How does digital TV broadcast prevent ghosting effects?

[Joerg]

Joerg, ATSC works fine, the problem is with your setup.

No, the problem is the mandate. Fact is, analog works better.

Here are some ways you can fix it:

1. Exchange your TV for a model with a more robust ATSC tuner.

Nope. Just bought a brand new one. Supposedly has a pretty good tuner.
Besides, I've heard from others who plunked down north of $2k that it
ain't much different for them either.

2. Re-aim your antenna for best ATSC reception.

That I might have to do, sacrifice some channels so that others can be
received better. This will mean a net reduction in TV content but fine
with me.

3. Replace your antenna with something with better directionality and F/B
ratio.

Seriously, you can't possibly get a better one except by building your
own. Which, of course, is an option but TV ain't that important.

4. Accept that living in the boonies has costs and benefits, and one of
the costs is paying for cable or satellite TV.

Fact is: Analog TV and a $300 set worked just fine. Then came a mandate
from above that we all "will like and thus have to eat" DTV. Now digital
TV and a $750 set does not work reliably. That rationale is pretty
simple to me and others out here.

5. Download your TV shows from the internet using BitTorrent.

That's what many out here will probably start doing. Except the folks on
sat downlinks, they'll be out of the game and they'll probably
concentrate more on DVD renting. Anyhow, if this is the trend and I were
a TV station employee I'd be a bit concerned about job security. Usually
goes like this: Less viewers -> less ad revenue -> pink slips.

Of course if you're not willing to make any changes, you're not going to
solve the problem.

I am willing to make changes as long as they are reasonable. Signing up
for some $40-50/month cable deal isn't IMHO.

 

[Jeff Liebermann]

And that one could be huge. There is stuff that voters forget, and then
there is stuff they don't forget. And you can be sure that this will be
mined in the election after that one, along the lines of "these are the
guys who dunnit".

Ah, but the congress critters are not stupid. They're using our tax
dollars to give away rebate coupons for DTA (digital to analog) TV
converter boxes:
<http://www.ntia.doc.gov/dtvcoupon/>
Again, note that the date was safely set to AFTER the Nov 2008
election, where the likely culprits would be safely out of office.

I've tried those tricks. Thing is, reflections (bounces) seem to happen
multiple times. Meaning a back reflection comes bouncing back from the
front again. That's why it gets really bad when a 747 freighter glides
in, probably because it's a nearly perfect reflector.

Grinding....
10*10^-6 seconds * 3*10^8 meters/sec = 3km
path difference. I'll guess that the stations are about 10 miles or
16km distant. Grinding the trig, that puts the 747 flying at 5km
altitude at 8km range (midpoint). That's a bit high for a 747 on
approach.

A more reasonable 747 approach altitude might be perhaps 300 meters,
which would yield a single bounce reflected path length difference of
0.18km or:
0.18km / 3*10^8 m/sec = 0.6 microseconds.

If there are multiple bounces along the path, it will be roughly
multiples of this path delay. 10 microseconds would be about 12 to 15
bounces, which methinks is improbable. Have you looked at the
composite video signal coming out of the TV? With a decent trigger,
it should show the ghosts.

Back to the original question, there are apparently various patents
for methods of TV ghost elimination for both analog and digital TV. I
don't have any experience with these so I can't seperate reality from
science fiction. Looks like an adaptive equalizer will work work
HDTV. From what I've skimmed, most equalizers are more complexicated
than what I could throw together in an afternoon. This one looks
interesting:
<http://www.google.com/patents?id=uIomAAAAEBAJ&dq>
See other patents in list of citations or searching for "television
ghost"

 

[Joerg]

Ah, but the congress critters are not stupid. They're using our tax
dollars to give away rebate coupons for DTA (digital to analog) TV
converter boxes:
<http://www.ntia.doc.gov/dtvcoupon/>
Again, note that the date was safely set to AFTER the Nov 2008
election, where the likely culprits would be safely out of office.



