# CRT monitor query: Relationship between video input bandwidth and refresh rate/resolution settings p

Discussion in 'Electronic Basics' started by Ken Moiarty, Apr 14, 2006.

1. ### Ken MoiartyGuest

Hi, I'm trying to search the web for 19" to 22" CRT monitors on the market
which provide the *highest refresh rates per a certain range of resolutions
(e.g. starting at 1024 x 768 thru to 1600 x 1200). In other words, I'm
looking for monitor product specs that show a list of resolutions and their
corresponding maximum refresh rates as would be presented in a table. This
is hard to tailor a Google search for.

Therefore for keyword terms, I'm turning my attention to "video input
bandwidth" (rated on the order of hundreds of mHz, rather than the mere tens
of Hz that apply to vertical refresh rates) as a search term/variable to use
in my searching. In my browsing I get the impression that the higher the
value of this "video input bandwidth" parameter, the higher the refresh rate
possible for a given resolution (when all other things being equal, of
course). But I seem unable to find anything to confirm this hunch.

If someone here, who is more knowledgeable than I on this subject, could
please enlighten (and/or correct) me here, or just point me towards a good
faq site on this topic, I'd appreciate it very much. For example, is there
any kind of linear mathematical relationship between a monitor's video input
bandwidth value, and it's refresh rate values relative to various possible
resolutions? Or perhaps you might just tell me what might be the upper
limit or ceiling in terms of the maximum "video input bandwidth" values
realistically obtainable (e.g. 300mHz?, 350mHz?, 900mHz?, what?). Then I
could have some idea of what range of values I might begin punching into my
Google search attempts (as in, 'try this and see what me comes up with',
etc...etc...) .

TIA,

Ken

--------------------------------------------------------------------------------------------

* FYI, for those who just may be curious: Because of local problem of 60 Hz
alternating magnetic-field interference emanating from a major high voltage
powerline corridor running right through part of my back yard, in order to
make good use of a CRT monitor I have to run it at refresh rates that are
multiples of 60 Hz (e.g. 60 Hz, 120 Hz, 180 Hz, etc.).

One might think the preferred alternative might be to just get an LCD
monitor (or if spending gobs of money for ugly aesthetics were somehow not
objectionable, have a custom made mu-metal monitor-enclosure made). The
complicating factor here is however is for my purposes here an LCD monitor
won't do. (I have already invested in an LCD monitor for regular computer
use.) Here I'm looking for a monitor which I can use for viewing very
high-quality high-resolution Stereo 3-D video, and this can only be done
using a large CRT monitor.

Further necessitating the desire to search for a CRT monitor based on the
highest refresh rates available, not only must this monitor refresh at some
multiple of 60 Hz to avoid local electromagnetic interference as I just
mentioned, but because of the demands of high quality stereo 3-D viewing the
vertical refresh rate absolutely cannot be anything less than 120 Hz;
although in fact a somewhat higher refresh rate than 120 Hz (e.g. 135 Hz) is
preferable in order to avoid noticeable flicker during 3-D viewing. (This is
only because, although the monitor is refreshing at 120 Hz, stereo 3-D video
is using two vertical scans to produce one interlaced stereo 3-D frame,
meaning the actual stereo 3-D refresh rate rate is still a mere 60 Hz as far
as each eye is permitted to see (due to the stereo 3D shutter glasses).
This results in flicker just like that experienced with a monitor set to 60
Hz refresh rate for general use.) Therefore given the constraints imposed
by my powerline interference problem, to achieve a monitor refresh rate
above 120 Hz, I would have to leap to the next multiple of 60 Hz, which
would of course be 180 Hz refresh rate. And to achieve this refresh rate in
and of itself, it is not difficult to find a monitor capable of 180 Hz.
What is proving difficult however (for me at least) is finding a monitor
that can refresh at 180 Hz whilst display at 1024 x768 or higher resolution!

And btw, not even this is the end of the story: In addition to the above
requirement, the monitor's horizontal sync frequency must be no less than
126 kHz --ideally 130-140 kHz. Thus I must be sure to avoid any monitor in
which this parameter has been compromised by the manufacturer the interest
of competitive pricing, knowing that many monitor buyers will simply not be
aware in this regard. But this parameter simply is not mentioned or even
referred to in the specs provided for any of the CRT monitor models I've so
far been able read about on the web. (See
http://pymol.sourceforge.net/stereo3d.html , if anyone wants to see the
source of my info pertaining stereo 3-D video.)

