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1. What specifications are req. for good Video(Audio also) transmitters?

low distortion, low noise, wide bandwidth.

2. Can we use fm transmission for remote controlling switches(just ON and OFF)? How?

Yes. Use an FM transmitter and an FM receiver. The receiver can simply detect any modulation or can detect a certain tone frequency that has modulated the FM carrier frequency.
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A video transmitter block diagram is shown in Google, in Howstuffworks and in many other websites.
For TV, a video transmitter is an AM transmitter with a mixer to mix the sync pulses with the wideband analog video. Colour TV is a little more complicated since there are a few completely different ways that are used around the world.

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Receiver?? how?? how can i use it to operate as a switch(for eg. to switch on a transmitter(video tx for suppose) placed somewhere at a distance where my transmitting pulses(for switching purpose)  can reach  that can switch the second transmitter(video tx or ....) )

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Range is not a big issue....it can be small to remain in the limits...... but what i want is to operate my tx (for suppose if I make a video tx..and it is put somewhere not far from my house or can be in my house...if range is realy serious!! I will want to switch on that tx by sitting in front of my tv....just what I am trying to do is to combine  a remote switch and  a video or audio tx......Can u guide me on this....

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The transmitter FM modulates a silent carrier since without the carrier there is a lot of noise and when receiving the unmodulated carrier there is silence.
The audio circuit works and activates the beeper when there is or is not any noise. The radio receiver circuit isn't shown so we don't know all the details.

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I searched for video tx and found many.... But I'm unable to decide which one is better and why.... I've attached one of them....... I really don't know how to judge... Perhaps, you can help me.... Please give me some tips .......

How can I combine my audio and video outputs from VCR to connect to this crkt(my guess ...from poptronix???)

Is this crkt not better than poptronix?.....this crkt uses crystal accuracy ...Isn't it?

post-19161-14279142857804_thumb.png

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Hi MNA!

These schematics you uploaded are not the easiest to build I would say, to build them you need some "extra" skills in RF technique.
Since the range is not an big issue why not use a RF-modulator from a scrap video then you have both audio and video transmitter or build your own:
http://www.web-ee.com/Schematics/RF_Modulator/rf_modulator.htm

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Skills!!!! I'm a beginner....
I don't know the theory behind these much....
I'm unable to understand that RF Modulator....If u could tell me furthur, it will help me a lot.....
What about the poptronix crkt? .....
Thanx

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Well. the poptronix circuit... just forget it.
You can find an RF-modulator in almost every video player, it's a small box with 4-6 pins, there is inputs for both composite video and audio and a pin for supply voltage.
If you look at the rear of a video you'll see it, it's where the antenna connector is.

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Sorry Sir,but I'm still unable  to understand what u r saying....
what's the connection of an RF modulator with video tx.... ???
How could i send my video output from my VCR to my TV without any connection b/w the two????????

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As I told you if range is not an big issue  ;D
Just connect a short piece of wire to the center pin of the output connector of the RF-modulator and a short piece of wire into the antenna connector of the Tv-set, if the distance between your tv and video player isn't to far you will se the video sent by the video player on the tv screen. You'll have to put your tv on same channel as the RF-Modulator otherwise you wont see anything.
Forgot to mention, the two wires act as antennas.

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Of course Sir, I said in my previous posts that range is not a big issue..... But I said that  for remote switch (i.e. for switching ON or OFF my tv tx through a remote or u can say some another tx........That was only a design idea .....I'm not an expert.... )..... TV tx should have a good range but I'm ineterested in better quality than range....but range will be a bonus....
The simplicity of RF Modulator gives me an idea that it's range will be very short....I don't know how much....
The web-ee modulator contains only 1 input for video..... ?

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You are right MNA that circuit is only for video.
The link gogo2520 posted show how a RF-Modulator is built, as you see there is input for video and audio.
To boost the signal from a RF-Modulator which is usually in the range 60-80dBmV a antenna preamplifier can be used or build an small RF-amplifier that cover a bandwidth of at least 8 Mhz for the UHF channel in use, it has to be broadbanded.
The quality you get is same as you get from your video, when it comes to remote do you mean those units you can buy that both transmit video/audio and let you switch channel on another tv-set?

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Thanx Gogo,SM2GXN.
Remote,,,, just to switch on or off my tv tx placed somewhere at a distance......
Well,I think it is better for me to concentrate on the tv tx than remote b/c without tv tx  what's the purpose of remote  ;D ;D  .....
You said,"Well. the poptronix circuit... just forget it."
ok I will forget it but only one last question about that.....ISn't the poptronix crkt and this avsender posted by Gogo doing the same thing ? .......why r u sayng me to forget it? ..... Is there anything wrong in the circuit ? .... I became curious with yr advice of forgetting it......
Thanx.

post-19161-14279142860508_thumb.jpg

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Hi MNA!

No there is nothing wrong with poptronix wireless link my friend  :) it's just that it is very high frequency 1250Mhz, firstly there is no PCB (printed circuit board) layout which is very critical at high frequencies, it's a matter of less than mm accuracy, well maybe not that much in this circuit but some RF experience is needed, for the 2nd you have to make an antenna which is not that hard but if you want to go by the book it is.
For the third you have to make a receiver for 24cm/1250Mhz and either down convert to the UHF band or demodulate the signal in order to get your audio and video out.
That's why I say forget it  ;D
Hope this satisfy your curiosity MNA

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