Grinding....
10*10^-6 seconds * 3*10^8 meters/sec = 3km
path difference. I'll guess that the stations are about 10 miles or
16km distant. Grinding the trig, that puts the 747 flying at 5km
altitude at 8km range (midpoint). That's a bit high for a 747 on
approach.

A more reasonable 747 approach altitude might be perhaps 300 meters,
which would yield a single bounce reflected path length difference of
0.18km or:
0.18km / 3*10^8 m/sec = 0.6 microseconds.

It's a bit different. Echoes coming off slopes far behind us, hitting
the 747 at 800ft or so 1-3 miles out front and then that bounces back
into the antenna together with the direct signal.

If there are multiple bounces along the path, it will be roughly
multiples of this path delay. 10 microseconds would be about 12 to 15
bounces, which methinks is improbable. Have you looked at the
composite video signal coming out of the TV? With a decent trigger,
it should show the ghosts.

I've looked at the cerration pulses because they are nice and crisp
under normal reception condition. And oh boy do they squirm when that
747 glides in. Sometimes I thought I could actually guess the approach
speed sitting there at the scope.

Back to the original question, there are apparently various patents
for methods of TV ghost elimination for both analog and digital TV. I
don't have any experience with these so I can't seperate reality from
science fiction. Looks like an adaptive equalizer will work work
HDTV. From what I've skimmed, most equalizers are more complexicated
than what I could throw together in an afternoon. This one looks
interesting:
<http://www.google.com/patents?id=uIomAAAAEBAJ&dq>
See other patents in list of citations or searching for "television
ghost"

Heck, we did this stuff back at the university and that was a long time
before those kinds of patents. So if I'd dig a lot I'd probably find
prior art. However, the TV industry remained blissfully not interested.
That was in Europe and then the TV manufacturers keeled over one after
the other. Why was I not surprised about that?

 

[Jan Panteltje]

The stuff I remember (vaguely) was greatly refreshed by reading
<http://www.atsc.org/history.html> and the related pages on the
"Grand Alliance" and "FCC adopts...". They started with this
in the late 1980's, came up with several systems around 1991 and
combined the results into the standard by 1995.


I'm pretty sure that nobody had put up anything but a test transmitter
by then. I think some groups thought that they could lobby their way
around it as COFDM got better developed after 1995.

You also have to remember that in the decentralized US broadcast
industry, signal quality is a competitive tool. (Or used to be,
now that most everybody uses cable or satellite).

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

Yes, I have just read the links you mentioned.
Sure, in 1999 50% had access to ATSC transmissions.
Also this 50% experienced severe multipath problems.
The broadcasters, being 'competitive' did not really want to
lose viewers, and voices were hears (Sinclair for example) to
change to COFDM.
Of course the 'standard' was set, and it was a bit late to change.
As many had invested time and money in ATSC.

Cases like Joerg's show that sort of ignoring the problem is
no solution, what can he do?

It somehow reminds me of NTSC (we say Never Twice Same Color),
it was a new system, but it had flaws, it was not a bad system,
but sold with the flaws,
Maybe US should have been a bit more humble and review things in 1998,
as then COFDM results were also known.

I mean, ask yourself, IF US had known about PAL's line alternating phase,
WOULD it have adapted such a thing and not NTSC?

There are pride and ego and politics and money at work.
'We can always improve it later (can we?) and sell a new set'
guarantees continuous income for the industry.

 

[Bob Myers]

I mean, ask yourself, IF US had known about PAL's line alternating phase,
WOULD it have adapted such a thing and not NTSC?

Probably, but that's the whole point in that case - hindsight
is always 20/20. The developers of the NTSC system were
starting from scratch, whereas PAL was developed in an
environment where the real-world performance of the NTSC
method was already known, through a number of years of
actual experience. But it was certainly too late for those countries
which had already adopted NTSC to try to force a change on
their populace (and, as it turned out, little need to do so, since the
problems with NTSC diminished to insignificance with
continued improvements in receiver design).

