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  1. #1
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    300 mhz bandpass filter circuit

    Hi all

    sorry about my bad english

    I want a circuit for no-pass UHF filter. for RF antenna T.V

    It must allow to pass VHF-L and VHF-H with high quality and not allow to pass UHF

    thank you for answer

    •   Alt7th December 2006, 00:29

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  2. #2
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    uhf filter

    It looks as if a low pass filter will work. You need to specify the following:

    source impedance
    load impedance
    frequency range in MHz that will be passed
    frequency range that will be attenuated
    the amount of attenuation in the attenuated frequency range.



  3. #3
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    uhf low pass filter

    use a vhf antenna

    and you wont have a problem

    as a properly designed n fed antenna will do this job for you

    as long as you use a balun or a balanced feeder



  4. #4
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    filter uhf tv design lc

    there are a hotel and they want to control the content of channel .

    there are 2 group of rooms , some rooms are allowed to watch VHF and some rooms allowed to watch VHF and UHF.

    the allowed room may be changed, one day may be 40% of rooms allowed and one day may be 80% of rooms allowed.

    hotel central ANT. for all room . ( Each room have 1 coaxial cabel)

    I want to build a circuit that :

    1- when circuit active , the user of room not able to watch UHF ( only can watch VHF)

    2- when circuit is not active , user can see VHF and UHF channels.

    thank you



    •   Alt7th December 2006, 18:14

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  5. #5
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    helical resonator low pass filter

    A 5th order low pass filter will do the job but you must specify which TV or channelization standard is in use in your country to get better answer. Are S channels used in this hotel?



    •   Alt7th December 2006, 19:02

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  6. #6
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    filtr low kill

    Quote Originally Posted by leilarazavi2000
    there are a hotel and they want to control the content of channel .

    there are 2 group of rooms , some rooms are allowed to watch VHF and some rooms allowed to watch VHF and UHF.

    the allowed room may be changed, one day may be 40% of rooms allowed and one day may be 80% of rooms allowed.

    hotel central ANT. for all room . ( Each room have 1 coaxial cabel)

    I want to build a circuit that :

    1- when circuit active , the user of room not able to watch UHF ( only can watch VHF)

    2- when circuit is not active , user can see VHF and UHF channels.

    thank you
    You need a simple low pass filter with one or two varactor diode. When varactor capacitance is high, the filter will kill the UHF and the poor customers will not be able to see the p*orn movies...



  7. #7
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    low pass filter uhf

    [/quote]

    You need a simple low pass filter with one or two varactor diode. When varactor capacitance is high, the filter will kill the UHF and the poor customers will not be able to see the p*orn movies...[/quote]

    Yes ...you right ,but this is not for p*orn movies.

    I need low pass filter to kill UHF band. <300 MHz

    who can give me the circuit for this low pass filter?



  8. #8
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    lc filtr uhf

    You can use filter solutions software to design low pass filters.(search google)



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    uhf band filter schematics

    You should use Helical low pass filter form at that frequency that is controlled by PIN diodes from remote current..



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    no-pass filter

    Quote Originally Posted by BigBoss
    You should use Helical low pass filter form at that frequency that is controlled by PIN diodes from remote current..
    May I use L C lumped circuit on pcb? Do the pcb trace affect the frequency
    response?



  11. #11
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    uhf pass filter

    @leilarazavi2000

    you can find free but still good filter design software here:

    http://tonnesoftware.com/

    Especially get friendly with Elsie, SVCfilter and Helical.

    When you have the low pass filter that blocks signals above 300MHz you can use a pin diode switch as BigBoss mentioned, see this link on pin diodes:

    http://www.microsemi.com/literature/pinhandbook.pdf

    and refer mainly to Figs 2.6 and 2.7 and of course you have combine the filters and the diodes into a common matching circuit for 75 Ohms impedance.

    If you feel like using a double amplifier optimised separately for VHF and UHF bands in an integrated circuit form with built-in switch for either band, see this link:

    http://www.vishay.com/docs/85171/85171.pdf a data sheet for Vishay's TSDF12830YS. Using this amplifier you can compensate for a bigger insertion loss due to your filters and cables.

    rgds, unkarc



  12. #12
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    low pass vhf filter

    Quote Originally Posted by hebu
    Quote Originally Posted by BigBoss
    You should use Helical low pass filter form at that frequency that is controlled by PIN diodes from remote current..
    May I use L C lumped circuit on pcb? Do the pcb trace affect the frequency
    response?
    Of course you can but a filter implemented with lumped elements will have lower qualty factor than helical resonators at that frequency due to high inductance and capacitance values.But obviously, if you use high quality components ( inductors,capacitors) that will also work but it doesn't give very sharp passing slope.

    In addition to, the pcb losses can be a trouble if you use low cost pcb material like FR3 or FR2..

    In fact, there are many methods to implement this kind of filter but all depending on cost and implementation technique.



  13. #13
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    active inductors filter for uhf pdf

    Quote Originally Posted by hebu
    May I use L C lumped circuit on pcb? Do the pcb trace affect the frequency
    response?
    Hi,

    Yes you may, if you include the surface area of pcb traces as capacitors into your filter design. Good quality double sided pcb is preferred of course, and you have to determine unit area/capacitance between the two sides of pcb. This technics is useful mainly for wideband filters.

    There is relatively strange approach for creating pcb (mainly high voltage) capacitors by placing differently sized rectangular pcb pieces onto a bigger pcb board, see an example: http://www.irational.org/sic/radio/frb-9pole-lpf.html
    Nevertheless, this approach needs some tinkering with the surface areas...

    rgds, unkarc



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