Posts by G3XOU

  • What TX amplifier do you plan to use?

    NOKIA AMP MODIFICATIONS FOR DATV AND REPAIRS TO BIAS SUPPLIES

    Hi All,


    Like some others I had intermittent problems with the Bias supplies for the PA and Driver with Iq varying wildly . The faulty parts were quickly located using Freezer spray.

    In each case the Driver IC supply decoupling capacitor was intermittently breaking down. In addition the 150ohm resistor which feeds the bias decoupling capacitor from the +28v supply on the PA Bias was intermittently varying in resistance. I've removed the SMT part and replaced it with a standard 150 ohm resistor. I carried out the "snowflake" modification on the output of the pre-driver as Roland, DM5RM modification and added a "snowflake" to the PA Driver output.


    Results :

    Vs=28v

    Iq=1.9A

    Freq: 2405MHz

    RF input: +9dBm

    RF Output: +48.2dBm (P1dB)

    Gain: 39.2dB

    Ic = 8.2A


    Reducing power to +45dBm, Ic = 6.3A


    Interesting Video of a tear-down of a NOKIA Base Station including this PA module at:


    http://kaizerpowerelectronics.…n-power-amplifier-part-4/

    Some photos follow showing Modifications and bias regulator repairs.


    73, Dave G3XOU









  • What TX amplifier do you plan to use?

    Hi Richard,


    I confirm that Andrew amplifier module from Bison Electronics is by far the easiest to get working on 2.4GHz. I've made no changes apart from adjusting the input trimmers for best return loss:


    2400MHz 25dB, 2408MHz 35dB - lowest was on 2411MHz at 43dB


    With a 28V supply and a quiescent current of 1100mA on each device checking the gain on 2.2GHz, I got 17dB, and at 2.4GHz 15dB. With 3W of RF input it gives 100W RF output on 2.4GHz, current 7.75A and that includes 150mA for the heat sink cooling fan, so it's about 50% efficient. Heat Sink temperature just reached 40 deg C and stabilised running at this level for an hour.


    Reducing the RF input by 3dB gave me 50W output on 2.4GHz, current 6A.


    I've made up temperature compensated bias regulators using the LP2951 IC with a 1N4002 used as a temperature sensor, one glued either side of the heat spreader.


    The quiescent current is very stable over a wide range of temperatures only varying a few mA from the ambient level set of 1100mA for each device.


    I've attached a photo of the Andrew Amplifier setup and also a circuit diagram of the bias regulator in case you are interested.


    73, Dave G3XOU