SECAM, of course, is another thing altogether....;-)

Bob M.

 

[Jan Panteltje]

Probably, but that's the whole point in that case - hindsight
is always 20/20. The developers of the NTSC system were
starting from scratch, whereas PAL was developed in an
environment where the real-world performance of the NTSC
method was already known, through a number of years of
actual experience. But it was certainly too late for those countries
which had already adopted NTSC to try to force a change on
their populace (and, as it turned out, little need to do so, since the
problems with NTSC diminished to insignificance with
continued improvements in receiver design).

SECAM, of course, is another thing altogether....;-)

Bob M.

SECAM = Systeme Encenee Contre l'Amerique (excuse my French).
That means so much as 'System Created Against America'.
Now that was the time of Charles de Gaulle as French president.
Not a bad president, he gave France the bomb too.
SECAM was done together with the Russians, it was great for recording,
but you could not fade in or out... the color subcarrier was FM modulated.
So they used PAL in the studios.
http://en.wikipedia.org/wiki/SECAM

 

[Michael A. Terrell]

Probably, but that's the whole point in that case - hindsight
is always 20/20. The developers of the NTSC system were
starting from scratch, whereas PAL was developed in an
environment where the real-world performance of the NTSC
method was already known, through a number of years of
actual experience. But it was certainly too late for those countries
which had already adopted NTSC to try to force a change on
their populace (and, as it turned out, little need to do so, since the
problems with NTSC diminished to insignificance with
continued improvements in receiver design).

SECAM, of course, is another thing altogether....;-)

Bob M.

SECAM? I thought that was SCAM! ;-)


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Jim Thompson]

Probably, but that's the whole point in that case - hindsight
is always 20/20. The developers of the NTSC system were
starting from scratch, whereas PAL was developed in an
environment where the real-world performance of the NTSC
method was already known, through a number of years of
actual experience. But it was certainly too late for those countries
which had already adopted NTSC to try to force a change on
their populace (and, as it turned out, little need to do so, since the
problems with NTSC diminished to insignificance with
continued improvements in receiver design).

SECAM, of course, is another thing altogether....;-)

Bob M.

Yep. It takes a Frenchy to really screw things up ;-)

...Jim Thompson

 

[Vladimir Vassilevsky]

Jan Panteltje wrote:

SECAM = Systeme Encenee Contre l'Amerique (excuse my French).
That means so much as 'System Created Against America'.

And against Germans, too?

Now that was the time of Charles de Gaulle as French president.

Wasn't it at the times of Pompidou ?

SECAM was done together with the Russians,

SECAM was entirely bought by the USSR, including the schematics and the
valves for the TV sets. NTSC was considered also (that was during the
warming in relations of USSR and US (Sojuz - Apollo and such) ; SECAM
was preferred for the number of technical and political reasons.

it was great for recording,

SECAM can tolerate the poor quality channels, NTSC can't. The tuning
tolerances are much wider with SECAM, the delay lines do not have to be
very accurate. That used to be very important considerations at that
time. Phase distortions kill the NTSC. However in ideal conditions the
NTSC picture quality is better.

I can understand why the robustness was critical to Russians, but why
French did bother about at first time?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[David DiGiacomo]

No, the problem is the mandate. Fact is, analog works better.

Not in my experience. ATSC works much better for me (high signal, high
multipath environment).

Nope. Just bought a brand new one. Supposedly has a pretty good tuner.
Besides, I've heard from others who plunked down north of $2k that it
ain't much different for them either.

If it had a good tuner, you wouldn't have such problems. Take it back and
try a different brand. Who said anything about spending $2K?

That I might have to do, sacrifice some channels so that others can be
received better. This will mean a net reduction in TV content but fine
with me.

You might not have to sacrifice any channels.

Seriously, you can't possibly get a better one except by building your
own. Which, of course, is an option but TV ain't that important.

There is no such thing as a best TV antenna. It sounds like you could use
one with lower gain and better directionality.

