I need you to check my project diagram

[jordan_bilal]

hi,
I have choose a project through internet, but I am not sure if it works properly.
i have alot of questions on it .....
any one can help i appreciate

 

[Grossel]

i have alot of questions on it .....

How do you image somebody can help when you haven't asked any questions yet?

I can almost smell trolling around

 

[Nopy]

Just ask and we may help u jordan

 

[jordan_bilal]

Just ask and we may help u jordan

well ... thanx for reply
1st question is .... this circuit suppose to work as video sender, but after i made a search about the concept of video sender (it must send the audio signal by FM modulation, and the video signal by AM modulation (vestigial sideband) )
so the question is where the FM modulation in the circuit ..
and what happend to the video signal after that diod and why did we use it ????

 

[JimB]

Well, it will transmit the video as AM, but not as VSB but as double sideband with full carrier.
The carrier frequency is intended to be low VHF (50Mhz) by the look of the lowpass filter feeding the antenna.

As for the audio, who knows?
The audio does not make sense to me, and there is certainly no intentional FM modulator in there.

JimB

 

[jordan_bilal]

well .... so its not VSB so what is the function of the last filter ... and ya about the AM modulator, where it is ????
any way ... there is a similar circuit but with transformer ....
maybe it can help u to understand what happend to the audio signal....
thanx 4 ur time

 

[JimB]

so its not VSB so what is the function of the last filter?

The filter comprising L1, C12 and C13 is there to filter out the harmonics of the carrier.
Assuming the carrier is at 50 Mhz, there will be harmonics at 100, 150, 200, 250, 300Mhz etc. That filter suppresses those harmonics.

and ya about the AM modulator, where it is ????

Transistors Q5 and Q6 provide a "power amplifier" function, Transistor Q1 effectively controls the collector voltage for Q5 and Q6 creating an amplitude modulator.
The RF output power being (roughly) proportional to the collector voltage.

there is a similar circuit but with transformer ....
maybe it can help u to understand what happend to the audio signal....

Not just "a similar circuit with a transformer", but a circuit with an oscillator which is frequency modulated by the audio. The original circuit just had a bunch of components which did nothing in particular.
This oscillator (Q3 and T1) will be running at whatever frequency (around 5Mhz at a guess) and the output of the oscillator is link coupled by the secondary winding of T1 into the amplitude modulator.

So the resulting output from the antenna will be the carrier frequency (50Mhz), amplitude modulated by:
the video
the audio subcarrier at 5Mhz, which is in turn frequency modulated by the audio.

I have extracted the correct circuit diagram from the Word file so that others can see it easily.

JimB

 

[jordan_bilal]

so its using AM DSBLC not a VSB, but as i told u that i read alot of topics talks about tv trnsmitting that it using VSB ....
any way if u have another circuit doing the same job please send it to me.
or if u can show me more detail about this circuit
(i mean if u can write down what happened with the signal since it enter the circuit until its radiated on antenna)
i really appreciate ur efforts

 

[audioguru]

Old fashioned broadcasted TV used VSB to reduce the bandwidth. The video was AM modulated and the audio was FM modulated.
Why are you making an old fashioned TV transmitter? Today TV is digital high resolution. Make a 3D digital high resolution TV transmitter instead.

 

[jordan_bilal]

well... i will be grateful if send me such thing.
but in fact i have to finish what did i begin because i have to see my Dr. tomorrow ... so if u please give more detail about this circuit first
(why did we use the calmper at the begining, and if Q1 used to make AM mod. where he take the high frequency to modulate it depends on msg signal, and what is the function of L3 and Q2 ?, and did we send the hole signal at last on the same carrier (which comes from colpits oscillator).
detail please