I have designed an RF power amplifier that operates close to 100 MHz and amplifies signals from 50mW to about 2W. Everytime I switch it on, the voltage on my lab power supply drops even though the current is within limits. It also makes a weird buzzing noise. I realised that the RF signal is finding its way into the power supply(2V peak-peak) inspite of the 1uH choke coil L2 and the decoupling capacitors C7 and C8. Is that why the power amplifier is behaving weirdly. If so how do I solve the problem? Also the problem only occurs if I connect the antenna. I am not sure why that is so too. Could it be because of some kind of impedance mismatch or EMI?

My RF power amplifier

  • \$\begingroup\$ Not asn answer, but there might be an output impedance spec of the power source. I am pretty sure that 100 MHz out of bounds for many benchtop sources. There are radio transmitter power sources, that I hear bout in amateur radio communities. (i.e. Reddit) Sometimes ARRL Handbook proves itself very useful in such cases, I am sure that it has a section discussing power sources. \$\endgroup\$ – mehmet.ali.anil May 31 '18 at 9:27
  • \$\begingroup\$ That doesn't explain why it happens only when I connect the antenna. I mean if I don't connect the antenna but I start sending an input signal, the current draw rises but the voltage doesn't drop. But once I connect the antenna, voltage drops to about 10V even though the current draw doesn't increase. \$\endgroup\$ – Kevin Selva Prasanna May 31 '18 at 9:31
  • \$\begingroup\$ Question: Is this in simulation, or in real? \$\endgroup\$ – mehmet.ali.anil May 31 '18 at 9:32
  • \$\begingroup\$ No, this is real life. Everything is beautiful in simulations. \$\endgroup\$ – Kevin Selva Prasanna May 31 '18 at 9:32
  • \$\begingroup\$ Can it be because until you connect the antenna, you do not feed the antenna power, due to the impedance mismatch? When you connect it, you actually transfer power, and start extracting that power from the source. Maybe it will help to use a cable to distance the transmitter to the antenna, but if I had to guess, I would say it is due to droop due to drawing high current, high frequency. \$\endgroup\$ – mehmet.ali.anil May 31 '18 at 9:34

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