Reversing Polarity On a Television...?

I would like to first start off saying I am not really sure where I should be posting this. I hope it will be fine here. Okay, now to the fun stuff!

---
A few days ago while here at work, I was told by a co-worker he heard from a cornel in the army that if one was to reverse the polarity on a television set it possibly would become a sort of camera. A TV recieves a signal and outputs it to the screen. Once the polarity is reversed it then would be sending a signal back. Now this is where it gets strange. While the polarity is reversed your screen supossidly becomes the camera lense. Now the reciver of the signal can see through your TV set.

I had never heard anything like this before and I am not sure what to think. When I think "reversing" the TV set.. Okay. Cool. Why couldn't be done. What get's me is how can a screen do the actuall "seeing"? I would think that for this to happen you would need to hook up a camera for the "eye". I then begain to think about a camera. Is not a camera mearly a tube and a lense? The same as a TV?

Somewhere in a television there is a solid state relay. (So I hear) - (this is older info, now it may very well be a chip or even digital data encoded into the chip bios with todays modern technology) The solid state reley mighy have been/be a sort of remote control to start back-feeding the signal back to the "source".

I would now like to let you all know that I am not saying I beleive this nor am I someone who really get's into government conspericies. I am just wanting to find out if any of you here have heard of this. I would also like to discuss this further in depth. I mean, if you think it will not work.. Let's talk about how we could make it work. If you do think it is true/possible.. How?

Thank you all for your time and please forgive my spelling!

If you reverse the polarity of your tv set you would in effect cancel the signal and that is that.
You could also run the risk of blowing up your telly. I can pretty much guarantee you that you
telly will not turn into a camera lense. Another urban legend that is all.
Cheers big ears!

Would you mind giving a little more detail?

er..it's crap...you TV has a Rectifier to turn AC power to DC power....thus, reversing it, would have no effect. YOur TV has an Electrongun on the inside that shoots electrons at three diff kinds of material (Can't remember the name), these light up. reversing the polarity, would not turn the electron gun into a reciver, because an electron gun is inshort, a bunch of wire and a metal plate....oh well....hope this helps

- Noia

Here goes more detail, think of it as taking the toal opposite of something and smashing it together with it's opposite. You would get nothing for they cancel each other out. If this does
not explain it then think of modulo two addition.

Okay I do understand what you both are saying.

Forgetting the whole screen to cam idea... Now, why couldn't the chip (or whatever) send back signals? This part is very possible I would think. ?

Because the semi-conductors (and other components) blocks the current from going the other way.

The membrane (the flat thing you watch to and gives light in special circumstances) won't shoot fotons or electrons or whatever. It's like superman shooting laserbeams out of his eyes. I can tell you pretty sure that ain't gonna happen by switching polarity anywere in yer television. And even if you'd succeed you'd have another 1000 practical problems to overcome to record the stuff in any way.

What you are now talking about is a transceiver. Your television is a "receiver" ie: will only receive and decode signals. It will not send them out.

hmmmmm .. the story is a load of BS.. reverse the polarity will certainly cancell the signals.. it will also let out all of the smoke...

Now down to fact.. The reciever in your TV or any radio frequency recieving device has an ocillator (local Osc).. this signal can and does "leak" back out of the unit sometimes into the antenna.. this signal can be recieved upto 300m (1000ft) from the set.. this generally contains no usable information... it is of use to various departments to determin what TV, Radio channels are being recieved in a given area.. hmm very interesting signal profile from radio frequency scanners.. hmm should this person be listening to the Mobile phones???
So yes Yor tv can be a transmitter.. But certainly not by reversing the polarity...
can it be used to transmit information... yes.. but various electrical modifications are required..

As for the "Chips" sending back information.. well that won't happen by reversing any polarity.. end of story.. The signal paths are set and will not reverse.. You have the signal input, and outputs.. the path can not be reversed.. As I said earlier.. only "signal leakage" is the only way out for signals in a TV..

Can you use the TV picture tube to capture pictures....Hmm I remember a Joke Powerpoint file doing the rounds a few years ago.. that purported to capture images of the operator from the computer screen.. the final frame gave the real story..


