TV as an Oscilloscope

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Michael-love-electronics
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TV as an Oscilloscope

Post by Michael-love-electronics » Fri Dec 19, 2003 1:39 pm

Hi everyone,..<p> I really need an 150MHz oscilloscope that can show the waveforms of the FM signals but when I asked about the price I was shocked,.. Someone told me that I can use the TV as an oscscope.<p> Does anyone know how could I do this.???????<p> I'll appreciate your help.<p> Thanks :) :) :) :)

samsmiles
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Re: TV as an Oscilloscope

Post by samsmiles » Fri Dec 19, 2003 2:41 pm

Hi Michael,
check this out:
http://www.dansworkshop.com/Homebuilt%2 ... cope.shtml<p>Also check December 2003 issue of circuit cellar
http://www.dtweed.com/circuitcellar/xlandbru.htm#2832
And Bruce Lands web at cornell:
http://instruct1.cit.cornell.edu/course ... /lab4.html
Good luck
Sam<p>[ December 19, 2003: Message edited by: Sam Smiles ]</p>

k7elp60
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Re: TV as an Oscilloscope

Post by k7elp60 » Fri Dec 19, 2003 2:44 pm

I don't know about the digital TV bandwidth's,but
I don't think a analog TV will work as the horizontal fregency is 15.525Khz and the vertical is 60Hz. These are US standards.<p>What FM signals do you want to view on an oscilloscope?

samsmiles
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Re: TV as an Oscilloscope

Post by samsmiles » Fri Dec 19, 2003 5:31 pm

yeah K7 maximum sample rate is 15.75 kHz which is the NTSC video line rate! Good point. Not sure about the project now as well :-( Sorry Michael
Sam

russlk
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Re: TV as an Oscilloscope

Post by russlk » Fri Dec 19, 2003 6:42 pm

The TV resolution is not very good, using the PC as an oscope is better. Designs are available but the bandwidth is audio, 150 mHz would require some memory so the waveform could be stored and displayed in delayed time. I don't know if anyone has done this.

rshayes
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Re: TV as an Oscilloscope

Post by rshayes » Fri Dec 19, 2003 7:50 pm

Each horizontal line could be used to display one sample. This would give a sampling rate of 15.75 KHz. It would also draw the trace vertically rarher than horizontally.<p>By digitizing the samples, storing them in memory, and then reformatting them, a horizontal display could be made. The logic required could probably be implemented in one of the CPLDs sold by DigiKey and others. Speed would be a problem, since the sampling rate for a 150 MHz waveform should probably be at least 500 MHz.<p>A few articles describing sampling adapters for conventional oscilloscopes were published in the 1950's and 1960's, but these usually used exotic circuits such as avalanche transistor pulse generators and microwave mixer diodes.<p>An alternate approach is to convert the signal to a lower frequency, probably using two balanced mixers with quadrature local oscillator signals, and using a low frequency scope to observe the waveform.

Michael-love-electronics
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Re: TV as an Oscilloscope

Post by Michael-love-electronics » Sat Dec 20, 2003 9:24 am

Thanks Guys for all your help :) <p> If the TV didn't work, would the computer monitor work.????
OR,
Is there any circuit I can build to make a scale so that I 1000Hz on my waveform represents by 1Hz on the TV.?????
i.e: each 1000Hz --------> 1 Hz
As you said that the Horizontal freq is 15KHz.<p> Thanks very much

Michael-love-electronics
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Re: TV as an Oscilloscope

Post by Michael-love-electronics » Sun Dec 21, 2003 3:26 pm

Hi,..<p> Although the frequency of the TV doesn't match with the freq of my FM transmitter, I still wonder:
<"How could I use the TV as an Oscope.?????">
What connections, settings I have to do.???
Also, <"can I use the computer graphics card and the monitor as an Oscope.???"><p>Can anyone help....... :) :) :) :) Thanks :D

Chris Foley
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Re: TV as an Oscilloscope

Post by Chris Foley » Sun Dec 21, 2003 5:01 pm

Hi, Mike. A TV is too slow. The PC trick you're talking about is actually using the sound card input as a digitizing oscilloscope, with the display generated through a PC program and displayed on the monitor. There are shareware programs out there to do this, but alas, again way too slow.<p>The way to use a PC as a high speed oscilloscope is to buy a scope card, which acts like a digital oscilloscope on a PC card. It's a pretty expensive solution (usually just about the same as buying a free-standing scope), with some annoying noise limitations under certain circumstances.<p>There are times when you just have to bite the bullet, but before you do, you might want to look at the prices on used scopes, and also seeing if you can't borrow use of one for a while. Usually, the scope is the "big ticket item" where most hobbyists decide to stop investing, which is unfortunate since it's so useful and saves so much time. Also try bankruptcy auctions -- you'd be suprised how many businesses have good scopes which go on the block when they go under. Look at Don Lancaster's site for information on these auctions and how to work them to your advantage. One piece of free advice -- a used Tektronix is usually about the same price as a new off-brand, but I think it's usually a better investment.<p>Don Lancaster's Tinaja.com<p>Give yourself a Christmas present this year, Mike. You deserve it.<p>Good luck.
Chris<p>[ December 21, 2003: Message edited by: Chris Foley ]</p>

Dean Huster
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Re: TV as an Oscilloscope

Post by Dean Huster » Sun Dec 21, 2003 5:04 pm

You must've been shocked at the price of the scope because you were looking at new models. Digital scopes are just now coming into their own at decent NEW prices, but if you want to stay within a reasonable budget, there's not a darned thing wrong with an analog scope and there's plenty of them with the bandwidth you need on ebay. A Tektronix 465, 465M, 465B, 464, 466 and 468 all have 100MHz BW; the Tek 475 and 475A are 200 and 250MHz respectively; the 485 comes in at 350MHz; a 7603 with 7A26 & 7B53A will handle 100MHz; a 7704A with 7A26 & 7B53A (or better timebase) will handle 250MHz. Any of those models are high-end, high-quality instruments that often go for under $300. Most are available in such quantity that repair parts are easily available from inexpensive "hangar queens".<p>Needless to say, I'm not one for buying a new scope vs. a good used one.<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

Chris Foley
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Re: TV as an Oscilloscope

Post by Chris Foley » Sun Dec 21, 2003 5:12 pm

Dean is right. It sounds like the 475/475A is your best bet. Much better than the newer 2465, which has some parts availability/obsolescence issues. Good hunting.<p>Chris

Michael-love-electronics
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Re: TV as an Oscilloscope

Post by Michael-love-electronics » Mon Dec 22, 2003 2:23 pm

Dear Chris, Dean,...<p> Thanks very much for your consideration, I really appreciate that. :) :) :) :)

samsmiles
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Re: TV as an Oscilloscope

Post by samsmiles » Mon Dec 22, 2003 5:38 pm

Michael did you check links I gave you?
Bruces article in circuit cellar gives you exact schematic how to build it. Paper costs $ 1.15.
check it out. Schem. is free for download.
good luck with it its simple to build.
Sam
PS but as said before it doesn't do 100 MHz<p>[ December 22, 2003: Message edited by: Sam Smiles ]</p>

chessman
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Re: TV as an Oscilloscope

Post by chessman » Sat Jan 03, 2004 10:24 am

Michael - look at the links above.

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