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Context: I have a transponder that is explicitly stated to output 250W peaks and has been frying some nearby components. The transponder average output is not stated but the average input is 7W and 12W max. I need to do some tests with an expensive spectrometer that has a max input of 20dBm (-10dB) so I can figure out safe ranges and shielding solutions. I've got a proper antenna and have been looking at attenuators to add to the circuit to attenuate about 40dB. Most market attenuators are around '2W' which is where I'm confused.

Questions: Is the 2W label on attenuators max or average power input? How can I find max power input? If I use an 8W attenuator, would this suffice assuming almost all input power of my transponder goes to signal (standby mode is <1W)? How would I search for companies that provide these types of attenuators?

My next course of action is to take readings at a far distance from the transponder but it would be helpful to have some close up readings at around 1m. Any help is greatly appreciated.

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  • \$\begingroup\$ Can you cascade some Directional Couplers? \$\endgroup\$ Jan 7 at 23:53
  • \$\begingroup\$ They make some 50dB 10kWp, 250W attenuators for 4GHz at Lambda. You can use a 50 dB pad or a DC-40 with a 2W pad \$\endgroup\$ Jan 7 at 23:56
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I would expect the power rating of an attenuator to be the average power since it is based on the heat dissipation capability of the device. However, in your case, the peak power, 250 watts, is more than 30 times the average power (7 watts). Therefore, it is important to know the duration of the peak power pulse versus the thermal time constant of the attenuator. For example, if the peak power pulse lasts for 5 seconds, and the thermal time constant of the attenuator is only 1 second, then the attenuator will heat up substantially during the pulse and will probably melt, regardless of the duty cycle of the pulse. You should definitely carefully check the data sheet of the attenuator and/or contact the manufacturer to see if your application is suitable for the device. Just Google RF attenuators to get suitable manufacturers.

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  • \$\begingroup\$ Yes pad down with 20 dB~30 dB margin at least to protect that expensive front end in the SA \$\endgroup\$ Jan 8 at 0:14
  • \$\begingroup\$ I would be a bit surprised if the peak duration was more than ms, I imagine the FCC wouldn't be happy with something like that (depending on the frequency). What is the function and band of the transponder? \$\endgroup\$
    – BeB00
    Jan 8 at 0:19
  • \$\begingroup\$ The transponder is running at around 1GHz so I assume the peak time would be quite low. More of a blip, think squawk for aircontrol. Most thermal time constants would be able to handle that probably? Excellent advice though thank you all. \$\endgroup\$ Jan 8 at 0:47

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