Radio Transmitter and receiver

Discussion in 'Wireless & RF Design' started by Robin Mitchell, Jun 19, 2011.

  1. Robin Mitchell

    Thread Starter Well-Known Member

    Oct 25, 2009
    734
    200
    Hi everyone

    I have looked in a lot of places but cant find what i want

    I want to make a radio transmitter and receiver that operates bellow normal radio stations (FM 80Mhz to 108Mhz). So inother words a transmitter that sends radio waves on 40 to 70 Mhz

    How can i do this. Do i use a larger variable capacitor next to the coil or make the coil bigger?? Are there formula to calculate the frequencies?

    Many thanks,
    Robin
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    Beware that you use frequencies that are allowed.
    Otherwise you will get in trouble with the local telecom authority.
    In holland (where I live), when they catch you with an illegal transmitter, you loose the transmitter and everything that is connected to it.
    Also you will get a fine of upto 1200 euro over here.

    So look-up the available frequencies and the allowed powers.

    Bertus
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    This is why I have a technicians license in amateur radio (aka HAM). It allows me to build a transmitter and receiver with power on several frequencies. The spectrum is sliced up into chunks, not all are available for public use. If you think they can't find you if you are out of bounds, think again. It is a precision science, and has been since WWII.
     
  4. Robin Mitchell

    Thread Starter Well-Known Member

    Oct 25, 2009
    734
    200
    None of these replies are answering my question. I know you only want me to be kept out of trouble and i appreciate that :D but i just really want to know about making a radio work on a very very low frequency (ones that no one uses :p )

    thanks
     
  5. PatM

    Active Member

    Dec 31, 2010
    81
    72
    The frequencies you mention ( 40 to 70 Mhz), are not very very low frequencies.
    They are located between HF and VHF.
    These frequencies are used by many commercial licensed operators.
    I for one would not help anyone who wants to operate illegally.
    A amateur license is not that difficult to obtain, and will keep you out of trouble.
     
  6. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    In Holland the the telecom authority seem very strict but working with small power TX should not create any hazard......
     
  7. Robin Mitchell

    Thread Starter Well-Known Member

    Oct 25, 2009
    734
    200
    i wanted to send "blips" over radio.
    Does anyone remember that crazy satellite circuit i designed ages ago with the 555 timers??
    Thats what i want to make :D!!
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    http://transition.fcc.gov/oet/spectrum/table/fcctable.pdf


    The 50-54MHz band is designated amateur.

    See page 19 of pdf

    See US81 page 135
    See US220 page 139

    Amateur bands are jealously guarded by amateur radio operators. Should your transmission be received and you are unable to produce a station ID, the amateurs will gladly help any and all government(FCC) officials find you/hunt you down like a dog.

    You have been warned!

    Get a license and operate legally. Don't be an ATM for the government Tax collectors and a source of financial enrichment for our criminal justice system.
     
  9. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
  10. PeeSeeBee

    Member

    Jun 17, 2011
    43
    7
    The formula for a resonant LC circuit is:-

    f = 1/(2 X pi X √(LC)) where L= inductance in Henries & C = capacitance in Farads.

    So the higher the capacitance or inductance, the lower the frequency.

    If you are winding your own coil, the formula for a single layer inductor is:-

    L (uH) = r^2 X n^2 / (9 X r + 10 X l) where:-
    r = coil radius in inches
    l = coil length in inches
    n = number of turns
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    For those individuals with more good money and good reputation than they know what to do with, and feel the God given right to squander it by rendering it unto Cesear and His Minions, by all means, render away.

    For the rest of you with more sense and who seek knowledge before rashness.


    GET A LICENSE to transmit and be done with the problem
     
  12. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    Buy a copy of "The Radio Amateur's Handbook" it will have everything you'd want to know about 6 meter radio equipment. Even a less expensive old used book would work.
    I thought that if you stayed under 100mw you could do whatever you want.
     
  13. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,792
    948
    If its on one of those freq's that they use to spy on ET, then, be ready for a visit from the men in black. :)
     
  14. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I anticipated that I might want to do something like this someday, which is why I got the license. It isn't that hard, and if you look up the Hams in your area you will find a community that is more than willing to get you there. After you are legal you will find further help with the technical details.

    It isn't a coincidence that many of the people on this site are Hams.

    You will also notice there is a forum just for this type of question already.

    Radio and Communications

    I am willing to bet more than half the people responding to this thread already have their licenses.
     
  15. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello Bill,

    You are probably right.
    I have my licence for more than 30 years, so I want to keep things straight.

    A copy of one of the large amateur radio groups books will give you a lot of information.
    For the US there is the ARRL
    For the UK there is the RSGB

    You can also take a look in the RF related links thet I posted some time ago.

    Bertus
     
  16. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    Nice link...........
     
  17. radiohead

    Active Member

    May 28, 2009
    474
    31
    the fewer the turns in the air coil, the higher the frequency. The more turns, the lower the frequency. Breadboard your circuit and if you have access to a spectrum analyzer, that will help you find the center frequency much easier. You could also make a crystal controlled frequency transmitter at a set frequency so it won't drift.
     
  18. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Last edited: Jun 21, 2011
  19. Mulonde

    New Member

    Jun 23, 2011
    1
    0
    Cheap man! Let me look for the Digram to help you
     
  20. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Did you mean diagram?
     
Loading...