13.56 MHz 10watt Power Amplifier

Discussion in 'Wireless & RF Design' started by musclemania05, Apr 11, 2016.

  1. musclemania05

    Thread Starter New Member

    Feb 21, 2016
    Hello so attached is my power amplifier that suppose to prove 10 watts into a dummy load using a frequency of 13.56MHz. THE PROBLEM IS THAT IM ONLY GETTING 3 WATTS ON A WATT METER. Im driving 26.4dbm(little over 1/4 watt) into the base of my transistor. The transistor im using is the 2SC1969 BJT. Attached is the data sheet. I use a PI network to match 50 ohm to 5.6 ohm at the base. The PI NETWORK formula is as followed.
    Q =√(1/2−1)
    Xc1 = 1/
    Xc2 = R2 √((1/2)/(^2+1 −1/2))
    XL = R1[(+2/2)/(^2+1)].

    Then for 10watts of power a load resistance of 7.2 ohm is presented at the collector using the following formula.

    Load Resistance = Vcc²/2*Pout

    I then use a L-C-C network to match the 7.2 to the 50 ohm dummy load using the following formula.
    XL = QRs
    XC2 = RL√[Rs (Q2 + 1)/RL – 1]
    XC1 = Rs (Q2 + 1)/Q[QRL/(QRL – XC2)]
    L= XL/2πf ,C = 1/2πfXC.

    Note:( i could of just used another PI network here)

    The Q have have chosen for both networks is 3.

    I cant seem to understand why im only getting 3 watts on the watt meter unless the watt meter isn't calibrated right cause i feel all my calculations and values are correct.
  2. musclemania05

    Thread Starter New Member

    Feb 21, 2016
    Just in case the images for the equations for the L-C-C and PI newtorks arnt clear. I have attached the two. First LCC then PI
  3. bertus


    Apr 5, 2008

    You are getting the power as expected according this graph of the datasheet:


    Put more power in to get more out.

  4. musclemania05

    Thread Starter New Member

    Feb 21, 2016
    Okay that makes sense but my frequency is 13.56MHz and this one is 27MHz?
  5. Picbuster


    Dec 2, 2013
    Why are you want to use 13.56Mhz this seems to be the world standard for RFID?
    As far as I know is worldwide 100mW maximal allowed in that band but correct me when wrong.
  6. recklessrog


    May 23, 2013
    That frequency is used for RFID and high power is used to block the sensor by overloading. If anyone was caught using such a device, it would be likely they would face criminal proceedings here in the U.K.
    In view of this, I cannot give any assistance to this thread and suggest that no one else does either.
  7. JohnInTX


    Jun 26, 2012
  8. Wendy


    Mar 24, 2008
    I can speak from experience on this one. It is an industrial frequency used in many processes. We had 150W plasma ashers for the clean room, it is also used in many other applications where RF plasma is needed. These boxes do not radiate, the energy goes into ionizing the gasses and whatnot.

    As for the difference between 27Mhz and 13.5Mhz, the basics remain the same. If your watt meter is rated for that frequency and the load is correct (they can drift over time or even just burn out) then trust your meter.
  9. recklessrog


    May 23, 2013
    This evening I ran this past a friend who works for a fraud investigation agency that is used by insurance companies and large retailers.. Thieves are using devices that do radiate within the RFID bands to bypass the security systems employed in the detection of shoplifting. That being the difference to the legitimate non radiating applications.
    Until the tread starter states his intended purpose, I think it wise not to get involved in case of some possible future litigation .
  10. k7elp60

    Active Member

    Nov 4, 2008
    I understand what you are saying Wendy. I would like to talk to you more about this subject. Is there a way we can talk more about this?
  11. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    I agree with Wendy. There are a few "industrial frequencies" that are essentially unlicensed in various bands. Where I worked we had a RF sputter etch and RF sputtering (1000 W) that operated at 13.56 MHz.
  12. KL7AJ

    Senior Member

    Nov 4, 2008
    13.56 is also used for most inductively coupled plasma devices (ICPs). RFID is the interloper.