RX - RX preamp BOX

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This is very simply preamplifier BOX with 2N5109 transistor based on W7IUV design. You can use it as high IP preamplifier for RX antennas (beverage, DHDL, flag etc). Gain is up to 18dB and there is also build in variable ATT. You can easy set the gain as high as you need! As well you can set right transistor bias with multi turn potentiometer. Two relays offer bypass switching if there is no power supply voltage. You can use external power supply connected to the box or the bias tee box for power over the coax.


  • High IP RX preamplifier - RX antennas
  • Buffer amplifier
  • Driver amplifier




  • Variable Attenuator and RF protections:
    • from 0 to about 18 dB
    • turn the ATT-TRIM (201)

  • Transistor Bias current:
    • disconnect jumper JP1
    • connect mA meter there (200 mA scale is fine)
    • connect supply voltage you want - from 12 to 15 V
    • turn the resistor trimmer R4 (BIAS) and set bias current you want - it should be from 60 to 85 mA - depends on application
    • than connect jumper short back again

  • Power over coax :
    • Short jumper to enable power preamp over coax - with DC voltage.
    • If you use external power supply to internal DC connector, please DISCONNECT jumper JP4 - Coax PS

Bias Tee BOX

  • You can use Bias Tee BOX for power over coax: Web page