Loosing RX while Transmitting

  • Hello All,

    i am looking for an help that i cannot find the solution.

    I have made two cases, In one ( Picture on the right side ) i have just two PSU

    one 36v set to 28V to power the SG-Labs 20W Power Amplifier for 2.4GHz and the Big PA by F4VSG.

    In the Other case ( Picture on the left ) i have the two PA, one RX filter, the CN0417, one 12V to 5V converter to power the CN0417

    and a Bias Tee.

    My Problem: is While i am RXing the QO-100 signal, as soon i go in TX also without giving power, the RX signal drops

    down until i do not pass again in RX.

    If i try to use an external 12V power supply powering with it just the Bias Tee, the problem does not pop up.

    I am struggling from several weeks without getting the solution.

    Please anybody can help me to eliminate the problem?

    Any help will be really appreciated.

    If you need more info, please do not hesitate to ask me.

    Thanks in advance for any help or suggestion.

    73's de Enzo IK8OZV

  • Renauld,

    Thanks for your description of the problem but what i cannot understand is why the issues does not pop up also

    when i use an external PSU?

    Please can you tell me with which one you have substitute it maybe also with a photo of it?

    Thanks a lot


  • Hi Enzo.

    You probably have some RF feedback on the power supply line at its T Bias. When you use external power supply you isolate this way. In the Bias T +12 VDC try:

    - Use some ferrite (bead, core or choke).

    - Use some capacitors for RF decoupling (or feedthrough capacitor).

    - A shielded cable for power supply.

    73 de PY1SAN


  • I was told many times not to have microwave PA's in the same box as anything else, and to have the big PA in a totally separate, screened enclosure with even the door well grounded to the main body with a wide copper braid strap. A friend ignored this and put his Pluto and cabling and pre amp in with the PA, and had terrible problems. Then he moved the PA into a separate steel box, and all worked fine... Good luck!

  • Renauld please can you post a picture of the Bias Tee you using that do not cause anymore the problem?