DTV reception is much more difficult than analog

[Guest]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

Alan wrote:
> In article <1112295350.890069.113640@l41g2000cwc.googlegroups.com> "inkyblacks@yahoo.com" <inkyblacks@yahoo.com> writes:
>
>>Yesterday I tried one more position for my indoor antenna and found
>>that by raising it by just one more foot, I was for the first time able
>>to get all local digital channels in the middle of the day without
>>moving the position of the antenna. Who could imagine that one lousy
>>foot would make such a big difference!
>
>
> Anyone who has ever looked at the issues of indoor TV antennas.
>
>
>
>> So it has taken me 10 months to
>>find the sweet spot in my apartment for my antenna, and I have to use a
>>specific indoor antenna (Silver Sensor) with an antenna amp (Zenith
>>indoor amp) to get the system to work.
>
>
> Or, an outdoor antenna. As many of us have explained, there are reflections
> of the signals indoors, blockages by metal in the walls, diffraction around the
> edges (such as through windows).
>
> There will be dead spots.
>
> The dead spots will vary as people move around in the room
>
>
>
>>How are old ladies going to deal with over-the-air digital TV?
>
>
> By putting the antenna outside, where it belongs.
>
>
>> The
>>other thing I don't like is the labeling of channels like 9.1 and 9.2.
>>This scheme is too complex for most people. Unless you are technically
>>inclined and have patience, or are lucky enough to be able to have a
>>good outdoor antenna, I think OTA digital is too much work and
>>complexity for the elderly and for women.
>
>
> Oh, you think the elderly and women are incapable? What a snot you
> are!
>
>
>
>>Better receiver chips would help.
>
>
> No, they wouldn't. If the signal is not present in a spot, it does't
> matter what receiver you use.
>
>
> Alan

Dead spots in the room are rare with COFDM. Maybe because with COFDM in
a room you would use an omni antenna where with 8-VSB to avoid the
multipath problem with to many signals bouncing around that room you
would use a directional antenna.

The omni with COFDM welcomes the multipath signal no matter where it is
bouncing from and is capable of adding these signals together for a
stronger signal whereas the directional with 8-VSB is trying to
specifically avoid these other signals and just concentrate on the main
or strongest signal.

So don't blame to much on dead spots, it may be the directional antenna
that is not aimed at all the signals at once.

Bob Miller

 

[Guest]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

inkyblacks@yahoo.com wrote:
> Alan,
>
> It is often not a black and white issue of signal or no signal. The LG 5th chip receiver claims to be able to display signals at one fourth
> the signal strength of previous designs. In the apartment where it was tested, they picked up stations that they could not pick up before and
> picked up all signals detected with a scope. There may be situations where even the best receiver will not help, but certainly if reports
> from Bob Miller and Sinclair are true about the LG design, it is a big boost to indoor reception in America.
>
> IB
>

Yes and as we stood there with the designers of the 5th gen chip from LG
they gave due credit to COFDM as the source of their inspiration.

Photos of Korean engineers here.
http/public.fotki.com/robmx/5th_generation_test/

Bob Miller

 

[Alan]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

In article <GM33e.77$N13.66@newsread3.news.pas.earthlink.net> Bob Miller <robmx@earthlink.net> writes:
>Alan wrote:
>> No, they wouldn't. If the signal is not present in a spot, it does't
>> matter what receiver you use.

>Dead spots in the room are rare with COFDM. Maybe because with COFDM in
>a room you would use an omni antenna where with 8-VSB to avoid the
>multipath problem with to many signals bouncing around that room you
>would use a directional antenna.

No, this is nonsense. The symbol rate of 8vsb is not that high. Multipath
within the room will not be an issue for intersymbol interference.


>The omni with COFDM welcomes the multipath signal no matter where it is
>bouncing from and is capable of adding these signals together for a
>stronger signal whereas the directional with 8-VSB is trying to
>specifically avoid these other signals and just concentrate on the main
>or strongest signal.

The problem, twit, is that the signals also CANCEL when they combine with
the strong reflections indoors. When the signals CANCEL, it doesn't matter
if you are using 8VSB, COFDM, NTSC, or something else. No signal is no signal.


>So don't blame to much on dead spots, it may be the directional antenna
>that is not aimed at all the signals at once.


As for indoor aerials (antennas) with the U.K. Freeview system:

http/www.freeview.co.uk/faqs/aerialsandreception.html

I quote from there:

A small number of households may be able to use a set top aerial.
This only applies if you live in a coverage area close to a
transmitter, but reception would still be unreliable and so we
strongly recommend that you use a roof or loft aerial for good
reception.


So, the folks who use COFDM say it doesn't have this magical ability
to work with indoor antennas.