Cheers

Und3ertak3r, Thank you. That is the sorta info I was looking for. :)

In a more security focused vein, it's interesting to note here that the signal "leaks" that Und3ertak3r speaks of are not the only leaks coming from your TV. Your TV also emits electromagnetic radiation which can be captured and translated using special equipment. The theory dates back to the 1950's when the military was concerned about electomagnetic radiation leakage and how to prevent it (the project was eventually named TEMPEST for Transient Electromagnetic Pulse Emanation Standard), but it was Dr. Wim van Eck who first theorized a practical way to harness and decipher these emanations into usable information. It is now possible to recreate the images displayed on computer monitors and television sets from a limited distance away. In this way, a television could be called a "transmitter" of EM radiation. Then again, by this standard, you could also call your blender, fax machine, photo-copier, and hair dryer "transmitters". :bigsmile:

the thing has a cathode ray tube, this is what shoots the electrons and this cant be reversed

"Your TV also emits electromagnetic radiation which can be captured and translated using special equipment."

So technically, this could also be used on a computer monitor. But one question. This equipment that captures this radiation, is it capturing bits and pieces, or is it capturing a continuous flow? In simple terms, would they see a "screen shot" or "live continuous coverage"?

Does this mean I can't use my digital camera as a projecter??
Damn. ;)

thanks roswell1329

Quote:

---

Your TV also emits electromagnetic radiation which can be captured and translated using special equipment.

---

now that I had missed.. thanks for the info.. more research for me..

Cheers

Good to see some good info comming out of my post!

He propably meant the polarity on the CRT ( Cathode Ray Tube ) well to bad.. it just wouldn't work..

read some more before comming up with stupid ideas !!

http://electronics.howstuffworks.com/tv.htm

You know I have often wondered about measuring the Anode current on a tv pix tube, amplifing it and subtracting the incoming video from it.. and see what sort of image would result.. theory.. the phosphor on the inside front of the tube is excited by the electrons and releases photons, incoming photons Could have an effect on the generation of mor photons and therfore increase the Current progressing to the Anode of the Pix tube..

yes I know it sounds hairbrained..

Certainly easier to use a speaker as a microphone.. but certainly not while it is being used as a speaker..


Cheers

Not quite...

To the best of my knowledge, early TV cameras (before the invention of CCDs) used CRTs to produce the signal. Essentially it's like a television, but backwards. The CRT is scanned just like a TV, but the amount of light falling on a given part affects the current, this current change is then amplified, modulated etc, and transmitted.

However, an unmodified TV would definitely not do this

1. It probably isn't the right sort of CRT. A colour one wouldn't work for starters.
2. It has no lens, so at best it would only be able to tell how bright your room was

So theoretically if you modified a small black-and-white telly a bit, stuck an absolutely huge lens on the front (a good distance from the screen) and hooked it up to the appropriate electronics, you could make it into a camera.

All this was superceded by the invention of the CCD, a chip which produces electrical signals based on the light falling on it. This lead to the invention of video cameras, and TV cameras adopted them once the quality became good enough. These days they're so good that digital stills cameras can compete with professional-quality film. Also opened up the door for tiny (1cm cube or less) cameras used for security, espionage and gimmicks in mobile phones.

True the Vidicons used a different type of phosphour.. a photo electric reactive type.. my theory on that is now a bit rusty....

I challenge though..

Quote:

---

All this was superceded by the invention of the CCD, ...... This lead to the invention of video cameras, and TV cameras adopted them once the quality became good enough.

---

Video cameras (that is home/domestic) using Vidicon/plumbicon tubes were around long b4 CCD's and certainly CCD's allowed the domestic video camera to reach the pocket of joe average.. CCD's made adifferance as Domestic Video Cameras started to go mainstream..

Quote:

---

So theoretically if you modified a small black-and-white telly a bit, stuck an absolutely huge lens on the front (a good distance from the screen) and hooked it up to the appropriate electronics, you could make it into a camera.

---

kill joy... but you are correct.. there is another problem.. the EHT in a television is (and worse in the newer sets) horrificly noisey/unstable this would make such an idea almost unworkable.
but it was just a thought..


Cheers

signal leakage is how the TV licencing authority in the UK catch people without a licence in this country they pick it up with a reciever, then send you a big fine.

VEry true jinxy,

It is also how the same authority's are able to tell if you have recieving equipment listening to the wrong stations.. ie mobile phones, cordless phones.. radio scanners have very distinctive signatures.. hmm
I wonder what the leakage profile/signature of 802.11x receivering equipment is like? a methode to tell if some one is sniffing your 802.11 network..
Hey this thread has bounced into the realm of computer security..


Cheers