hey

Discussion in 'The Projects Forum' started by peter_morley, May 17, 2011.

  1. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    If i am transmitting a low power I shouldn't be bothering anyone all I am trying to do is understand how these circuits work.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    That really depends on the frequency and method of generating it. A wide spectrum with lots of harmonic peaks could wreak havoc on people or equipment you have no idea about, at frequencies which you did not intend to be transmitting in.

    Be more specific, so WE can be more specific in our answer.
     
  3. Kermit2

    AAC Fanatic!

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  4. CDRIVE

    Senior Member

    Jul 1, 2008
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    This post wouldn't make any sense to anyone unless they happened to have read your last topic. You know... the one that the Mods closed.
    http://forum.allaboutcircuits.com/showthread.php?p=363290#post363290

    A 555 will not work as an RF Transmitter. It will function as a HARMONIC GENERATOR!
     
  5. simo_x

    Member

    Dec 23, 2010
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    Also, as I know you can not transmit on every frequency you would like to. For example, just to use a citizen band equipment which works between 25 & 28MHz, you have to obtain some permission.

    If you are interested in RF theory & circuits, I strongly suggest to study on some book related to the topic. Knowledge about oscillators, filters and so on, is off course needed, and as some experienced members have already told you, it's better you forget about 555.

    If you have already some evaluable knowledge in electronics, you can start from this book
    [​IMG]
     
    Last edited: May 17, 2011
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    Things must have changed. What happened to the radio amateur's code?
    Though shalt not cause radio interference.
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I'm not worried about some unlicensed hobbyist working with a very low power rig that's probably legal, especially when I'm aware of flagrant violators intentionally causing interference with big antennas and powerful transmitters yet eliciting little or no FCC enforcement action.

    Experiment kits like this one http://manuals.elenco.com/manuals/ep-50.pdf have included broadcast band transmitters (#39) for over 50 years with no serious ill effect.
     
    Last edited: May 18, 2011
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    I will reiterate, yet again... A 555 is not a broadcast band or any other band transmitter of any kind. The very first thing that I learned, as a novice ham, was to transmit the cleanest signal possible. A 555, as a signal source, is the antithesis of this! If he does get it to work he won't have to tune the receiver to hear it because it will be scattered all over the spectrum!

    Perhaps you'd like to post the Amateur Radio Handbook page that describes a 555 based transmitter?

    FYI.. The fact that the FCC lacks the resources to track down every idiot, mindlessly playing with the radio spectrum, doesn't make it right. :mad:
     
  10. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    can someone close this thread
     
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Who knew the humble 555 could be used as a broad-spectrum jammer. :rolleyes:

    If the signal gets a μV past the end of his arm and is DC to daylight wide as you fear; his neighbors, the local police, all the local radio and TV companies, carloads of ham radio operators, CBers, tow truck and cab drivers, the NSA, FBI, state police, NASA, the cell phone companies, all the utility companies, every branch of the military, the FAA, the railroads, little kids with toy walkie talkies and the FCC will descend on him like a lynch mob. :eek:
     
  12. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    CDDrive I understand your concern but please don't call me an idiot for being intellectually curious. You were an "idiot" once when you didn't know how these things worked. I thought I would be getting encouragement about this as long as I was only using a small wire as an antenna. Plenty of people make am transmitters that are low power so they don't interfere with the commercial signals. I believe I am not wrong about this.......argument ensues;)
     
  13. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    If you don't ask, you won't learn. If you don't listen, you still won't learn.

    There was more than one response saying this was a very bad idea.

    Now if you want some good ideas, ask.

    I've let my HAM license laps, but I still have the ethic. Any experienced Ham does not like circuits that splatter over the RF spectrum, and a square wave such as the 555 produces will splatter badly. BTW, I'm considered one of the experts for 555's around here.

    Bill's Index

    There are many simple single transistor circuits out there that will do what you want, cleanly. They are simple and cheap.

    When I was a young teen (with out any formal school, nor was their internet or computers) I methodically went down a list of text book schematics and made every oscillator I could. Text book examples rarely work as advertised, and I'm sure I did my share of splatter (though I was trying for clean). We lived in deep country with weak TV reception, my Dad's reaction when his TV started showing herring bone interference (or weird sounds) was "Turn it off.". It worked most of the time too.

    You have the resources to go down the same path with much more help. Pick a project with a definite goal, and we'll get you there.

    BTW, we have forum specifically for RF projects...

    Radio and Communications
     
  14. peter_morley

    Thread Starter Member

    Mar 12, 2011
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    So why does a square wave splatter all over the place? I understand the square wave for the 555 timer produces only a high and a low (not a negative). So the sine wave produces a gradual shift from positive to negative. Tell me if i am wrong.
    BTW I'm a 666 expert. ;)
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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  16. Adjuster

    Well-Known Member

    Dec 26, 2010
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    A sine wave of constant amplitude and frequency contains energy at that frequency only. If modulation is applied to that sine wave then further frequencies called sidebands will be developed, but always related to the basic carrier frequency.

    Waveforms other than sinusoidal contain higher (harmonic) frequencies which are multiples of the basic or fundamental frequency. Square waves are particularly rich in harmonics, containing odd multiples of the fundamental- see this link: http://www.allaboutcircuits.com/vol_2/chpt_7/2.html

    If we then apply modulation to a square wave "carrier", as well as the intended fundamental frequency and associated modulation sidebands, all the harmonics can behave like carriers, each with their own set of sidebands. The whole lovely mess can be radiated to a greater or lesser degree, depending on the response of the antenna. Net result? Horrible interference, and grumpy old radio hams (or cops, maybe) coming to sort you out.
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    A sine wave is a fundamental wave form, maybe the fundamental waveform. It is a frequency at it's purest. Any other shape has other frequencies, usually multiples of the fundamental frequency, called harmonics. A harmonic is an integer multiple of the fundamental frequency.

    A square wave has the most harmonics of any wave form out there.

    Their is a special brand of calculus that covers this, it is called fourier analysis
     
  18. CDRIVE

    Senior Member

    Jul 1, 2008
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    I didn't call you an idiot, it was a generalized statement. There have been many informative posts since you posted this and you are hopefully (now) grasping why the 555 (square wave generator) is not suitable for radio applications. On the other hand, if you ignore this information then you will be putting yourself (voluntarily) in that category. ;)
     
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