| Author |
Message |
Guest
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 Posted:
Wed Sep 21, 2005 12:08 am Post subject:
Re: Q regarding television noise |
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On Tue, 20 Sep 2005 09:30:00 +0000 (UTC), "R. Mark Clayton"
<nospamclayton@btinternet.com> wrote:
| Quote: |
"Java Jive" <java@evij.com> wrote in message
news:432f5b61@news.greennet.net...
"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:432f2e89@news.usenetzone.com...
For us 15 to 20 kHz is at the edge of what most people can hear.
Yes, but it varies with age. Young people can hear frequencies up to
25KHz
absolute maximum, but that upper limit decreases with age. A group of us
tested our upper limit in the physics lab when I was in my late teens, my
upper limit was about 23KHz and the group average was above 20KHz. Just a
few years later in my early 20s, mine was already down to around 17KHz.
LCD TVs do not have a very good picture IMO, so I would not want to swap.
IMO LCDs have a superior picture to CRTs.
Yes they do by quite some margin IME, however for plasma screens many are
poorer due to low US style resolution of 852x480 (UK PAL has at least 576
displayed lines).
I have had a 32in Toshiba for about 7 years and the picture was to my |
mind as good as you can get. But the problem as I see it with normal
room size it was too big and heavy, every Hi Fi unit I stood it on
bent in the middle and had to be 152mm from the wall to accommodate
the huge lump that stuck out the back, so I took the plunge and
brought the latest Philips 32PF5520d HD LCD expecting to take a drop
in picture quality but I was presently surprised the picture to me is
as good as, not better perhaps, however when I watch DVD using
progressive scan then to my mind its better.
My point is that if I had a dozen people come to watch it,I think
that half would say it was worse, and the other half would say it was
a better picture than the old CRT, I think personally that picture
quality is in the eye of the beholder. I have a friend who shall be
nameless who has just invested in a new Flat screen Sony, got it home
switched it on and away went the auto install and all stations tuned
in and up came BBC one and the picture was to put mildly, awful,
contacted the store and told them he wanted it changed, as he had a
bad one, he then phoned me for my view on the subject so round I
went and knocked on his door, he was not in one of his best moods,
Looking at his TV cable I ask him when he last changed it, its only
about 25 years old he said, and why is your arial pointing at the moon
the wind did that last year that why we got a new telly the old
picture was crap, we can't afford a new arial we spent the money on a
new Tv
It does not matter if its CRT LCD or Plasma if the feed is crap
don't expect the best picture
Richard
The Mad Monk |
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Java Jive
Guest
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| Posted:
Wed Sep 21, 2005 5:25 am Post subject:
Re: Q regarding television noise |
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"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:43307c95@news.usenetzone.com...
| Quote: | On a sunny day (Tue, 20 Sep 2005 18:08:06 +0100) it happened "Java Jive"
java@evij.com> wrote in <43306971@news.greennet.net>:
If you are not a CRT diehard, you should apply similar reasoning to CRTs.
I
note that you don't, so I will: Assuming they are fortunate enough to be
so
in the beginning, a rare thing in itself, how many CRTs will still be in
perfect adjustment after seven years?
As you say, that is not a CRT issue but what you call 'delivery' issue.
|
I think you've misunderstood me (I guess Dutch is your first language, and
maybe I should try and word my posts accordingly, but I've always been
impressed by how well the Dutch speak foreign languages). In the context of
my previous mails in this thread, by 'delivery' I meant content/picture
delivery - ie: the signal source &/or the medium used to convey the signal
to the TV - because many of Zak's so-called anti-LCD points were actually
(valid) criticisms of shortcomings in the picture delivery, not of the LCDs
themselves. In effect, what I was saying was: "Garbage in, garbage out!"
'Delivery' in that context had nothing to do with delivering the TV to a
premises adjusted to a state fit to be watched.
| Quote: | That givens there ARE a lot of CRT TV sets out there that are aligned
horribly, but few weeks ago I walked into the store here and the LCDs were
completely wrong adjusted, white clipping, if I was Philips I would send
somebody to department stores like V&D here to teach them how to adjust
a set, people will NEVER buy the way that was set up.