Ken Moiarty, Apr 14, 2006

2. ### Mark MGuest

"Ken Moiarty" <> wrote in message news:...
> Hi, I'm trying to search the web for 19" to 22" CRT monitors on the market
> which provide the *highest refresh rates per a certain range of resolutions
> (e.g. starting at 1024 x 768 thru to 1600 x 1200). In other words, I'm
> looking for monitor product specs that show a list of resolutions and their
> corresponding maximum refresh rates as would be presented in a table. This
> is hard to tailor a Google search for.
>
> Therefore for keyword terms, I'm turning my attention to "video input
> bandwidth" (rated on the order of hundreds of mHz, rather than the mere tens
> of Hz that apply to vertical refresh rates) as a search term/variable to use
> in my searching. In my browsing I get the impression that the higher the
> value of this "video input bandwidth" parameter, the higher the refresh rate
> possible for a given resolution (when all other things being equal, of
> course). But I seem unable to find anything to confirm this hunch.
>
> If someone here, who is more knowledgeable than I on this subject, could
> please enlighten (and/or correct) me here, or just point me towards a good
> faq site on this topic, I'd appreciate it very much. For example, is there
> any kind of linear mathematical relationship between a monitor's video input
> bandwidth value, and it's refresh rate values relative to various possible
> resolutions? Or perhaps you might just tell me what might be the upper
> limit or ceiling in terms of the maximum "video input bandwidth" values
> realistically obtainable (e.g. 300mHz?, 350mHz?, 900mHz?, what?). Then I
> could have some idea of what range of values I might begin punching into my
> Google search attempts (as in, 'try this and see what me comes up with',
> etc...etc...) .
>
> TIA,
>
> Ken
>
>
>
> --------------------------------------------------------------------------------------------
>
>
> * FYI, for those who just may be curious: Because of local problem of 60 Hz
> alternating magnetic-field interference emanating from a major high voltage
> powerline corridor running right through part of my back yard, in order to
> make good use of a CRT monitor I have to run it at refresh rates that are
> multiples of 60 Hz (e.g. 60 Hz, 120 Hz, 180 Hz, etc.).
>
> One might think the preferred alternative might be to just get an LCD
> monitor (or if spending gobs of money for ugly aesthetics were somehow not
> objectionable, have a custom made mu-metal monitor-enclosure made). The
> complicating factor here is however is for my purposes here an LCD monitor
> won't do. (I have already invested in an LCD monitor for regular computer
> use.) Here I'm looking for a monitor which I can use for viewing very
> high-quality high-resolution Stereo 3-D video, and this can only be done
> using a large CRT monitor.
>
> Further necessitating the desire to search for a CRT monitor based on the
> highest refresh rates available, not only must this monitor refresh at some
> multiple of 60 Hz to avoid local electromagnetic interference as I just
> mentioned, but because of the demands of high quality stereo 3-D viewing the
> vertical refresh rate absolutely cannot be anything less than 120 Hz;
> although in fact a somewhat higher refresh rate than 120 Hz (e.g. 135 Hz) is
> preferable in order to avoid noticeable flicker during 3-D viewing. (This is
> only because, although the monitor is refreshing at 120 Hz, stereo 3-D video
> is using two vertical scans to produce one interlaced stereo 3-D frame,
> meaning the actual stereo 3-D refresh rate rate is still a mere 60 Hz as far
> as each eye is permitted to see (due to the stereo 3D shutter glasses).
> This results in flicker just like that experienced with a monitor set to 60
> Hz refresh rate for general use.) Therefore given the constraints imposed
> by my powerline interference problem, to achieve a monitor refresh rate
> above 120 Hz, I would have to leap to the next multiple of 60 Hz, which
> would of course be 180 Hz refresh rate. And to achieve this refresh rate in
> and of itself, it is not difficult to find a monitor capable of 180 Hz.
> What is proving difficult however (for me at least) is finding a monitor
> that can refresh at 180 Hz whilst display at 1024 x768 or higher resolution!
>
> And btw, not even this is the end of the story: In addition to the above
> requirement, the monitor's horizontal sync frequency must be no less than
> 126 kHz --ideally 130-140 kHz. Thus I must be sure to avoid any monitor in
> which this parameter has been compromised by the manufacturer the interest
> of competitive pricing, knowing that many monitor buyers will simply not be
> aware in this regard. But this parameter simply is not mentioned or even
> referred to in the specs provided for any of the CRT monitor models I've so
> far been able read about on the web. (See
> http://pymol.sourceforge.net/stereo3d.html , if anyone wants to see the
> source of my info pertaining stereo 3-D video.)

Here's a relatively recent link (Jan 2006) that lists CRT models you'll
probably still be able to find:
http://pymol.sourceforge.net/stereo3d.html

Mark M, Apr 14, 2006

3. ### Guest

In sci.electronics.basics Ken Moiarty <> wrote:
>Hi, I'm trying to search the web for 19" to 22" CRT monitors on the market
>which provide the *highest refresh rates per a certain range of resolutions
>(e.g. starting at 1024 x 768 thru to 1600 x 1200). In other words, I'm
>looking for monitor product specs that show a list of resolutions and their
>corresponding maximum refresh rates as would be presented in a table. This
>is hard to tailor a Google search for.

