1
\$\begingroup\$

I'm looking at Wi-Fi 2.4 GHz power amplifiers and I can't find a single high power (500 mW) one including a system protecting it from damage. I can, for example, find some ~ GHz PA with protection circuits, for example from Triquint (7m9106).

I burned some PAs in some of my designs over the years but in my real world experience with electronics, I don't believe I ever damaged a device by powering it on without an antenna installed.

  • How are "high power" (500 mW) consumer electronics protected against users powering it on without antenna installed?
    • Has the power detect output pin common in most PA anything to do with it or is it just for feedback on how the PA is performing?
  • How do I understand from a datasheet just how likely a PA is to self destruct when operating without antenna?
\$\endgroup\$
  • 1
    \$\begingroup\$ Do you have a circuit example of one? Do you have access to design files for it? Is there written material that says you shouldn't do this or can do that? Impossible to answer otherwise. If, on the other hand you asked a different question that asked how you might be able to protect a design from antenna removal and gave some indication of the length of antenna coax, you might just get an answer. But for this no and I'm voting to close as unclear. \$\endgroup\$ – Andy aka Jun 2 '18 at 21:11
  • \$\begingroup\$ You can look at any datasheet for a circuit example. What design files? My personal experience is PAs blowing up without antennas, all of them aside from that triquint, who is quoting advanced protection features in its datasheet. My experience before that was mostly limited to 900 MHz PAs. If your experience differs please simply say so. I also see absolutely zero relationship between the length of an antenna coax and PAs blowing up when not connected to an antenna. \$\endgroup\$ – Mara Ara Jun 2 '18 at 23:07
0
\$\begingroup\$

The best way to protect against a disconnected or malfunctioning antenna system is an SWR feedback circuit where the power is reduced when a high SWR is detected. Some amplifiers will have a maximum SWR listed in the data sheet which will give you some idea of how likely they are to be destroyed with a high SWR.

SWR or Standing Wave Ratio (indirectly) measures the amount of power reflected back towards the transmitter relative to the amount of power produced in the transmitter (it really measures the ratio between the max ac voltage along the transmission line and the minimum ac voltage). Power being reflected towards the transmitter can be damaging because it can cause the output transistors to exceed their voltage or current ratings. Power is reflected any time there is an impedance mismatch between the transmitter (usually 50 ohms), the feedline (50 ohms) and the antenna (ideally 50 ohms, can be anywhere between 1-2 ohms to several kilohms depending on the antenna, or 0 and infinite ohms if the feedline is shorted or no antenna is connected).

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.