And this is ASSUMING Philips can be better.
|
I'll take your word on that - given what I've already seen with CRTs, it
was likely to start happening with LCDs. Though don't forget that with both
types some of this is probably caused by shoppers playing with the remotes
....
| Quote: | 2) How long does your (if any) backlight last, and how much does it
cost
to
replace.
Both still going. How long will your tube last?
Well, you know I had a television repair shop, and a good tube last >10
years
if not longer.
|
Last one I had was less than that.
| Quote: | I have a small portable here that is 30 years old (transistor).
Its tube is bad..
|
So its relevance is?
| Quote: | I have an old cash terminal with BW tube in the attic, it is 35 years
old and the tube is 100%.
|
It's not just TVs and has nothing to do with CRT or LCD as such. All older
appliances tended to be built to last 'for the forseeable future' as the
modern phrase has it, while newer appliances are built to last five years if
you're lucky - we had a description for this phenomenon when it first
started to appear in the late 60s and early 70s: "Built-In obsolescence",
but now it's so normal that noone knows what that phrase means anymore!
| Quote: | 3) The gamma on ALL the LCDs I have seen in the shops suck, a CRT has
gamma 1/y^(2.2) by nature.
In case of LCD this is achieved electronically, and is it correct?
I've worked in the photographic trade on prints and enlargements, so
have at
least a reasonable eye, and both my LCDs give better colour balance than
any
CRT I can recall seeing, let alone have actually owned.
Gamma is not the same as color balance.
|
No, but you don't watch gamma, you watch a picture that either has a
realistic range of colours because the gamma and other settings are correct,
or it doesn't because they are not, and what I was saying is that I've never
yet seen a CRT with more realistic colours than my LCDs, mostly they are
nowhere near as good.
[snip ramblings]
| Quote: | Now let's look at the quality side of TV.
Tune to BBC (1,2,3,4) look at the technical quality they produce, it is
very good,
and it is free.
|
It's probably the best quailty available on UK Freeview, but nevertheless
it's overcompressed.
| Quote: | Now tune to RTL9, you have to pay, and it is crap technical quality.
|
I've certainly seen terrible quality on some sat channels too
| Quote: | The ONLY thing ...
|
[you're rambling again]
| Quote: | 5) The black level of a good CRT beats LCD.
As already explained, the contrast ratio of both is inadequate to cope
with
dark scenes followed by light scenes with no intervening adjustment -
for
optimum viewing of dark scenes with CRTs you have to reduce the
brightness
to avoid picture noise, with LCDs you have to reduce the backlight level.
No this is not correct.
|
It is correct. If you don't reduce the brightness control when a CRT is
showing something like the opening of "All The President's Men", you get
noise on the picture. I've noticed this with dark scenes from way back in
the 70s when there wasn't even an alternative technology to compare with
CRT, and it's been the same on every CRT I've ever used.
| Quote: | 6) The power consumption story is not really that true, look at the
watts
used.
I did ... LCD: Use 49W Standby 4W - *smaller* CRT: Use 52W, no
standby
figure given, I suspect it's higher than 4W.
The point is
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The point is you can't argue with the figures. |
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Jan Panteltje
Guest
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| Posted:
Wed Sep 21, 2005 4:08 pm Post subject:
Re: Q regarding television noise |
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On a sunny day (Wed, 21 Sep 2005 01:25:00 +0100) it happened "Java Jive"
<java@evij.com> wrote in <4330d05a$1@news.greennet.net>:
| Quote: | As you say, that is not a CRT issue but what you call 'delivery' issue.
I think you've misunderstood me (I guess Dutch is your first language, and
themselves. In effect, what I was saying was: "Garbage in, garbage out!"
'Delivery' in that context had nothing to do with delivering the TV to a
premises adjusted to a state fit to be watched.
No I understood you right. |
But you are clearly from a different (technical?) background.
Mine is electronics and broadcasting.
Anyways thank you for the compliments on my (the Dutch) English.
But I have worked and lived in London several years....
It helps.
For me (apart from the term 'delivery'), there is this:
camera (with gamma correction) - encoding system - transmitter -
receiver - receiver electronics - display device (CRT or LCD or
whatever, DLP what not).