Alan

 

[Guest]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

Alan wrote:
> In article <GM33e.77$N13.66@newsread3.news.pas.earthlink.net> Bob Miller <robmx@earthlink.net> writes:
>
>>Alan wrote:
>>
>>> No, they wouldn't. If the signal is not present in a spot, it does't matter what receiver you use.
>
>
>>Dead spots in the room are rare with COFDM. Maybe because with COFDM in a room you would use an omni antenna where with 8-VSB to avoid the
>>multipath problem with to many signals bouncing around that room you would use a directional antenna.
>
>
> No, this is nonsense. The symbol rate of 8vsb is not that high. Multipath within the room will not be an issue for intersymbol interference.
>
The fact is that with 8-VSB with indoor directional antennas it is easy
to kill reception in a room by simply walking around or by a person
simply taking a particular position. If the signal interference creates
nulls that 8-VSB can't handle or if it is simply multipath that fact
remains that COFDM does not have this problem at the same power levels
or even much lower in our experience.
>
>
>>The omni with COFDM welcomes the multipath signal no matter where it is bouncing from and is capable of adding these signals together for a
>>stronger signal whereas the directional with 8-VSB is trying to specifically avoid these other signals and just concentrate on the main
>>or strongest signal.
>
>
> The problem, twit, is that the signals also CANCEL when they combine with the strong reflections indoors. When the signals CANCEL, it doesn't matter
> if you are using 8VSB, COFDM, NTSC, or something else. No signal is no signal.
>
Is your only argument name calling? Signals cancel and no signal is no
signal, understood. But COFDM working in a room with an omni antenna
where 8-VSB fails using a directional antenna while the 8-VSB signal is
coming from a near transmitter at 800,000 Watts and COFDM is coming from
a far antenna with 1000 Watts indicates that COFDM does not seem to
suffer from the number of nulls you suggest affect 8-VSB. Since there
should be the same number of nulls for both signals the facts that I
know suggest that it is NOT nulls but multipath that is killing 8-VSB
even with 5th gen prototype LG receiver this was true. It could not hold
a candle to a 1999 COFDM receiver for indoor reception.
>
>
>>So don't blame to much on dead spots, it may be the directional antenna that is not aimed at all the signals at once.
>
>
>
> As for indoor aerials (antennas) with the U.K. Freeview system:
>
> http/www.freeview.co.uk/faqs/aerialsandreception.html
>
> I quote from there:
>
> A small number of households may be able to use a set top aerial. This only applies if you live in a coverage area close to a
> transmitter, but reception would still be unreliable and so we strongly recommend that you use a roof or loft aerial for good
> reception.
>
>
> So, the folks who use COFDM say it doesn't have this magical ability to work with indoor antennas.

The folks who are using the 2K version of COFDM in the UK at average
power levels of 3.7 kW are saying this. BTW some folks in the UK under
these remarkable conditions are reporting perfect reception with indoor
antennas at 25 miles of these obscenely low transmitter powers.

And then there is the reality that in the UK using these absurd low
power levels 500,000 receivers will be purchased in April. They probably
work pretty good with just about any kind of antenna as reported by
friends there.

Bob Miller
>
>
> Alan

 

[Guest]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

inkyblacks@yahoo.com wrote:
> Bob,
>
> Nice pictures Bob!
>
> Alan,
>
> You need to call your mother and ask her to give you a lesson in
> manners.
>
> IB
>
The gentleman called Richard in the photos is Richard Bogner of Bogner
antenna fame. He built about 50% of the antennas broadcasters used over
the years AFAIK. Built antennas for the Apollo manned missions to the
Moon and was involved in the antennas that were used in the early
warning DEW line across northern Canada. He is the one holding the
winning loop antenna. A COFDM convert who had been in the TV antenna
business since day one.

Meric Adriansen in the photos worked for ABC testing COFDM for a number
of years. ABC was a big fan of COFDM before the Congressional
intimidation games.

Bob Miller

 

[Guest]

Archived from groups: alt.tv.tech.hdtv,alt.video.digital-tv (More info?)

inkyblacks@yahoo.com (inkyblacks@yahoo.com) wrote in alt.tv.tech.hdtv:
> It is often not a black and white issue of signal or no signal. The LG
> 5th chip receiver claims to be able to display signals at one fourth
> the signal strength of previous designs.

That claim is bogus. Raw signal strength has little effect on reception
of digital TV signals. The important number is carrier-to-noise
ratio (C/N). As long as it is above the 19dB threshold required for ATSC,
you get a picture. If it is less, you don't get a picture. Dropouts are
caused by the signal moving above and below the threshold.

I can remove my pre-amp (26dB) and add a 12dB attenuator and still receive
every station I get now. That's 38dB of raw signal strength attenuation,
but the C/N change is only about 3-6dB for me. Since all of my stations
are at least 22dB (and some as high as 30dB) C/N right now, I don't lose
the picture on any of them.

But, you want as much headroom as possible on C/N, so I use the pre-amp.
The problem with an indoor antenna is that there can easily be 50-70dB
of attenuation on the raw signal, and that will likely result in a drop
of C/N of 10-15dB. Theoretical maximum headroom on C/N for ATSC is
something like 20dB, and it is very difficult to achieve that (if you are
close enough to the antenna to get a lot of raw signal, you run into
problems with the design of the receiver and end up with overload, which
lowers C/N). My 11dB headroom on a couple of channels is in the "awesome"
category.

