+ Post New Thread
Results 1 to 9 of 9
  1. #1
    Newbie level 2
    Points: 25, Level: 1

    Join Date
    Jul 2019
    Posts
    2
    Helped
    0 / 0
    Points
    25
    Level
    1

    Generating a frequncy

    Helo all.i need a circuit which can generate a frequency of 27Mhz having a pulse rate of 800 pulses per second."Pulse on duration" should 100 micro seconds.Any one have any idea about the implementation of cicuit?Antena size should be 8cm

    •   AltAdvertisement

        
       

  2. #2
    Super Moderator
    Points: 258,547, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,137
    Helped
    13722 / 13722
    Points
    258,547
    Level
    100

    Re: Generating a frequncy

    Have a 555 circuit generating the modulation waveform and a 27 MHz crystal oscillator enabled by the pulse signal. 8 cm is rather short for 11m wavelength, don't expect large antenna efficiency.


    1 members found this post helpful.

  3. #3
    Newbie level 2
    Points: 25, Level: 1

    Join Date
    Jul 2019
    Posts
    2
    Helped
    0 / 0
    Points
    25
    Level
    1

    Re: Generating a frequncy

    Any schematic?



  4. #4
    Advanced Member level 4
    Points: 6,247, Level: 18
    kripacharya's Avatar
    Join Date
    Dec 2012
    Location
    New Delhi
    Posts
    1,209
    Helped
    182 / 182
    Points
    6,247
    Level
    18

    Re: Generating a frequncy

    Quote Originally Posted by khan_Ali View Post
    Any schematic?
    I think you are confusing this forum with Google.



    •   AltAdvertisement

        
       

  5. #5
    Full Member level 3
    Points: 1,131, Level: 7

    Join Date
    Jan 2019
    Location
    Belgium
    Posts
    163
    Helped
    69 / 69
    Points
    1,131
    Level
    7

    Re: Generating a frequncy

    A modification of FvM's suggestion would be to use two 555 timers, one tuned to 27MHz and the other to 1/800 Hz and then do a logical AND of the two signals. At the beginning and towards the end of the pulse edges, you may get spikes. If that is not acceptable, then you need to do synchronization.



  6. #6
    Advanced Member level 4
    Points: 6,247, Level: 18
    kripacharya's Avatar
    Join Date
    Dec 2012
    Location
    New Delhi
    Posts
    1,209
    Helped
    182 / 182
    Points
    6,247
    Level
    18

    Re: Generating a frequncy

    Quote Originally Posted by vivekroy View Post
    A modification of FvM's suggestion would be to use two 555 timers, one tuned to 27MHz and the other to 1/800 Hz and then do a logical AND of the two signals. At the beginning and towards the end of the pulse edges, you may get spikes. If that is not acceptable, then you need to do synchronization.


    Why didn't I think of that ?
    Oh yeah... Because it is not feasible.



  7. #7
    Full Member level 3
    Points: 1,131, Level: 7

    Join Date
    Jan 2019
    Location
    Belgium
    Posts
    163
    Helped
    69 / 69
    Points
    1,131
    Level
    7

    Re: Generating a frequncy

    Yes. I had forgotten the maximum range was around 5MHz. By bad.


    1 members found this post helpful.

    •   AltAdvertisement

        
       

  8. #8
    Super Moderator
    Points: 258,547, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    45,137
    Helped
    13722 / 13722
    Points
    258,547
    Level
    100

    Re: Generating a frequncy

    555 datasheet has application circuits and formulas for pulse width and frequency calculation.

    As for the 27 MHz generation, I was expecting a frequency stable sine oscillator (e.g. crystal based) because a radio transmitter has legal requirements for frequency stability and low harmonics.


    1 members found this post helpful.

  9. #9
    Super Moderator
    Points: 80,586, Level: 69
    Achievements:
    7 years registered
    Awards:
    2nd Helpful Member
    betwixt's Avatar
    Join Date
    Jul 2009
    Location
    Aberdyfi, West Wales, UK
    Posts
    13,205
    Helped
    4410 / 4410
    Points
    80,586
    Level
    69

    Re: Generating a frequncy

    27MHz crystal osc, NE555 or similar to produce the pulses, use the pulses to bias the 27MHz oscillator. That's how almost all ASK transmitters work.

    For the antenna - it depends whether any special radiation patterns are needed but the only practical way of squeezing 11m of wavelength into 8cm is to use a tightly coiled helical antenna. Given the small size, it wouldn't be very efficient but it would work.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


    1 members found this post helpful.

--[[ ]]--