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1MHz amplifier

  1. Jan 30, 2008 #1
    i designed an crystal oscillator of 1MHz using MC14069 ic and now i need the design of a power amplifier circuit to increase the power of the 1MHz carrier wave...can somebody help me with this!!!
     
    Last edited by a moderator: Jan 31, 2008
  2. jcsd
  3. Jan 31, 2008 #2

    f95toli

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    How much power do you need? And what is the impedance of the load?
    1 MHz is not a very high frequency, so you might ven be able to use a simple op amp circuit.
     
  4. Jan 31, 2008 #3

    berkeman

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    Also, what are you going to do with this 1MHz "carrier" wave? Keep in mind that 1MHz is right in the middle of the commercial AM broadcast radio band (at least in the US), so you can't let much of your signal leak out of your lab. You sure as heck can't be driving an antenna with the signal....
     
  5. Jan 31, 2008 #4
    the transmitter should have enough power so that the signals should be received anywhere within the range of 10 metres... just wanna try receiving it ...put some sckottky rectifier diode and capacitors to make an led glow.
     
    Last edited by a moderator: Jan 31, 2008
  6. Jan 31, 2008 #5

    berkeman

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    For a 10m range, you only need to transmit microwatts for an AM receiver to pick it up. You will absolutely not be able to just use a passive AM receiver with a rectifier to make an LED glow. The level of power required for that is WAY over the allowed power levels for transmitting in the licensed AM broadcast band.

    That is a bad experiment to try, unless you happen to have access to a large anechoic chamber where you can transmit all you want, since the signal cannot make it out of that shielded chamber.

    Instead, consider building a simple low-power FM radio transmitter kit. You can get them from Radio Shack or online like here:

    http://www.transeltech.com/kits/kits1.html

    The power output from these hobby kits is very low, low enough to meet FCC regulations, and the range is about the 10m that you are looking for. You use a regular FM radio receiver to pick up the signal.
     
    Last edited: Jan 31, 2008
  7. Jan 31, 2008 #6

    drv

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    The above answer does not solve the original problem, since the FM radio is in a much higher frequency band.

    Not an easy problem to solve for the 1 Mhz frequency. You will need two antennas: a transmitting antenna and a receiving antenna. Both of them will be a small fraction of a wavelength, so the signal power will fall off to the sixth power with range, and you will not have to worry about FCC regulations unless you transmit large amounts of power. In order to do this, your best choice is to transmit pulses at a low duty rate. Your LED will blink, which may suit your requirement.

    Help is here if you need it.
     
  8. Jan 31, 2008 #7

    berkeman

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    What you are suggesting is illegal and irresponsible. Please do not encourage hack experiments with the radio spectrum.
     
  9. Jan 31, 2008 #8

    drv

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    What is a "hack experiment"?

    The FCC regulations require that the radio emissions must be below stated levels. It is very difficult to get above these levels in the AM band for small antennas, especiailly for the pulse modulation method that I recommended. In addition, peak pulse transmission levels are not specified (this is called "spread spectrum"). Only the average transmitted power is limited. It is easy to test for interference by tuning an AM receiver to the transmitted frequency. If we are talking about transmitting Watts of power and above, then you are most likley quite correct.

    However, I do agree that anyone experimenting with electromagnetic radiation should be familiar with the FCC regulations. Interference with normal radio reception is restricted. The same rules also apply to FM transmissions, which was one of the earlier recommendations. These higher frequency bands are much more likely to cause illegal interference. Perhaps you should comment to their quote in the same way, since that method is much more likely to cause problems.
     
  10. Jan 31, 2008 #9

    berkeman

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    I was worried that your short comments would not be interpreted correctly by the OP (who abviously does not have much RF experience yet), and he would run off and do something that would generate harmful interference. I could just see him trying to do non-pulse-shaped pulse modulation, and stepping all over nearby broadcast receivers (even higher frequency ones). I honestly do not know what the power limits would be for spread spectrum transmissions in the broadcast AM band, and if they are different from unintentional radiator limits. But seeing as the OP's original request was to passively light an LED with the fields.... Maybe we could just have him use inductive power transfer at 1MHz? Then as you say, the antenna (the coil) would be small enough to have basically zero radiation resistance.

    I've just had way too many problems with harmful interference in my work with HAM radio. At first I thought transmitter hunts (www.thunt.org) were just fun practice. But now I know that they are definite necessities to keep the emergency communication networks operational. Sorry if I came across kind of heavy-handed in my reply. Interference with licensed communication is not fun at all.
     
  11. Jan 31, 2008 #10
    this is my oscillator circuit
     

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  12. Feb 1, 2008 #11

    drv

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    Your comments about inductive transfer are incisive. Coupled coils act as transformers in the near field and as radiators in the far field. Transformer designers usually do not have much experience with electromagnetic radiation methods, while antenna designers are generally not so familiar with transformer coupling. Any coil can act as a radiator, but in the near field, where the separation between coils is a fraction of the wavelength, the signal level falls off at a very high rate with distance (see my earlier comment).

    The 1 MHz problem that was originally proposed can be solved without violating FCC rules by simply transmitting a single pulse of energy. This would be essentially undetectable in the FCC interference tests, since the average power would measure near zero. It would also not cause undesirable intereference to other systems in most all cases, especially in comparison to motor starter relays and motor coil/commutators. Details on the FCC requirements can be obtained at the FCC web site. I believe that Part 15 is the applicable section of the specification. The current efforts on "spread spectrum" are currently concentrated on the UHF and above parts of the spectrum, while very little is being done at the lower frequencies. Frequency hoppers are another version of spread specturm communications.

    I do not know the qualifications of the person who asked the original question, but I had assumed that this forum is populated by persons who have above average technical capability. Nevertheless, my assumption might have been wrong, and your comments regarding interference are on the side of caution.

    My experience includes various areas of communications, physics, and other areas of science, and I, too am a ham. It just so happens that I have done a fair amount of work in low-power signal pulse transmission in this frequency range for departure alert systems. Experimentation has been essential in developing a feel for "real science", whereas too much theory and not enough measurements seem to me to be detrimental (or vice versa).
     
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