If TV isn't important to you, why have you been posting about it so much?

That's what many out here will probably start doing.

So do it and be happy.

I am willing to make changes as long as they are reasonable. Signing up
for some $40-50/month cable deal isn't IMHO.

So far you've rejected every possible solution.

 

[Joerg]

Not in my experience. ATSC works much better for me (high signal, high
multipath environment).


If it had a good tuner, you wouldn't have such problems. Take it back and
try a different brand. Who said anything about spending $2K?

Well, I think a $750 set ought to do

You might not have to sacrifice any channels.


There is no such thing as a best TV antenna. It sounds like you could use
one with lower gain and better directionality.

If TV isn't important to you, why have you been posting about it so much?

Because I am not the only person out here and it is important to others,
for example older folks who can't move about much anymore. Many of them
don't have the means to plunk down another $40-50/month for cable. Those
folks sometimes depend on people like us to fix it when technical stuff
quits.

So do it and be happy.

Some day I will. But the local news aren't one there (yet).

So far you've rejected every possible solution.

I've only rejected the ones that aren't acceptable to me, like "oh, just
take it all back and spend more".

 

[Bob Myers]

SECAM = Systeme Encenee Contre l'Amerique (excuse my French).
That means so much as 'System Created Against America'.

In English, we typically would say "System Essentially Contrary
to the American Method"....;-)

Bob M.

 

[Joerg]

Jan Panteltje wrote:



And against Germans, too?


Wasn't it at the times of Pompidou ?


SECAM was entirely bought by the USSR, including the schematics and the
valves for the TV sets. NTSC was considered also (that was during the
warming in relations of USSR and US (Sojuz - Apollo and such) ; SECAM
was preferred for the number of technical and political reasons.


SECAM can tolerate the poor quality channels, NTSC can't. The tuning
tolerances are much wider with SECAM, the delay lines do not have to be
very accurate. That used to be very important considerations at that
time. Phase distortions kill the NTSC. However in ideal conditions the
NTSC picture quality is better.

I can only say that NTSC is also very good in non-ideal conditions.
Whenever this new ATSC stuff collapses I just switch to the old analog
channel and that works fine. Some distortion or flutter but clearly
visible. Of course, this will only work for another year or so.

I can understand why the robustness was critical to Russians, but why
French did bother about at first time?

Robust? Don't know about the hardware. I've heard some horror stories
about their older Raduga TV sets. Apartment fires and all that.

 

[Vladimir Vassilevsky]

Robust?

The main concern was the poor quality of the radio relay equipment.

Don't know about the hardware. I've heard some horror stories
about their older Raduga TV sets. Apartment fires and all that.

Those are not the stories. Our TV caught fire right before my eyes. The
horizontal scan module burned to ashes. After the repair shop refused, I
had to rebuid the TV; that was one of my first endeavours with electronics.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

 

[Joerg]

The main concern was the poor quality of the radio relay equipment.


Those are not the stories. Our TV caught fire right before my eyes. The
horizontal scan module burned to ashes. After the repair shop refused, I
had to rebuid the TV; that was one of my first endeavours with electronics.

I was told that they had a nickname for the older Radugas in East
Germany (when it was communist): "Zimmerbrand aus Freundesland". Loosely
translated "apartment fire delivered by an ally". IIRC they kept using a
really old stabilizing technology in the H-scan final: The ballast tube.
All the energy not used by the CRT was converted to heat so that the
stage load remained constant. Then, one fine day, phssst ... whoosh ...

 

[Jim Thompson]

On Tue, 27 Nov 2007 21:29:45 GMT, Joerg

[snip]

I was told that they had a nickname for the older Radugas in East
Germany (when it was communist): "Zimmerbrand aus Freundesland". Loosely
translated "apartment fire delivered by an ally". IIRC they kept using a
really old stabilizing technology in the H-scan final: The ballast tube.
All the energy not used by the CRT was converted to heat so that the
stage load remained constant. Then, one fine day, phssst ... whoosh ...

