TV to VGA conversion - why so hard/expensive?

What is so special or difficult about converting a TV signal to a VGA signal, that a "TV tuner" box costs between $100 and $300, just to put a TV signal onto a VGA monitor? -- (NO computer running -- dont forget that, please).  We are NOT talking here about PC cards, I am only talking about using a SVGA monitor instead of a Televison.

Going the opposite way, you can buy a $5 adapter to convert SVGA to TV signal, which is price realistic.

I would like a BRIEF *technical explanation* as to why it is/is not so hard to convert TV scan lines to work on a VGA.  I simply dont believe it costs that much to make a TV-to-VGA converter box, I think it is a total rip off.

I think Mfgs are scamming the public.  It should be SO simple to put half the lines on double the Pixel dimensions, and fudge the refresh rate to 2X what TV uses - in fact, electronically, it should be almost trivial.  Please give only electronic signal conversion descriptions, and how it could be easily done.  Please focus on CONCISE electronic descriptions, not links, not lengthy pasted excerpts, and not other side issues.  Thank you.  

BRIEF ELECTRONIC EXPLANATIONS ONLY PLEASE.  NO LINKS PLEASE.
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scrathcyboyAsked:
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Irwin SantosComputer Integration SpecialistCommented:
It's the laws of supply and demand.
scrathcyboyAuthor Commented:
Going the opposite way, you can buy a $5 adapter to convert SVGA to TV signal, which is price realistic.  Hence it should cost only about $10 to make a TV to SVGA converter.

irwinpks, that is not a technical description.  Please read the question.  This is important.
Irwin SantosComputer Integration SpecialistCommented:
Though technically sound as you mention that it "shouldn't be that hard" to make such device, there is not enough demand to warrant such cause. This impacts extra cost that you "may" or "may not" need.  Why put this feature into a system where 99% of the population will not use it?  You're just adding cost to the over all component.

This solution shouldn't be techical in sense, it's more economics.
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Irwin SantosComputer Integration SpecialistCommented:
@scratchcyboy...please see my followup.
scrathcyboyAuthor Commented:
As the question asks, I am interested in electronic descriptions of the conversion, not economic opinions.
nltechCommented:
well, sorry. you're getting a link.. :)

it isn't *that* difficult to translate from an ntsc signal to vga. here's the plans for such a converter. we built this sort of stuff in high school electronics classes.

http://elm-chan.org/works/sc/report.html

what you do find, however, is that retail products designed to take a tv signal and output to vga, is that they include things like tuners and remote controls. they may also support more than one standard (e.g. ntsc & pal).

that's what really drives the price up (that, plus it's a specialty niche item that there's not a whole lot of demand for)... nothing technical about it at all.

newegg does have one tv to vga box for a lot less, see http://www.newegg.com/Product/Product.asp?Item=N82E16815100114 runs 59.99 plus shipping, and there's a 20.00 rebate on top of that.
Irwin SantosComputer Integration SpecialistCommented:
@scrathcyboy...as you can see nltech concurs what I first commented on.
nltechCommented:
i actually that that wrote for a previous question (yesterday) that he asked, which was pretty much the same, but it was deleted before i got to submitting it.
scrathcyboyAuthor Commented:
nltech, please provide a brief description here of the conversion.  If it is high school material, then it should be trivial to build it, correct?  So it should not be that hard to describe it, correct?  Thank you.
Irwin SantosComputer Integration SpecialistCommented:
@scratcyboy...here is that schematics....within the above link that nltech supplied
http://elm-chan.org/works/sc/sc_dist.png

Locate the components that are marked.  You can us a breadboard or etch your own circuit board. Locate a go electronics parts store that carries pcboard making supplies.  This looks like a good project for a day.
scrathcyboyAuthor Commented:
Since neither of you seem to understand this question, and you want to paste links, look at THIS LINK --

http://cgi.ebay.com/NEW-VGA-to-TV-CONVERTER-S-VIDEO-RCA-OUT-CABLE-ADAPTER_W0QQitemZ9706144066QQcategoryZ41999QQrdZ1QQcmdZViewItem

