tinySA | Main / Safe measurement of the output of transmitters

Calculating with dB is not too difficult.
Every factor of 10 increase of the power of a signal raises the dB level with +10dB
Every factor of 10 decrease of the power of a signal reduces the dB level with -10dB

Typical output power of a transmitter

100W equals +50dBm
10W equals +40dBm
1W equals +30dBm

For best measurement of harmonics in the output of transmitters the input level of the tinySA should aim between -20dBm and -10dBm

Required attenuation between transmitter and tinySA

For 100W : between 60 and 70dB
For 10W : between 50 and 60dB
For 1W : between 40 and 50dB

The best approach is to use ALWAYS a 30dB attenuator directly connected to the tinySA and to use power attenuators to reduce the output of the transmitter to the target input level of this 30dB attenuator, that is +10dBm

So you will need these power attenuators

For 100W output: 30-40dB
For 10W output: 20-30dB
For 1W output: 10-20dB

Another option is to use a dummy load and an inline 50dB attenuating sampler. A nice example of how to build one yourself can be found here