I remember that circuit ;-)

IIRC, Mad Man Muntz also used that in his designs.

My father had a policy... "We don't service Muntz TV sets".

...Jim Thompson

 

[Vladimir Vassilevsky]

I was told that they had a nickname for the older Radugas in East
Germany (when it was communist): "Zimmerbrand aus Freundesland". Loosely
translated "apartment fire delivered by an ally".

So they adopted SECAM in the East Germany to prevent the citizens from
watching the enemy propaganda. There is some logic to it.

IIRC they kept using a
really old stabilizing technology in the H-scan final: The ballast tube.

Yes. That was the exact copy of the original French design. In the later
mods, they removed the ballast tube and used the voltage multiplier for
the CRT anode; however the flammability remained about the same.

All the energy not used by the CRT was converted to heat so that the
stage load remained constant.

There was also a special shield with a warning about X-rays.

Then, one fine day, phssst ... whoosh ...

The flyback transformer was the most susceptible. High voltage, lots of
dust, heat, plastic isolation - a disneyland for fire.

VLV

 

[Joerg]

On Tue, 27 Nov 2007 21:29:45 GMT, Joerg

[snip]

I was told that they had a nickname for the older Radugas in East
Germany (when it was communist): "Zimmerbrand aus Freundesland". Loosely
translated "apartment fire delivered by an ally". IIRC they kept using a
really old stabilizing technology in the H-scan final: The ballast tube.
All the energy not used by the CRT was converted to heat so that the
stage load remained constant. Then, one fine day, phssst ... whoosh ...

I remember that circuit ;-)

IIRC, Mad Man Muntz also used that in his designs.

My father had a policy... "We don't service Muntz TV sets".

They sure were bone simple:
http://www.earlytelevision.org/muntz_17a3a.html

In Germany I staunchly refused to repair Kuba sets (just a name, they
had nothing to do with Fidel and his country). Later I refused to repair
any TV since their designs became so flimsy.

 

[Joerg]

So they adopted SECAM in the East Germany to prevent the citizens from
watching the enemy propaganda. There is some logic to it.

Supposedly they had other tricks, too. For example the clock in the
background was square and then they'd ask the kids in kindergarten to
describe it. If one of them mentioned a round clock ... "Aha!".

Yes. That was the exact copy of the original French design. In the later
mods, they removed the ballast tube and used the voltage multiplier for
the CRT anode; however the flammability remained about the same.


There was also a special shield with a warning about X-rays.

A friend who was a TV repair tech asked about that. His boss: "Oh, it
won't really harm you. It only causes impotence."

The flyback transformer was the most susceptible. High voltage, lots of
dust, heat, plastic isolation - a disneyland for fire.

Plus that dreaded soaked paper that they called insulating paper.

 

[Mark]

Joerg, I have been thinking about your case, where you have one direct path
and one airplane reflected path.
With 2 path destructive interference can cause zero signal.
Then I had this funny idea:
Why not use a wider beam antenna then your log periodic?
With some more refections the sum is not so likely to become zero...
But this will only work with sufficient signal strenth,

I turned my antenne 90 degrees to vertical, it is a bow tie, it has a wide angle.
I can now get some other stations, likely (but not 100% sure) one 120
miles away (40kW high tower), but some are now on the same frequency, so
hard to say if I get the one or the other...
There must be a station ID in the DTV tables, but I would have to look up the Etsi
documents, and write the soft to grab it perhaps.

the new receivers can adapt to multipath out to 50uS or so..

but they still have trouble when the mutipath is as strong as the
direct signal, and they still have some trouble when the multipath
changes with time i.e. dynamic multipath. The equalizer is adaptive
but it takes time to adapt. It sounds like your situation with the
aircraft in line with your antenna is a bad dynamic multipath
situation. You should contact the demod design companies and the FCC
and offer to them to use your location as a test site..

Sorry I don't have any helpful suggestions, get the receiver with the
best adaptive equlaizer and put up the best antenna you can.

Mark