >
I translate it into modern English: "Could you please explain to me how DTV works?" Unfortunately, I have never heard of DTV. So somebody else has to take over, unless YOU explain to us what it is and what part you don't understand. Christian
On Sat, 31 Aug 2019 21:26:07 +0200, Christian Gollwitzer
<auriocus@gmx.de> wrote:

>Am 31.08.19 um 12:20 schrieb Richard Owlett: >> In the 60's I spent time as a BSEE student. >> Took a course using _Signals, Systems and Communication_ , Lathi , 1965 >> A generation later I found comp.dsp and obtained a copy of >> _Understanding Digital Signal Processing_ , Lyons, 2004 >> >> May I answers suitable for a bright high school student who reads >> eclectically {will account for what I've forgotten &/or never knew ;}. >> >> I've a germ of an idea for a solution to a personal problem. >> I suspect a basic understanding of a block diagram of how multiple >> signals modulate a single carrier to accomplish DTV would clarify my >> thoughts. >> > >I translate it into modern English: "Could you please explain to me how >DTV works?" > >Unfortunately, I have never heard of DTV. So somebody else has to take >over, unless YOU explain to us what it is and what part you don't >understand. > > Christian
Digital TeleVision ?
On Sat, 31 Aug 2019 05:20:23 -0500, Richard Owlett
<rowlett@cloud85.net> wrote:

>In the 60's I spent time as a BSEE student. >Took a course using _Signals, Systems and Communication_ , Lathi , 1965 >A generation later I found comp.dsp and obtained a copy of >_Understanding Digital Signal Processing_ , Lyons, 2004 > >May I answers suitable for a bright high school student who reads >eclectically {will account for what I've forgotten &/or never knew ;}. > >I've a germ of an idea for a solution to a personal problem. >I suspect a basic understanding of a block diagram of how multiple >signals modulate a single carrier to accomplish DTV would clarify my >thoughts. > >CAVEAT LECTOR: >avoided technical vocabulary for fear of causing confusion > >TIA >
I'm guessing you're asking about how OFDM works for DVB-T? 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. Also FWIW, DTV in the states is a kind of bizarro single-carrier single-sideband digital signal that the primary redeeming factor seems (to me) to be that spectrally it kind of resembles the analog signal that it replaced. Otherwise I don't know why anybody would decide to use it (and nobody else ever has, ever, for anything, afaik). Anyway, let us know if that's the right track.
On 08/31/2019 11:41 PM, Eric Jacobsen wrote:
> On Sat, 31 Aug 2019 05:20:23 -0500, Richard Owlett > <rowlett@cloud85.net> wrote: > >> In the 60's I spent time as a BSEE student. >> Took a course using _Signals, Systems and Communication_ , Lathi , 1965 >> A generation later I found comp.dsp and obtained a copy of >> _Understanding Digital Signal Processing_ , Lyons, 2004 >> >> May I answers suitable for a bright high school student who reads >> eclectically {will account for what I've forgotten &/or never knew ;}. >> >> I've a germ of an idea for a solution to a personal problem. >> I suspect a basic understanding of a block diagram of how multiple >> signals modulate a single carrier to accomplish DTV would clarify my >> thoughts. >> >> CAVEAT LECTOR: >> avoided technical vocabulary for fear of causing confusion >> >> TIA >> > > I'm guessing you're asking about how OFDM works for DVB-T? 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 articles were informative. Combined, they answered my questions. And the discussion of multipath interference may explain some weather related issues I've observed.
> > Also FWIW, DTV in the states is a kind of bizarro single-carrier > single-sideband digital signal that the primary redeeming factor seems > (to me) to be that spectrally it kind of resembles the analog signal > that it replaced.
I suspect that the occupied spectrum space remaining the same simplified the transition, at least politically. A station's assigned carrier frequency remained the same across the switch-over thus no new adjacent channel interference issues. IIRC the switch-over took a couple of years especially in rural areas and those served by a class of low power stations. Also there power advantages [https://en.wikipedia.org/wiki/8VSB#Power_saving_advantages].
> Otherwise I don't know why anybody would decide to > use it (and nobody else ever has, ever, for anything, afaik). > > Anyway, let us know if that's the right track.
The later was the answer needed. Thank you.
Richard Owlett  <rowlett@cloud85.net> wrote:

>On 08/31/2019 11:41 PM, Eric Jacobsen wrote:
>> Also FWIW, DTV in the states is a kind of bizarro single-carrier >> single-sideband digital signal that the primary redeeming factor seems >> (to me) to be that spectrally it kind of resembles the analog signal >> that it replaced.
>I suspect that the occupied spectrum space remaining the same simplified >the transition, at least politically. A station's assigned carrier >frequency remained the same across the switch-over thus no new adjacent >channel interference issues. IIRC the switch-over took a couple of years >especially in rural areas and those served by a class of low power >stations. Also there power advantages >[https://en.wikipedia.org/wiki/8VSB#Power_saving_advantages].
>> Otherwise I don't know why anybody would decide to >> use it (and nobody else ever has, ever, for anything, afaik). > >> Anyway, let us know if that's the right track.
>The later was the answer needed. Thank you.
The advantage of vestigal sideband is that the missing carrier frequency/phase information can be extracted from the vestigal sideband. In a pure single-sideband signal, that information is not there at all. But using this solution, as opposed to one of the many other possible solutions to the same problem, was probably driven by the spectral mask and the history. At the time, FCC liked the replacement signal design to resemble the legacy signal design, figuring that this preserves coexistence. (A policy they don't seem to follow more recently.) Steve
On Mon, 2 Sep 2019 21:34:29 +0000 (UTC), spope384@gmail.com (Steve
Pope) wrote:

>Richard Owlett <rowlett@cloud85.net> wrote: > >>On 08/31/2019 11:41 PM, Eric Jacobsen wrote: > >>> Also FWIW, DTV in the states is a kind of bizarro single-carrier >>> single-sideband digital signal that the primary redeeming factor seems >>> (to me) to be that spectrally it kind of resembles the analog signal >>> that it replaced. > >>I suspect that the occupied spectrum space remaining the same simplified >>the transition, at least politically. A station's assigned carrier >>frequency remained the same across the switch-over thus no new adjacent >>channel interference issues. IIRC the switch-over took a couple of years >>especially in rural areas and those served by a class of low power >>stations. Also there power advantages >>[https://en.wikipedia.org/wiki/8VSB#Power_saving_advantages]. > >>> Otherwise I don't know why anybody would decide to >>> use it (and nobody else ever has, ever, for anything, afaik). > >>> Anyway, let us know if that's the right track. > >>The later was the answer needed. Thank you. > >The advantage of vestigal sideband is that the missing carrier >frequency/phase information can be extracted from the vestigal sideband. >In a pure single-sideband signal, that information is not there at all. > >But using this solution, as opposed to one of the many other possible >solutions to the same problem, was probably driven by the spectral >mask and the history. At the time, FCC liked the replacement signal >design to resemble the legacy signal design, figuring that >this preserves coexistence. (A policy they don't seem to follow >more recently.) > >Steve
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 ?
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
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 =
> 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 =
> 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=
=2E
>=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 >=20