Now tell me, why cannot that same cable be made to go the other way around.  THAT is what I am asking.  Nothing to do with elaborate boxes with components soldered onto it, there it is in a CABLE !!
Irwin SantosComputer Integration SpecialistCommented:
go electronics = good electronics
Irwin SantosComputer Integration SpecialistCommented:
inside the D-molded head is a circuit board that does what is mentioned above.  Small parts = lower cost.  Made in China/Taiwan, = even lower cost.
scrathcyboyAuthor Commented:
irwinpks, so far you have added nothing to this Q that I did not already know.
I will await others for what was asked in the original question ( if not already lost in above comments) --

I would like a BRIEF *technical explanation* as to why it is/is not so hard to convert TV scan lines to work on a VGA. Please focus on CONCISE electronic descriptions, not links, not lengthy pasted excerpts, and not other side issues.  BRIEF ELECTRONIC EXPLANATIONS ONLY PLEASE
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
Here's a link which discusses the reasons why the conversion is difficult

http://www.tkk.fi/Misc/Electronics/circuits/vga2tv/video2vga.html

Plus circuitry and components and such.
nltechCommented:
heh. i found another page on that same site...
>> RGB signal ouput from VGA card is already standard 0.7Vpp to 75 ohm load.
from http://www.tkk.fi/Misc/Electronics/circuits/vga2rgbs.html


i would highly recommend a little reading material...
http://www.amazon.com/gp/product/0071437150  (this is a project-based book)
http://www.amazon.com/gp/product/1878707566
http://www.amazon.com/gp/product/024080614X
(theses may be available from your library as well)


scrathcyboyAuthor Commented:
thank you dbrunton, that link was OK, but I disagree with the author -- most scan converters default to interlaced anyway, and since nltechs first link showed it is only a 2X doubling of H. freq and the V. freq is the same, then I am still missing what cant be done with a simple cable + tiny electronics, Asian style.

SO to nltech and dbrunton, my question is this, to double the H. refresh convert to interlaced scanning and approx. the same V.refresh, we need only one oscillator and a few other tiny components, is this correct?  Seems to me that elaborate transistors and other similar expensive components not necessary, is this true?
scrathcyboyAuthor Commented:
Or maybe better way to say, Cable input is serial pulsed signal with composite video in series pulses, so we need serial decoder, to split into RGB channels, then interlace and resize to double scan rate and H refresh rate.  This circuit has been available in Televisions for more than 20 years, it now costs $1 max?
Irwin SantosComputer Integration SpecialistCommented:
@scrathcyboy...not to be totally seemed "out of the picture"...I'm just trying to see what you want in your questions result...  Are you just looking for confirmation why it's so expensive, or are you looking to provide a product that will solve the cost factor?  Perhaps develope a product?
scrathcyboyAuthor Commented:
IF we understand electronics involved, we know what electronic components needed to solve problem.  Realize, cost of designing yourself is totally unrelated to a "production cost".  So to build a home project is irrelevant to Q, of what electronic processes occur, hence what components needed.  I understand mass production cost well, from Asian Mfgs - am not interested in making a box.  I always try to understand the functioning of everything I work with, you will see this in my answers to all questions on expert exchange.  I suspect we are being ripped off, I want someone to prove to me at the electronic component level that yes, the conversion is too difficult to build it into a $5 cable, as theyve done for the opposite conversion.  It is a knowledge quest - I can perfectly well translate it to a cost factor, as long as knowledge is accurate.
scrathcyboyAuthor Commented:
anyway, it has been a dull evening, and you 3 contributors livened it up a lot, maybe I split points 3 ways?
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
And I don't think this link has been posted

http://www.epanorama.net/links/videocircuits.html#tvvga

Its more that just hsync and vsynch



scrathcyboyAuthor Commented:
OK, that article, with its atrocious english, does present a grim picture.  Then, for the most points, why does it work so simply in reverse i.e. why is VGA to TV scan conversion such a simple $5 task, any idea??
dbruntonQuid, Me Anxius Sum?  Illegitimi non carborundum.Commented:
If you have a SCART socket then this link

http://www.qsl.net/dh1dm/tv_50hz_svga/

then scroll down to

How to connect a TV set to the VGA card output connector

and see the circuitry involved.

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scrathcyboyAuthor Commented:
AHA !! ASM language programming chipsets, that I do understand.

