RF circuit testing

Discussion in 'Wireless & RF Design' started by Htrahdis, Dec 2, 2015.

  1. Htrahdis

    Thread Starter New Member

    Nov 26, 2015
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    0
    How do I test the functionality of an RF circuit, say an oscillator that has been designed and the circuit diagram is available. Now I want to check the open loop gain of the circuit and the corresponding frequency response, with different values of components, if it is less than 1, replace a component and test it again. For these , when I used a breadboard, it proved to be very troublesome, and gave erroneous answers. The resonant frequency peak would rise no more than a MHz, when the intended frequency was 27 MHz. I have <100pF capacitances and sub uH inductors in my circuit.
    So is there any way out to do this task before I come up with a good working circuit and do the pcb design?
    Would dot boards (perf) be a good idea ? But the components go waste everytime they are soldered.

    Any inputs please ?
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    428
    rf circuits, especially higher frequency circuits are very susceptable to lead length and part placement. you mention sub uH inductors, the leads may be more inductance than the inductor, and capacitors may have unwanted inductance in their leads too. there are several good references on design and building practices for rf circuits available.
     
  3. Htrahdis

    Thread Starter New Member

    Nov 26, 2015
    3
    0
    thanks for your input, alfacliff, but where can I find those materials you mentioned ?
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
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    one good sourse is "the radio amaturs handbook" published by the ARRL. chapters on construction, vhf and uhf design, componants, and more.
     
  5. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    If you are using an oscilloscope for R.F., be SURE you are using a high impedance probe. Even a probe with 10pf of capacitance can seriously detune a tank circuit if you connect it directly. Most of the time, you can "sniff" an R.F. circuit by just placing the probe tip near the tank circuit in question...if absolute voltage measurement isn't required.
     
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