In the olden days <<<<----- only CRT was used, and CRTs have a brightness
versus drive voltage curve so that for each n Volt increase in drive, the
brightness (light output) increases as n^2.2 (n to the power 2.2).
To keep receivers simple the transmitter compensates for this by distorting
the signal so it is as 1^(1/2.2).
This is not a bad thing it is a GOOD thing.
Because of the ^2.2 in the CRT, lower brightness level changes are less
'amplified' then the higher brightness ones in display.
The CRT curve is something like this:
L .
.
.
.
.
.. U(volts)
This is GOOD, because the noise is in the lower brightness areas in PAL,
in Europe the ANALOG TV transmitters transmit minimum if white, maximum
power if black (sync in fact).
So, when we have a low brightness scene in ANALOG TV, there is more noise.
The compensation (gamma correction) in the camera has the reverse curve:
L .
.
.
.
.
.. U
So you can see that the transmitter uses more dynamic range for the dark
noisy areas...
Overall (the whole system) this works as a noise reduction system, but
it ONLY works (100% good) if the curves are each other complement.
Of cause in digital TV we do not have the analog transmission problems.
For an LCD (or any display device) to display correctly it needs to have
the y^2.2 curve (imitate the CRT).
If the thing is 'linear' by itself, this curve needs to be made
electronically (as in the camera, sensors are linear).
| Quote: | It's not just TVs and has nothing to do with CRT or LCD as such. All older
appliances tended to be built to last 'for the forseeable future' as the
modern phrase has it, while newer appliances are built to last five years if
you're lucky - we had a description for this phenomenon when it first
started to appear in the late 60s and early 70s: "Built-In obsolescence",
but now it's so normal that noone knows what that phrase means anymore!
Oh, I absolutely agree with that, and now these days 'recycling' of materials... |
But build in obsolescence is not the same as build in bad solutions.
You can have a very high quality set that dies exactly after 100000 hours.
You can make it that way!
You can make a set with a terrible picture that last twice as long.
Perhaps the point is that (90%) of consumers (the ones that come after the
nerds like me that always want the latest tech, and know some stuff) wil buy
whatever the salesperson (thinks gives them max profit or empty old stock)
recommends.
I once went almost into a fit laughing in a computer shop when the guy was
selling 200 Watt PC speakers running from a 6 volt 300mA adapter (1.8 Watt
RMS INPUT, say 1W output).
'Yes sir, you are laughing, but (embarrassed) it REALLY is 200 Watts.
OK, bring some Tannoys and some heatsinks and some big stuff.
Now terms like 'HDTV ready' and what not, and these things do not even
have the correct number of pixels (LCD), come with what is it HDMI or
something, only designed so you cannot record from that interface, you are a
slave of Hollywood.
And on the other end - I have seen many movies on VHS (we used to rent tapes),
and of cause it did not always work well, but I have seen these.
Maybe a lot of stuff is left to imagination, I mean the super high resolution
is fun.... but in mpeg2 it stops being super high as soon as that newsreader
moves the head sideways.
Not to mention all the other artifacts around objects.
Always remember: mpeg2 is the mp3 of video!!!!!
Super high resolution on STILL images, and even then with artifacts, super
high resolution my foot.
Well I hope this reality check does not stop anyone from buying, it does not
stop me.
But some [technical] education for the general public would be in place.
It is their money. |
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laura fairhead
Guest
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| Posted:
Wed Sep 21, 2005 7:44 pm Post subject:
Re: Q regarding television noise |
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On Mon, 19 Sep 2005 21:23:22 GMT, Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:
| Quote: | On a sunny day (Mon, 19 Sep 2005 20:57:07 +0000 (UTC)) it happened
run_signature_script_for_my_email@INVALID.com (laura fairhead) wrote in
432f2539.5042825@news.btinternet.com>:
Hi ppl,
I have a quick question which is possibly not totally on-topic
but is related to television at least.... I am not an electrician
but have some knowledge of the basics and recently find myself
wondering about a phenomenon which I've noticed for a long time
now dealing with computer CRT's and television sets, namely
that they emit a very high pitched tone (possibly 15-20 khz)
when operating. I am wondering where this sound comes from
and how it is generated. The only thing I can observe is that
mains transformers emit a low pitched hum which must originate
from the low frequency AC oscillation and so I would suspect
the sound from the tv set was coming from the coil at the
rear of the CRT. Am I correct about that?