>Therefore for keyword terms, I'm turning my attention to "video input
>bandwidth" (rated on the order of hundreds of mHz, rather than the mere tens
>of Hz that apply to vertical refresh rates) as a search term/variable to use
>in my searching. In my browsing I get the impression that the higher the
>value of this "video input bandwidth" parameter, the higher the refresh rate
>possible for a given resolution (when all other things being equal, of
>course). But I seem unable to find anything to confirm this hunch.

>If someone here, who is more knowledgeable than I on this subject, could
>please enlighten (and/or correct) me here, or just point me towards a good
>faq site on this topic, I'd appreciate it very much. For example, is there
>any kind of linear mathematical relationship between a monitor's video input
>bandwidth value, and it's refresh rate values relative to various possible
>resolutions? Or perhaps you might just tell me what might be the upper
>limit or ceiling in terms of the maximum "video input bandwidth" values
>realistically obtainable (e.g. 300mHz?, 350mHz?, 900mHz?, what?). Then I

300 mHz = .3 Hz.. watch out with those suffixes.

Anyway:

X_pixels * Y_pixels * Vertical_refresh * Nth_harmonic = Bandwidth
(asfair)

One person mentioned one should have a monitor that manages 3rd harmonic
to get that "crisp" video. While you will get a picture at 1st harmonic

So for a 1600x1200 pixel @ 60 Hz:
1600*1200*60*3 = 345600000 Hz = 345.6 MHz

, Apr 14, 2006
4. ### CWattersGuest

<> wrote in message
news:443f9f0f\$0\$491\$...
> X_pixels * Y_pixels * Vertical_refresh * Nth_harmonic = Bandwidth
> (asfair)
>
> One person mentioned one should have a monitor that manages 3rd harmonic
> to get that "crisp" video. While you will get a picture at 1st harmonic

>
> So for a 1600x1200 pixel @ 60 Hz:
> 1600*1200*60*3 = 345600000 Hz = 345.6 MHz

Minor addition to the above...

There should be a a factor of 1/2 in there somewhere because the max
frequency occurs with alternate black and white pixels. Draw the square wave
and you can see the base frequency is half the pixel rate.

CWatters, Apr 14, 2006
5. ### KenGuest

lid wrote:
>
> 300 mHz = .3 Hz.. watch out with those suffixes.
>

Whoops.

> Anyway:
>
> X_pixels * Y_pixels * Vertical_refresh * Nth_harmonic = Bandwidth
> (asfair)
>
> One person mentioned one should have a monitor that manages 3rd harmonic
> to get that "crisp" video. While you will get a picture at 1st harmonic

Being an electronics layperson I'm not sure what, "manages 3rd
harmonic", refers to. Would this have something to do with the role of
a "3-comb filter"?

>
> So for a 1600x1200 pixel @ 60 Hz:
> 1600*1200*60*3 = 345600000 Hz = 345.6 MHz

Terrific! Thank you.

Ken

Ken, Apr 15, 2006
6. ### Jasen BettsGuest

On 2006-04-14, Ken Moiarty <> wrote:
> Hi, I'm trying to search the web for 19" to 22" CRT monitors on the market
> which provide the *highest refresh rates per a certain range of resolutions
> (e.g. starting at 1024 x 768 thru to 1600 x 1200). In other words, I'm
> looking for monitor product specs that show a list of resolutions and their
> corresponding maximum refresh rates as would be presented in a table. This
> is hard to tailor a Google search for.
>
> Therefore for keyword terms, I'm turning my attention to "video input
> bandwidth" (rated on the order of hundreds of mHz, rather than the mere tens
> of Hz that apply to vertical refresh rates) as a search term/variable to use
> in my searching. In my browsing I get the impression that the higher the
> value of this "video input bandwidth" parameter, the higher the refresh rate
> possible for a given resolution (when all other things being equal, of
> course). But I seem unable to find anything to confirm this hunch.

sounds right to me... basically if your source emits pixels at greater than
twice the bandwidth the display will not respond fast enough to distinguish
individual pixels. that's the "ceiling" thing start blurring out before that
point, somewhere above half the bandwidth the effect begins to become
noticable.

> If someone here, who is more knowledgeable than I on this subject, could
> please enlighten (and/or correct) me here, or just point me towards a good
> faq site on this topic, I'd appreciate it very much.

> For example, is there
> any kind of linear mathematical relationship between a monitor's video input
> bandwidth value, and it's refresh rate values relative to various possible
> resolutions?

no. the scan and video signals don't intterract inside the monitor
(until they both meet at the CRT)

> Or perhaps you might just tell me what might be the upper
> limit or ceiling in terms of the maximum "video input bandwidth" values
> realistically obtainable (e.g. 300mHz?, 350mHz?, 900mHz?, what?).

Define realisitic. tubes could be made with bandwiths in the low gigahertz
without too much trouble. if they aren't already like that.

> * FYI, for those who just may be curious: Because of local problem of 60 Hz
> alternating magnetic-field interference emanating from a major high voltage
> powerline corridor running right through part of my back yard, in order to
> make good use of a CRT monitor I have to run it at refresh rates that are
> multiples of 60 Hz (e.g. 60 Hz, 120 Hz, 180 Hz, etc.).

ah... TVs do that too...

but at 120Hz wouldn't 60Hz interferance deflect alternate scans in the
opposite direction?