To put some of this in perspective, NTSC requires about 45dB C/N to achieve
a quality picture, and getting more than 10dB of headroom is virtually
impossible. Typicaly headroom on C/N for FM radio is less than 6dB.

--
Jeff Rife |
| http/www.nabs.net/Cartoons/RhymesWithOrange/MailerDaemon.gif

 

[Richard]

Archived from groups: alt.tv.tech.hdtv (More info?)

"Charles Tomaras" <tomaras@tomaras.com> wrote:


>It's funny how everyone thinks that straight shots across water should make
>for great reception but my professional experience as a sound mixer working
>with wireless microphones over the years has proven otherwise. It's
>sometimes very nice to have some concrete and buildings around for stuff to
>bounce off of. For being 100% wet, water sure can soak up RF!
>

Actually Charles, being NEAR the shores of a large body of water
allows an HF communication advantage. Just ask anyone involved in
amateur radio and they will tell you that it is extremely hard to
compete with anyone on or near the coast.

While it is true that reflections may help VHF or UHF, they may also
hurt. One final point, a phenomenon called ducting, which occurs over
water, has allowed UHF communication over a distance as great as 2500
kilometers.

Richard

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

"Richard" <rstaples312@yahoo.com> wrote in message
news:7pm751hon553p524o78adi8ok6np3m02lt@4ax.com...
> "Charles Tomaras" <tomaras@tomaras.com> wrote:
>
>
>>It's funny how everyone thinks that straight shots across water should
>>make
>>for great reception but my professional experience as a sound mixer
>>working
>>with wireless microphones over the years has proven otherwise. It's
>>sometimes very nice to have some concrete and buildings around for stuff
>>to
>>bounce off of. For being 100% wet, water sure can soak up RF!
>>
>
> Actually Charles, being NEAR the shores of a large body of water
> allows an HF communication advantage. Just ask anyone involved in
> amateur radio and they will tell you that it is extremely hard to
> compete with anyone on or near the coast.
>
> While it is true that reflections may help VHF or UHF, they may also
> hurt. One final point, a phenomenon called ducting, which occurs over
> water, has allowed UHF communication over a distance as great as 2500
> kilometers.
>
> Richard


My "water" experiences stem more from working professionally with 100mw
transmitters for body worn wireless microphones. Anytime someone is on the
water in a small boat etc...it's very tough to have dropout free reception.
I use diversity RF receivers that are pretty smart when dealing with
reflections and the such...it's when you only have one tiny line of site
chance on the water that ANYTHING can interfere.

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

On Wed, 6 Apr 2005, Richard wrote:
> "Charles Tomaras" <tomaras@tomaras.com> wrote:
> >It's funny how everyone thinks that straight shots across water should make
> >for great reception but my professional experience as a sound mixer working
> >with wireless microphones over the years has proven otherwise. It's
> >sometimes very nice to have some concrete and buildings around for stuff to
> >bounce off of. For being 100% wet, water sure can soak up RF!
>
> Actually Charles, being NEAR the shores of a large body of water
> allows an HF communication advantage. Just ask anyone involved in
> amateur radio and they will tell you that it is extremely hard to
> compete with anyone on or near the coast.
>
> While it is true that reflections may help VHF or UHF, they may also
> hurt. One final point, a phenomenon called ducting, which occurs over
> water, has allowed UHF communication over a distance as great as 2500
> kilometers.

Ducting can occur for TV signals too. About 10 years ago, I was able to see a
very snowy picture from WCCV in Arecibo, PR, here in Los Angeles. That's
probably not going to be possible with DTV however (unless signal strength is
very good).

 

[Guest]

Archived from groups: alt.tv.tech.hdtv (More info?)

On Wed, 6 Apr 2005, Charles Tomaras wrote:
> "Richard" <rstaples312@yahoo.com> wrote in message
> news:7pm751hon553p524o78adi8ok6np3m02lt@4ax.com...
> > "Charles Tomaras" <tomaras@tomaras.com> wrote:
> >>It's funny how everyone thinks that straight shots across water should make
> >>for great reception but my professional experience as a sound mixer working
> >>with wireless microphones over the years has proven otherwise. It's
> >>sometimes very nice to have some concrete and buildings around for stuff to
> >>bounce off of. For being 100% wet, water sure can soak up RF!
> >>
> >
> > Actually Charles, being NEAR the shores of a large body of water allows an
> > HF communication advantage. Just ask anyone involved in amateur radio and
> > they will tell you that it is extremely hard to compete with anyone on or
> > near the coast.
> >
> > While it is true that reflections may help VHF or UHF, they may also hurt.
> > One final point, a phenomenon called ducting, which occurs over water, has
> > allowed UHF communication over a distance as great as 2500 kilometers.
> >
> > Richard
>
>
> My "water" experiences stem more from working professionally with 100mw
> transmitters for body worn wireless microphones. Anytime someone is on the
> water in a small boat etc...it's very tough to have dropout free reception. I
> use diversity RF receivers that are pretty smart when dealing with
> reflections and the such...it's when you only have one tiny line of site
> chance on the water that ANYTHING can interfere.

Very low power and lack of grounding could contribute to your problem. This
isn't a problem for non-part-15 devices.