Correct, the (it is called deflection coils) use strong magnetic fields and
may vibrate.
More noise comes usually from the horizontal output transformer, that
is the transformer driving those coils (and associated inductors).
The core (a comprssed iron powder) consists of 2 pieces that will sometimes
strongly vibrate under influence of the magnetic field.
The 15625 Hz you hear is the horizontal scanning frequency, the little
spot that draws the picture on the TV moves 15625 times from left to right,
under influence of the magnetic fields of those deflection coils.
(And 50 times per second from top to bottom, there is also a 50 Hz noise).
|
Thanx Jan,
I had suspected something like it being the horizontal coils, yes you
can hear a 50hz tone if you are right next to the set (I suppose high
frequency sounds propagate further). I'm thinking of taking apart
a set now just have a look... :) This reminds me of another thing
I always wondered, basically, if current travels through a wire it
induces an electromagentic field so; apart from the sound would
there be a 15.625khz & 50hz electromagentic field emited from the
coils? I've always wonder about radio signals in the audio band,
namely whether they exist or whether there is some strange thing
going on, if I had a radio that didn't stop at the 150khz and
instead went right down to 50hz would I pick up a signal ?
| Quote: |
When we go HDTV on CRT or when you have a 100Hz TV the H frequency is higher
and above what we can hear.
I have heard stories of singing birds dying when people bought a (normal) TV
because they could not stand those high pitches.
|
hehe :) Maybe a HDTV will kill mosquittos ? ;-)
| Quote: | For us 15 to 20 kHz is at the edge of what most people can hear.
LCD TVs should not have this problem, but may still use some converter that
makes noise...
LCD TVs do not have a very good picture IMO, so I would not want to swap.
|
byefornow
laura
| Quote: |
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Jan Panteltje
Guest
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| Posted:
Thu Sep 22, 2005 12:08 am Post subject:
Re: Q regarding television noise |
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On a sunny day (Wed, 21 Sep 2005 19:44:47 +0000 (UTC)) it happened
run_signature_script_for_my_email@INVALID.com (laura fairhead) wrote in
<4331b75d.21818004@news.btinternet.com>:
| Quote: | I had suspected something like it being the horizontal coils, yes you
can hear a 50hz tone if you are right next to the set (I suppose high
frequency sounds propagate further).
Hi. |
The horizontal power is somewhat higher too.
| Quote: | I'm thinking of taking apart
a set now just have a look... :) This reminds me of another thing
Please unplug it first, and note that high voltages may still be present |
(charged capacitors).
| Quote: | I always wondered, basically, if current travels through a wire it
induces an electromagnetic field so; apart from the sound would
there be a 15.625khz & 50hz electromagentic field emited from the
coils?
Yes there is, the field in the deflection coils is mainly focused |
inside the coils, that of the transformers in the core.
But there is always some leakage.
| Quote: | I've always wonder about radio signals in the audio band,
namely whether they exist or whether there is some strange thing
going on, if I had a radio that didn't stop at the 150khz and
instead went right down to 50hz would I pick up a signal ?
Yes these VLF (Very Low Frequencies) are even used to communicate, |
for example with submarines, as that is the only thing that goes through
water.
If you have an old tape recorder, like perhaps a walkman, hold it next to
the TV (without tape in it), and press play, you should hear the 50 Hz hum.
the magnetic head should pick it up.
These days there are strict regulations to how much RF radiation is allowed
to come from a monitor for example.
My Samsung SyncMaster has a metal cage inside for screening.
But you cannot 100% screen for magnetic fields.
| Quote: | hehe :) Maybe a HDTV will kill mosquittos ? ;-)
I have read that those ultrasonic devices do not do much, I have a lamp |
with electric wires in it for that purpose.
But any bit that helps is OK of cause :-)
Jan |
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laura fairhead
Guest
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| Posted:
Tue Sep 27, 2005 9:37 pm Post subject:
Re: Q regarding television noise |
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On Wed, 21 Sep 2005 20:07:29 GMT, Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote:
| Quote: | I've always wonder about radio signals in the audio band,
namely whether they exist or whether there is some strange thing
going on, if I had a radio that didn't stop at the 150khz and
instead went right down to 50hz would I pick up a signal ?
