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  1. #21
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    Re: TV transmitter connection with antena....

    Quote Originally Posted by BigBoss View Post
    I have designed a VCO with avaricap for tuning from 175MHz-203MHz.It's quite low noise oscillator and stable in simulation.
    If you would , I can post schematic here.It would be a practical experience for you.

    Hey, it would be great, please post the schematic if you can! Can you explain also how would I use that?

    I certainly did not give up.

    I have tried again with modified schematic (BC547):

    this is from this video:
    https://www.youtube.com/watch?v=Qrbb5TgZUi8
    this guy has removed few parts, including DIODE and capacitor from the schematic from first post and still had a good quality with 5V supply....

    I tested it, it seems to give a slightly better results, but the screen is still tearing or very not readable.



    •   Alt23rd June 2017, 14:08

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  2. #22
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    Re: TV transmitter connection with antena....

    Quote Originally Posted by Garyl View Post
    Hey, it would be great, please post the schematic if you can! Can you explain also how would I use that?
    OK,here is the schematic.It's working in simulation only, I have never tested on a board.
    Vtune can be between 3V-10V.Use SMD components as possible.A carefully designed PCB with 2 layers with proper GND layer will help you much.
    The VCO works between 175-203MHz with a pretty good Phase Noise.Output level is around 1.2-7.5dBm, Video Input can be as same as in your previous circuit schematic.
    Don't apply too high video signal and not change 100 Ohm emitter variable resistor.( Use multi-turn high quality SMD variable resistor/trimpot )
    GA3094AL: Coilcraft Air Cored Inductor(SMD)
    BB689:Varicap Diode (SMD)
    BFR193F:BJT (SMD)

    Click image for larger version. 

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    Last edited by BigBoss; 23rd June 2017 at 16:21.



    •   Alt23rd June 2017, 16:05

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  3. #23
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    Re: TV transmitter connection with antena....

    Thanks, what kind of software are you using to simulate this circuit?
    Also, if you're designing it, can you design it for 500 MHz or so? It seems that most of the old TVs here are on such frequencies....

    I'm afraid I will have toruble getting a varicap for that..



    •   Alt23rd June 2017, 21:23

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  4. #24
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    Re: TV transmitter connection with antena....

    Quote Originally Posted by Garyl View Post
    Thanks, what kind of software are you using to simulate this circuit?
    Also, if you're designing it, can you design it for 500 MHz or so? It seems that most of the old TVs here are on such frequencies....

    I'm afraid I will have toruble getting a varicap for that..
    I'm using AWR Microwave Office.I can design also 500 MHz, no problem.
    The varicap is BB689 of Infineon.( it's still available otherwise use an equivalent)



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