> What is proving difficult however (for me at least) is finding a monitor
> that can refresh at 180 Hz whilst display at 1024 x768 or higher resolution!

the video bandwidth is proportional to the maximum number of pixels
times the refresh rate.

> And btw, not even this is the end of the story: In addition to the above
> requirement, the monitor's horizontal sync frequency must be no less than
> 126 kHz --ideally 130-140 kHz.

768*180 = 138240 Hz , if it can do 768 lines at 180 Hz the horizontal rate
will be over 138 kHz, probably over 140kHz.

> Thus I must be sure to avoid any monitor in
> which this parameter has been compromised by the manufacturer the interest
> of competitive pricing, knowing that many monitor buyers will simply not be
> aware in this regard. But this parameter simply is not mentioned or even
> referred to in the specs provided for any of the CRT monitor models I've so
> far been able read about on the web. (See
> http://pymol.sourceforge.net/stereo3d.html , if anyone wants to see the
> source of my info pertaining stereo 3-D video.)

you will be able to use the product scanlines * refreshrate to approximate
the horizontal rate (add about 20 to scanlines to account for the vertical
retrace period)

eg: if aa display can do 1200 lines at 120Hz refresh rate it can do
800 lines at 180Hz, and to avchieve either it needs over 144Khz horizontal
rate.

Bye.
Jasen

Jasen Betts, Apr 15, 2006
7. ### CWattersGuest

"Ken" <> wrote in message
news:...
> lid wrote:
> Being an electronics layperson I'm not sure what, "manages 3rd
> harmonic", refers to. Would this have something to do with the role of
> a "3-comb filter"?

No. If you want nice sharp edges on your pixels you need to feed tham a
square wave not a sine wave. To make a square wave you need a mixture of
more than one sine wave. To make a square wave with infinitly steep edges
would need to use an infinite number of odd harmonics (multiples of
1,3,5,7,9...) of the base frequency. To make one with reasonably steep edges
you only need a few (perhaps only the third) harmonic.

http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

CWatters, Apr 15, 2006
8. ### Mark MGuest

"CWatters" <> wrote in message news:Ub20g.373321\$-ops.be...
>
> "Ken" <> wrote in message
> news:...
> > lid wrote:
> > Being an electronics layperson I'm not sure what, "manages 3rd
> > harmonic", refers to. Would this have something to do with the role of
> > a "3-comb filter"?

>
> No. If you want nice sharp edges on your pixels you need to feed tham a
> square wave not a sine wave. To make a square wave you need a mixture of
> more than one sine wave. To make a square wave with infinitly steep edges
> would need to use an infinite number of odd harmonics (multiples of
> 1,3,5,7,9...) of the base frequency. To make one with reasonably steep edges
> you only need a few (perhaps only the third) harmonic.
>
> http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

Yes, but there's a practical consideration as well. If you operate
a CRT monitor at or even near its bandwidth limit, image quality
will suffer terribly. Quite a bit of headroom is required to avoid
this issue.

Mark M, Apr 15, 2006
9. ### Gene E. BlochGuest

On 4/15/2006, CWatters posted this:
> "Ken" <> wrote in message
> news:...
>> lid wrote:
>> Being an electronics layperson I'm not sure what, "manages 3rd
>> harmonic", refers to. Would this have something to do with the role of
>> a "3-comb filter"?

>
> No. If you want nice sharp edges on your pixels you need to feed tham a
> square wave not a sine wave. To make a square wave you need a mixture of
> more than one sine wave. To make a square wave with infinitly steep edges
> would need to use an infinite number of odd harmonics (multiples of
> 1,3,5,7,9...) of the base frequency. To make one with reasonably steep edges
> you only need a few (perhaps only the third) harmonic.
>
> http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

And to clarify for Ken, the self-confessed "electronics layperson", a
periodic wave is composed of a fundamental frequency, which is the
frequency we associate with the wave, and various integer multiples of
that frequency. These are called harmonics or overtones.

The first harmonic is the base frequency. The second harmonic is twice
that frequency, the third three times that, and so on. Other important
factors are the amplitudes and phases of these harmonics, which
determine the exact wave shape.

Computing all the phases and amplitudes will be left as an exercise for

The first overtone is the same as the second harmonic, and so on. The
fundamental would be the zeroth overtone, but it's not conventional to
use that term.

Gino

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

Gene E. Bloch, Apr 16, 2006
10. ### Tom MacIntyreGuest

On Sat, 15 Apr 2006 17:10:16 -0700, Gene E. Bloch
<> wrote:

>On 4/15/2006, CWatters posted this:
>> "Ken" <> wrote in message
>> news:...
>>> lid wrote:
>>> Being an electronics layperson I'm not sure what, "manages 3rd
>>> harmonic", refers to. Would this have something to do with the role of
>>> a "3-comb filter"?

>>
>> No. If you want nice sharp edges on your pixels you need to feed tham a
>> square wave not a sine wave. To make a square wave you need a mixture of
>> more than one sine wave. To make a square wave with infinitly steep edges
>> would need to use an infinite number of odd harmonics (multiples of
>> 1,3,5,7,9...) of the base frequency. To make one with reasonably steep edges
>> you only need a few (perhaps only the third) harmonic.
>>
>> http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

>
>And to clarify for Ken, the self-confessed "electronics layperson", a
>periodic wave is composed of a fundamental frequency, which is the
>frequency we associate with the wave, and various integer multiples of
>that frequency. These are called harmonics or overtones.
>
>The first harmonic is the base frequency. The second harmonic is twice
>that frequency, the third three times that, and so on. Other important
>factors are the amplitudes and phases of these harmonics, which
>determine the exact wave shape.

Some would argue that what you refer to as the first harmonic is the
fundamental, with the first harmonic being twice that of the
fundamental.

Tom

>
>Computing all the phases and amplitudes will be left as an exercise for
>
>The first overtone is the same as the second harmonic, and so on. The
>fundamental would be the zeroth overtone, but it's not conventional to
>use that term.
>
>Gino

Tom MacIntyre, Apr 16, 2006
11. ### KenGuest

Gene E. Bloch wrote:
> On 4/15/2006, CWatters posted this:
> > "Ken" <> wrote in message
> > news:...
> >> lid wrote:
> >> Being an electronics layperson I'm not sure what, "manages 3rd
> >> harmonic", refers to. Would this have something to do with the role of
> >> a "3-comb filter"?

> >
> > No. If you want nice sharp edges on your pixels you need to feed tham a
> > square wave not a sine wave. To make a square wave you need a mixture of
> > more than one sine wave. To make a square wave with infinitly steep edges
> > would need to use an infinite number of odd harmonics (multiples of
> > 1,3,5,7,9...) of the base frequency. To make one with reasonably steep edges
> > you only need a few (perhaps only the third) harmonic.
> >
> > http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

>
> And to clarify for Ken, the self-confessed "electronics layperson", a
> periodic wave is composed of a fundamental frequency, which is the
> frequency we associate with the wave, and various integer multiples of
> that frequency. These are called harmonics or overtones.
>
> The first harmonic is the base frequency. The second harmonic is twice
> that frequency, the third three times that, and so on. Other important
> factors are the amplitudes and phases of these harmonics, which
> determine the exact wave shape.
>
> Computing all the phases and amplitudes will be left as an exercise for
> the reader ;-)
>
> The first overtone is the same as the second harmonic, and so on. The
> fundamental would be the zeroth overtone, but it's not conventional to
> use that term.
>
> Gino

Thanks for your clarification on this term, "harmonics". It occurs to
me that I might do myself a favor by spending some time studying up a
bit on all what's involved in CRT monitor technology... all the terms
and concepts, etc...

Ken

Ken, Apr 17, 2006
12. ### KenGuest

> but at 120Hz wouldn't 60Hz interferance deflect alternate scans in the
> opposite direction?

All I can tell you is that 120 Hz was suggested to me, and then having
tried it with a CRT monitor in my house, it seemed to resolve the
interference problem pretty much just like the 60 Hz setting does
(except minus the bothersome "60 Hz" flicker ). But I only tried it
briefly (being that I had to downgrade the resolution setting
unacceptably for the CRT monitor I have to refresh at 120 Hz) and thus
maybe not thoroughly enough (e.g. during the usual time of day when the
powerline interference is at it's worst -e.g. between 9-11 PM). It
didn't occur to me that there might be any theoretical reason not to
expect this to either work fully or to not work at all. Now that you
bring this up, I think I'll test it again; only this time I'll take
greater care to be sure to rule out any remote possibility that the PL
interference doesn't just happen to be at one of its temporary ebbs at
that particular moment.

Thanks,

Ken

Ken, Apr 17, 2006
13. ### Bob MyersGuest

"Jasen Betts" <> wrote in message
news:...
> sounds right to me... basically if your source emits pixels at greater

than
> twice the bandwidth the display will not respond fast enough to

distinguish
> individual pixels. that's the "ceiling" thing start blurring out before

that
> point, somewhere above half the bandwidth the effect begins to become
> noticable.

Some clarification is in order here, I think. Besides that, it's fun
to write about a display technology that I haven't had to worry
about professionally for nearly 10 years...

CRTs, and analog video in general, don't know a thing about
"pixels." There are no distinct pixels in either the video signal
or in the displayed image. Bandwidth, or better yet rise/fall time,
is all there is.

You would at first glance think that "bandwidth" IS in fact going
to be the relevant specification here, but that turns out not to be
the case - nor is it necessary that the specified or measured
BW of the video amplifier be high enough to capture the 3rd
harmonic of half the pixel rate (since HALF the pixel rate, as
mentioned before, is the fastest rate at which you would see
a supposed "square wave" representing alternative black/white
lines). Due to a number of factors, not the least of which are the
spot size of the CRT and the additional "sampling" effect of the
color CRT phosphor dot and shadow mask structure, increases
in BW beyond a point much higher than about the pixel rate itself
(as a rough rule of thumb) will not result in a visible improvement
in the image quality. Further, a "bandwidth" spec is often
very misleading - depending on how it is measured, "bandwidth"
measurements may not take into account slew-rate limiting at
the CRT cathode, which is really what you want to worry about
when it comes to looking at the quality of alternating vertical lines
and similar single-pixel detail.

The bottom line is that in a CRT, you're basically aiming for
rise and fall times (at the full video swing) of perhaps 1/3 to
1/2 the pixel period, maximum, as measured at the CRT
cathode.

> Define realisitic. tubes could be made with bandwiths in the low gigahertz
> without too much trouble. if they aren't already like that.

They're not, nor can they readily be made anywhere near that high.
With typical cathode drive, you're talking about swinging a signal over
the low tens of volts range (20-40V signal swings at the cathode are
common) and fairly capacitive load. Gigahertz bandwidth here would
be expensive to achieve, but fortunately was never really necessary.

> > And btw, not even this is the end of the story: In addition to the

above
> > requirement, the monitor's horizontal sync frequency must be no less

than
> > 126 kHz --ideally 130-140 kHz.

>
> 768*180 = 138240 Hz , if it can do 768 lines at 180 Hz the horizontal rate
> will be over 138 kHz, probably over 140kHz.

[some deleted]
> eg: if aa display can do 1200 lines at 120Hz refresh rate it can do
> 800 lines at 180Hz, and to avchieve either it needs over 144Khz horizontal
> rate.

In terms of the horizontal rate, you're correct - but in the vast
majority of CRT monitor designs, the VERTICAL rate will be
limited such that you can't ever get to much about 120 Hz, no
matter what the horizontal range might imply.

Bob M.

Bob Myers, Apr 17, 2006
14. ### Gene E. BlochGuest

On 4/16/2006, Tom MacIntyre posted this:
> On Sat, 15 Apr 2006 17:10:16 -0700, Gene E. Bloch
> <> wrote:
>
>> On 4/15/2006, CWatters posted this:
>>> "Ken" <> wrote in message
>>> news:...
>>>> lid wrote:
>>>> Being an electronics layperson I'm not sure what, "manages 3rd
>>>> harmonic", refers to. Would this have something to do with the role of
>>>> a "3-comb filter"?
>>>
>>> No. If you want nice sharp edges on your pixels you need to feed tham a
>>> square wave not a sine wave. To make a square wave you need a mixture of
>>> more than one sine wave. To make a square wave with infinitly steep edges
>>> would need to use an infinite number of odd harmonics (multiples of
>>> 1,3,5,7,9...) of the base frequency. To make one with reasonably steep
>>> edges you only need a few (perhaps only the third) harmonic.
>>>
>>> http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

>>
>> And to clarify for Ken, the self-confessed "electronics layperson", a
>> periodic wave is composed of a fundamental frequency, which is the
>> frequency we associate with the wave, and various integer multiples of
>> that frequency. These are called harmonics or overtones.
>>
>> The first harmonic is the base frequency. The second harmonic is twice
>> that frequency, the third three times that, and so on. Other important
>> factors are the amplitudes and phases of these harmonics, which
>> determine the exact wave shape.

>
> Some would argue that what you refer to as the first harmonic is the
> fundamental, with the first harmonic being twice that of the
> fundamental.
>
> Tom

They would not be physicists, then.

See my next paragraph about overtones.

>> Computing all the phases and amplitudes will be left as an exercise for
>> the reader ;-)
>>
>> The first overtone is the same as the second harmonic, and so on. The
>> fundamental would be the zeroth overtone, but it's not conventional to
>> use that term.
>>
>> Gino

Gino (again)

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

Gene E. Bloch, Apr 18, 2006
15. ### Gene E. BlochGuest

On 4/16/2006, Ken posted this:
> Gene E. Bloch wrote:
>> On 4/15/2006, CWatters posted this:
>>> "Ken" <> wrote in message
>>> news:...
>>>> lid wrote:
>>>> Being an electronics layperson I'm not sure what, "manages 3rd
>>>> harmonic", refers to. Would this have something to do with the role of
>>>> a "3-comb filter"?
>>>
>>> No. If you want nice sharp edges on your pixels you need to feed tham a
>>> square wave not a sine wave. To make a square wave you need a mixture of
>>> more than one sine wave. To make a square wave with infinitly steep edges
>>> would need to use an infinite number of odd harmonics (multiples of
>>> 1,3,5,7,9...) of the base frequency. To make one with reasonably steep
>>> edges you only need a few (perhaps only the third) harmonic.
>>>
>>> http://hyperphysics.phy-astr.gsu.edu/Hbase/audio/geowv.html

>>
>> And to clarify for Ken, the self-confessed "electronics layperson", a
>> periodic wave is composed of a fundamental frequency, which is the
>> frequency we associate with the wave, and various integer multiples of
>> that frequency. These are called harmonics or overtones.
>>
>> The first harmonic is the base frequency. The second harmonic is twice
>> that frequency, the third three times that, and so on. Other important
>> factors are the amplitudes and phases of these harmonics, which
>> determine the exact wave shape.
>>
>> Computing all the phases and amplitudes will be left as an exercise for
>> the reader ;-)
>>
>> The first overtone is the same as the second harmonic, and so on. The
>> fundamental would be the zeroth overtone, but it's not conventional to
>> use that term.
>>
>> Gino

>
> Thanks for your clarification on this term, "harmonics". It occurs to
> me that I might do myself a favor by spending some time studying up a
> bit on all what's involved in CRT monitor technology... all the terms
> and concepts, etc...
>
> Ken

You know, I might have been more help if I hadn't left out some vital
information...

An important other thing about this expression of periodic waves as a
series of harmonics is that a representation of a given periodic wave
as a limited series of harmonics will be an imperfect representation of
the original signal. The accuracy of that representation will increase
as more harmonics are included. In additon, the harmonics that are
present are subjct to phase errors and amplitude errors, all of which
change the shape of the signal.

Anyway, the above considerations lead us to ideas of what's good
enough, which relates directly to the criterion that we should have at
least the third harmonic present in the signal amplifier.

Gino

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

Gene E. Bloch, Apr 18, 2006
16. ### Ken MoiartyGuest

I've now been able to re-test this. What I've found upon closer inspection
is that the 120 Hz setting does indeed improve the PL interference, but not
really quite as entirely as the 60 Hz setting does (i.e. there is still
some, albeit barely noticeable, "jitter"). What I didn't expect however,
(and this turns my "multiples-of-60Hz-hypothesis" on it head) is that when I
put the refresh rate even higher than 120 Hz (e.g. to 144 Hz or 150 Hz), the
interference problem _remains_ improved as it is at the 120 Hz setting.
Obviously the reduction in noticeable interference experienced at 120 Hz has
nothing to do with that refresh rate being a whole-number multiple of the 60
Hz, and everything to do with it just being a substantially higher refresh
rate. Thus it appears I was wrong in my conclusion that to view high
resolution stereo 3D video I needed a CRT monitor capable of displaying
those resolutions at a full 180 Hz. This could make my search to buy a
suitable CRT monitor for this purpose a tiny bit easier.

Ken

"Ken" <> wrote in message
news:...
>> but at 120Hz wouldn't 60Hz interferance deflect alternate scans in the
>> opposite direction?

>
> All I can tell you is that 120 Hz was suggested to me, and then having
> tried it with a CRT monitor in my house, it seemed to resolve the
> interference problem pretty much just like the 60 Hz setting does
> (except minus the bothersome "60 Hz" flicker ). But I only tried it
> briefly (being that I had to downgrade the resolution setting
> unacceptably for the CRT monitor I have to refresh at 120 Hz) and thus
> maybe not thoroughly enough (e.g. during the usual time of day when the
> powerline interference is at it's worst -e.g. between 9-11 PM). It
> didn't occur to me that there might be any theoretical reason not to
> expect this to either work fully or to not work at all. Now that you
> bring this up, I think I'll test it again; only this time I'll take
> greater care to be sure to rule out any remote possibility that the PL
> interference doesn't just happen to be at one of its temporary ebbs at
> that particular moment.
>
> Thanks,
>
> Ken
>

Ken Moiarty, Apr 18, 2006
17. ### Gene E. BlochGuest

Ken, a thought has been nagging at me for a day or so.

If the problem with your monitor is truly due to the nearby power
lines, could it possibly be improved by reorienting the monitor?

My though is that the monitor might be oriented parallel to the
oscillating magnetic files, and rotating the monitor so it's
perpendicular to those fields may actually help.

BTW, feel free to swap parallel and perpendicular in the above
sentence, since I have no idea what exactly causes the physical
effects. also consider in-between angles.

In my office layout, there is no way that I could change the
orientation of my monitor. If you have the same problem, I offer
sympathy

The other possibility is to put up a screen of mu-metal, a magnetic
shielding material. You could probably do it for \$1000, maybe even less
- it's not cheap stuff. Just wasting bandwidth on this idea

HTH,
Gino

On 4/18/2006, Ken Moiarty posted this:
> I've now been able to re-test this. What I've found upon closer inspection
> is that the 120 Hz setting does indeed improve the PL interference, but not
> really quite as entirely as the 60 Hz setting does (i.e. there is still some,
> albeit barely noticeable, "jitter"). What I didn't expect however, (and this
> turns my "multiples-of-60Hz-hypothesis" on it head) is that when I put the
> refresh rate even higher than 120 Hz (e.g. to 144 Hz or 150 Hz), the
> interference problem _remains_ improved as it is at the 120 Hz setting.
> Obviously the reduction in noticeable interference experienced at 120 Hz has
> nothing to do with that refresh rate being a whole-number multiple of the 60
> Hz, and everything to do with it just being a substantially higher refresh
> rate. Thus it appears I was wrong in my conclusion that to view high
> resolution stereo 3D video I needed a CRT monitor capable of displaying those
> resolutions at a full 180 Hz. This could make my search to buy a suitable
> CRT monitor for this purpose a tiny bit easier.
>
> Ken
>
>
> "Ken" <> wrote in message
> news:...
>>> but at 120Hz wouldn't 60Hz interferance deflect alternate scans in the
>>> opposite direction?