Yes these VLF (Very Low Frequencies) are even used to communicate,
for example with submarines, as that is the only thing that goes through
water.
If you have an old tape recorder, like perhaps a walkman, hold it next to
the TV (without tape in it), and press play, you should hear the 50 Hz hum.
the magnetic head should pick it up.
|
hI jAN,
Sorry to take so long to come back on this but I've been thinking
and experimenting! Well, cheers for the advice - I tried it the other
day and could hear the hum, also I noticed that the sound varies with the
picture content so that has started me investigating other things...! :)
Now, when things are very very quiet, I can also hear the audio of that
hum and the picture interference. What I would really like to do would be to
build a directional aerial to pick up those waves,... something that
would be extremely sensitive only picking up waves where you point
it (like a satellite dish), I reckon this would make a great electronics
probe tool (wouldn't be surprised at all if someone had done this
already - you could connect it to an oscilloscope or a computer and
to see the results and it would be unintrusive as well.)
Anyway thanx again, your answers are always informative
and interesting :-)
byefornow
laura
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Jan Panteltje
Guest
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| Posted:
Wed Sep 28, 2005 3:16 pm Post subject:
Re: Q regarding television noise |
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On a sunny day (Tue, 27 Sep 2005 21:37:18 +0000 (UTC)) it happened
run_signature_script_for_my_email@INVALID.com (laura fairhead) wrote in
<4339b9d2.19216374@news.btinternet.com>:
| Quote: | hI jAN,
Sorry to take so long to come back on this but I've been thinking
and experimenting! Well, cheers for the advice - I tried it the other
day and could hear the hum, also I noticed that the sound varies with the
picture content so that has started me investigating other things...! :)
Now, when things are very very quiet, I can also hear the audio of that
hum and the picture interference. What I would really like to do would be to
build a directional aerial to pick up those waves,... something that
would be extremely sensitive only picking up waves where you point
it (like a satellite dish), I reckon this would make a great electronics
probe tool (wouldn't be surprised at all if someone had done this
already - you could connect it to an oscilloscope or a computer and
to see the results and it would be unintrusive as well.)
Anyway thanx again, your answers are always informative
and interesting :-)
byefornow
laura
Hi, this 'eavesdropping' is used for espionage and authorities monitoring |
you.
For getting info from a TV or monitor screen there are basically 2 ways.
First is the radio wave spectrum monitoring.
In a CRT rather high frequencies are used to drive the 3 electron guns for
red green and blue.
The voltages will be 10 to 100 V perhaps in amplitude.
The frequency for normal 625 lines PAL is limited to about 5 MHz bandwidth, so you have
a spectrum from 0 - 5 MHz, or perhaps 15625Hz to 5MHz.
This can indeed be picked up with an antenna from some distance.
For a computer monitor the max frequency is much higher, and depends on the
screen format, it can go up above 100MHz.
The second way we can eavesdrop, is by using reflected light from the CRT.
As the electron spot scans across the screen, it varies in brightness.
Because of the slowness of our eyes we see a constant picture.
When you use a fast photodetector, you can get this intensity signal, and
with some signal processing get the original picture back.
You do NOT need to look directly at the screen, an adversary with a telescope
can monitor your house and use reflected light from the ceiling for example.
Here is a paper showing what can be done for example:
http://www.cl.cam.ac.uk/~mgk25/ieee02-optical.pdf
The Usenet newsgroup you want for this is sci.crypt.
I am there too ....
There are other ways too, in normal TVs the incoming frequency is converted
to a fixed intermediate frequency, around 30 to 39 MHz, this is amplified
and has rather large amplitude.
This signal sometimes radiates a bit and can be picked up too.
Also the local oscillator in teh tuner may radiate, allowing you to calculate
what station (frequency) the set is tuned to, without seeing the picture.
Recent tests I did show that it is possible to pick up harmonics in the
30 to several hundred kHz range from the horizontal frequency with a simple
ferrite rod, and that way see what station the set is locked to (H sync).
There are many signal sources in a TV set that can give you away...
CU later... |
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