I think I close this question now with the following 4 way assignment, hope you understand.
Thanks for all the input, especially dbrunton on the technical aspects of the programming.

The conclusion is, I think (?) I was right, TV to VGA conversion SHOULD cost no more than VGA to TV ???
PCBONEZCommented:
Brief technical explaination. (Basic)

Modulation = Superimposing a signal over a carrier frequency.

VGA signal to TV.
All that's needed is to modulate the signal into RF.
Only one frequency needs supported by the converter.
The TV's tuner does the rest.

TV signal to VGA.
You need a tuner/demodulator.
Many frequencies must be supported. (Unless you only want one channel.)
More parts = more money.

Input to tuner is not one signal, it's a whole bunch of signals mixed together.
The signal goes into the tuner which strips out all the unwanted frequencies leaving just the desired one. (Channel)
Then it goes through a demodulator that strips out the carrier frequency leaving just the video signal.

That's much more complicated than taking a video signal and modulating it into one RF signal.
.
PCBONEZCommented:
It shouldn't cost much more.
~~ IF you only want ONE channel.

Nobody's gonna make one like that 'cause who'd buy a TV tuner to VGA gadget that could only do one channel????
.
scrathcyboyAuthor Commented:
sorry PCBONEZ, that came in 10 seconds after I accepted the other peoples input.  Next time I give it to you?

Future reader realize, PCBONEZ input was exactly what I wanted, a little earlier, he would have got most of the points.  Sorry PCBONEZ, will make up next time -- again !!!  
scrathcyboyAuthor Commented:
Just out ot reply to PCBONEZs last comment, with Satellite TV, you need only ONE channel, 73 or 60, that is all, since the satellite remote tune for you, the receiver need be set to ONLY ONE CHANNEL -- YES !!!
PCBONEZCommented:
It was just timing. Don't worry about it...

TV to VGA means converting an RF signal into a video signal. -video signal out-
VGA to TV means converting a video signal into RF. -RF out-

In your Satellite TV example the all you are doing is using two tuners instead of one.
The output of the Satillite tuner to the TV is one channel of -RF-.
It's not a video signal.
The example is closer to the $5 adapter you mentioned in the initial question because the output is RF.
.
scrathcyboyAuthor Commented:
So is it realistic to suggest that $5 adapter just to convert TV to VGA for one channel, either 60 or 73, or do we pay 10x that for features never used?  You see the stupidity of hype marketing - everyone - I hope?

PC BONEZ -- If you want to add more, I give separate question for your input, your input is exactly what I wanted, I should have waited, but since I would like to know the facts, you say whatever you want, and I decide how to handle it, and it will be OK...
PCBONEZCommented:
It's not worth the hassle to move the question. Don't worry about points.

A tuner is basically just an adjustable frequency filter.
They are expensive relative to other parts because they have to handle many frequenices.
 
If you have a set frequency (one channel) then the other componets you would need are.
An RF amplifier (makes the RF signal large enough for the demodulator).
-- This could be simpler 'than normal' RF amp because it only needs to pass one frequency.
The demodulator (strips the carrier signal out)
-- This could be simpler 'than normal' demodulator because it only needs to handle one frequency.
A signal amps for sound and video (boosts the output of the demodulator to usable levels.)
Video driver circuit (to convert the signal to a VGA output.)
Audio driver circuit (to convert the sound to a speaker output.)
Probably an audio amp unless the speakers are amplified.

Forgot about sound, din' ya??
.
Irwin SantosComputer Integration SpecialistCommented:
@scrathcyboy...enlightening....thank you for the points!! :-)
scrathcyboyAuthor Commented:
PCBONEZ, I would like to take up this again in a new question.  Let me know when you are there.
PCBONEZCommented:
If I'm on it's usually between late PM and early AM Arizona time (GMT-7).
I'll aswer what I can but depending on where you are going with this I may already be at the limit of my usefull input.
I was in Electronics but my practical experience is in NUC power plant Control Systems. I pull my Communications equipment knowledge out of the way-back machine from messing with Radars and Radios during my basic electronics training back in the early 1980's. That was a long time ago.
scrathcyboyAuthor Commented:
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