# How not to burn LimeSDR?

I got a kind of newbie question, even a few.

According to this topic maximum input power of LimeSDR is 12dBm. I did some computation according to these formulas and apparently for a 50 Ohm antenna RMS voltage should be 850 mV to get close to this level:

>>> import math
>>> rms = 850 / 1000 # 850 mV
>>> P = math.pow(rms, 2) / 50
>>> 10 * math.log10(P / 0.001) # dBm
11.598678470925666

I tried to measure RMS for one of my antennas using a 100 Mhz oscilloscope and it showed ~50 mV. I’m not sure whether one can measure an RMS for 2.4 GHz antenna this way but at least this measure gives an impression that for regular protocols (Bluetooth, Wi-Fi, GSM, …) you can’t just receive 0.85 V from the air.

So basically my question is - is it true that in most cases it’s quite hard to burn LimeSDR by being too close to a signal source (for “regular” protocols)? If not is there a better way than described above to determine whether it’s safe to turn LimeSDR on?

And a few more related questions. Is it safe to use LimeSDR without an antenna (e.g. switching an antenna on the fly)? Do I need to use a dummy load on any of unused u.FL connectors? Are there any other scenarios of burning LimeSDR (except, say, spilling a coffee on it) I should be aware of?

From a practical view of a licensed amateur operator, +12 dBm is a lot of power. A strong signal is -73 dBm, and a strong broadcast (FM station) is maybe -50 dBm. I would never look to go more than 0 dBm for fear of overloading the front end - even if it doesn’t damage the radio.

The maximum legal (USA) output for a bluetooth device is 100 mW or +20 dBm, and for a wireless LAN is 200 mW or +23 dBm. So if I were to connect the LimeSDR to such a device, I would start with two back-to-back (in series) 20 dBm attenuators, for a total of 40 dBm attenuation. An attenuator example is here: