[opendtv] Re: Fcc Question

The standard pixel format for characters always included at least one column
that was blank to provide for spacing between characters, and at least one
pixel row between rows of characters.  If you wanted underline function, you
needed at least two largely blank rows below characters (sometimes three for
clarity of the underline when the character has a dangler, like the
character 'g'. where part goes below the base line.

 

So, it's already in the math.  In a windows PC, you can play with some of
these modes by going to the command window, right-clicking on the title bar,
click on "properties" then the "font" tab.

 

John Willkie

 

  _____  

De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Barry Wilkins
Enviado el: Friday, June 22, 2007 12:59 AM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: Fcc Question

 

But although there are 70 pixels per character and 80 characters per line,
does this include spacing between the characters horizontally and vertically
for readability? Is this where some of the extra bandwidth is needed?

Barry 

On 6/22/07, John Shutt <shuttj@xxxxxxxxx> wrote:

Apparently the fudge factor is 50%

8.4 MHz x 1.5 = 12.6 MHz, Larry's given answer.

John

----- Original Message -----
From: "John Limpert" < john.a.limpert@xxxxxxxxx
<mailto:john.a.limpert@xxxxxxxxx> >
To: <opendtv@xxxxxxxxxxxxx>
Sent: Thursday, June 21, 2007 4:58 PM
Subject: [opendtv] Re: Fcc Question


> The first thing I'd do is compute the necessary dot clock. 
>
> 70 * 25 * 80 * 60 = 8.4E6 Hz
>
> You then need to multiply it by a fudge factor to allow time for sync
> and retrace. As far as the total video bandwidth is concerned, that's
> going to also depend on how much smearing of the video signal is 
> considered to be acceptable.
>
> On 6/21/07, Larry Bloomfield <Larry@xxxxxxxxxxxxx> wrote:
>> Hi all:
>>
>> I have a question for you.  I have been studying the FCC element 8 for 
>> radar and several of the questions have been making me crazy.  One goes
>> like this
>>
>> A shipboard raster scan radar has a CRT with the following
>> characteristics:  70 pixels per character, 80 characters per line, 25 
>> lines per screen and it scans 60 screens per second.
>>
>> What is the minimum required bandwidth for the electron beam control
>> signal.
>>
>> The answer is 12.6MHz ,  and I'll be dammed if I can figure out how they
>> came up wit this figure.  I have searched the web and all they talk
>> about is pixels and refresh rates.
>>
>> I know that there are 140,000 pixels on this screen or 2000 characters i 
>> think.
>>
>> Any ideas as to how it is calculated or where might I go to find out???
>>
>>
>>
>>
>> --
>> Larry Bloomfield - KA6UTC
>> 1980 25th St. - Florence, OR 97439 
>> (541) 902-2424 (My Everything Phone #)
>> WWW.Tech-Notes.TV
>> See you on the Tech-Notes Taste of NAB 2007 Road Show
>
>
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