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Designing a signal generator

  1. Oct 12, 2014 #1
    I am very new to circuit design so any help is much appreciated. I need to design a signal generator that will output about 30V-40V peak to peak at 13MHz (sine wave) If the signal generator is not able to, then I need some kind of amplifier. So far I have looked into Hartley and Colpitts oscilators and am not having any luck reaching my desired output. Any help or suggestions would really help. Thanks in advance
     
  2. jcsd
  3. Oct 12, 2014 #2
    Is 13 MHz the only frequency the signal generator needs to produce?
    What will the load be on the signal generator (how much current)?
    Is the load strictly resistive or can it be capacitive or inductive?
    Will the load be constant or variable and if variable by how much?
     
  4. Oct 12, 2014 #3
    I would like to keep the frequency around 13MHz but if the output can be reached at lower/higher frequencies then the output takes priority. The load can be resistive, capacitive or inductive. The load is constant and I am not too sure about the current, but like to keep the current at a minimum though
     
  5. Oct 12, 2014 #4
    Knowing how much current or better yet the impedance of the load is very important. If your load is connected by coax and the coax is more than about a meter and the load doesn't have the same impedance of the coax or the coax isn't the same as your signal generator, your output will be reduced. A VSWR meter can tell you if you are matched or not. If you aren't you can make of buy a matching network which you can adjust until you get a minimum reading on the VSWR meter.

    Without seeing your circuit or knowing what your load is, I can't help you any more.

    Will your signal be radiated? There are broadcast stations in the 12MHz frequencies, marine mobile around 13 MHz and radio astronomy above 13 MHz. A mismatch between generator and load as well as an improper ground can cause it to radiate. Recently two ham operators near Cleveland were fined $30,000 collectively for abusive radio transmissions.
     
  6. Oct 12, 2014 #5
    Someone unskilled in the art is unlikely to fabricate such a generator cheaper than one can be purchased. Common signal generators reach 20 MHz, but are limited to about 20Vp-p when terminated into 50 ohms. It would require a 16 watt amplifier to barely achieve 40Vp-p into 50 ohms resistive, 32 watts for 25 ohms, and 8 watts into 100 ohms. So, knowing the load and being able to match to it is very important (see transmatch).
    13.56 MHz is an ISM frequency reserved for equipment that might inadvertently radiate, so there is a convenient frequency nearby.

    All of this is a bit much for a hobbyist to fabricate, but readily available to purchase.
     
  7. Oct 12, 2014 #6

    Baluncore

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    Science Advisor

    A pair of mosfets, (as used in a switching power supply), would generate a square wave, that could then have a resonant tank circuit to remove the harmonics.
    The OP specifies a sine wave. What level of harmonic content is acceptable?
     
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