>>
>> All I can tell you is that 120 Hz was suggested to me, and then having
>> tried it with a CRT monitor in my house, it seemed to resolve the
>> interference problem pretty much just like the 60 Hz setting does
>> (except minus the bothersome "60 Hz" flicker ). But I only tried it
>> briefly (being that I had to downgrade the resolution setting
>> unacceptably for the CRT monitor I have to refresh at 120 Hz) and thus
>> maybe not thoroughly enough (e.g. during the usual time of day when the
>> powerline interference is at it's worst -e.g. between 9-11 PM). It
>> didn't occur to me that there might be any theoretical reason not to
>> expect this to either work fully or to not work at all. Now that you
>> bring this up, I think I'll test it again; only this time I'll take
>> greater care to be sure to rule out any remote possibility that the PL
>> interference doesn't just happen to be at one of its temporary ebbs at
>> that particular moment.
>>
>> Thanks,
>>
>> Ken
>>

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

Gene E. Bloch, Apr 18, 2006
18. ### Gene E. BlochGuest

On 4/18/2006, Gene E. Bloch posted this:

<SNIP A LOT>

> My though is that the monitor might be oriented parallel to the oscillating
> magnetic files,

Interesting concept, magnetic files. Of course I meant magnetic fields.

Gino

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

Gene E. Bloch, Apr 18, 2006
19. ### Ken MoiartyGuest

"Gene E. Bloch" <> wrote in message
news:...
> Ken, a thought has been nagging at me for a day or so.
>
> If the problem with your monitor is truly due to the nearby power lines,
> could it possibly be improved by reorienting the monitor?
>
> My though is that the monitor might be oriented parallel to the
> oscillating magnetic files, and rotating the monitor so it's perpendicular
> to those fields may actually help.
>
> BTW, feel free to swap parallel and perpendicular in the above sentence,
> since I have no idea what exactly causes the physical effects. also
> consider in-between angles.

Well it was a worthy try. I just gave your suggestion a try, but to no
avail (at least to no noticeable avail). Seems the only CRT related option
here is to obtain a monitor capable of, both, at least 1024 x 768 (although
my preference would be 1280 x1024) resolution, @ 120 Hz (give or take)
refresh rate, simultaneously. So far it appears that monitor models on the
market that match (or exceed) this capability are far and few between and
therefore not likely to be found in a local vendor selling CRT monitors at
good-value prices.

>
> The other possibility is to put up a screen of mu-metal, a magnetic
> shielding material. You could probably do it for \$1000, maybe even less -
> it's not cheap stuff. Just wasting bandwidth on this idea

Well the mu-metal option is not all that outrageous really. It's just that
(1) it would be strictly utilitarian (i.e not cool to look at) and (2) for
about the same investment I can buy a higher performance CRT monitor
(through one of a handful of online vendors I've just found) that will
provide the high refresh rate that will also do the trick here, whilst enjoy
the luxury of the additional features and other (if you will) 'thoughtful
touches' that come with a CRT monitor in that price range. For example:
the 22" (20" viewable) Iiyama HM204DT, which sports a video input bandwidth
of 390 MHz and will handily display 1280 x 1024 at a solid 133 Hz... Its
MSRP is \$699. And from what I can discern it is (to be brief) 'loaded'!
Actually the more I think about it the more I'm inclined to just submit my
credit card number and buy it right now. But such impulse buying is a
weakness of mine that I must try to hold myself back from. So I'm going to
wait until my 'infatuation' with the idea wears off a little so I can
possibly weigh the decision more rationally and objectively. <g>

Ken

Ken Moiarty, Apr 20, 2006
20. ### Ken MoiartyGuest

No problem. I'm not that easily confused. <g>

Ken

"Gene E. Bloch" <> wrote in message
news:...
> On 4/18/2006, Gene E. Bloch posted this:
>
> <SNIP A LOT>
>
>> My though is that the monitor might be oriented parallel to the
>> oscillating magnetic files,

>
> Interesting concept, magnetic files. Of course I meant magnetic fields.
>
> Gino
>
>
> --
> Gene E. Bloch (Gino)
> letters617blochg3251
> (replace the numbers by "at" and "dotcom")
>
>

Ken Moiarty, Apr 20, 2006