Do I need to install RF terminator at the end of RF attenuator? Let's say that max power output for RM port is 50W and I'm using 100W 50dB attenuator. What if I was using 50W 40dB attenuator? Is there a possibility that without proper RF load some power may reflect from the end of attenuator?

  • \$\begingroup\$ I think attenuators expect to see both their characteristic impedance (50 ohms in this case) and the input and output. This is most likely supplied by whatever you have attached to the output. But if not then you need to supply it to get the specified attenuation. \$\endgroup\$ – George Herold Sep 16 '14 at 13:43
  • \$\begingroup\$ Well, a 20 dB PI attenuator consists of two series 40.9 ohm resistors with a 10.1 ohm resistor to GND in the middle. If you leave one end disconnected, you get 40.9 in series with 10.1 which is 51 ohms, not counting the stub. So it's going to be pretty close to a terminator. It would not be a bad idea to check this out on a network analyzer, though. \$\endgroup\$ – alex.forencich Sep 16 '14 at 23:03

If your attenuator is beefy enough, you should be fine without a terminator. If a signal does bounce off and come back, it will be attenuated by 2x the value of the attenuator since it passes through the attenuator twice. Say, if you have a 50 dB attenuator, a signal that passes through the attenuator and reflects back should be attenuated by 100 dB. So some will reflect, it's just a question of whether it is small enough to cause a problem or not. 100 dB return loss is pretty darn good even for a terminator. The return loss of a loose connector is probably worse than that.


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