I have a radio with a nominal output of 1-30mW (frequency dependent) and amplify this with a 21.8dB capable amplifier (frequency dependent, but should be ~150mW). The signal output then passes through a -20dB attenuator to my frequency counter. The frequency counter reads 121mV/-5.3dBm.
How can I calculate my amplified signal output, before -20dB attenuation? I understand -20dB is a reduction by a factor of 100. How do I calculate dBm/mW output?
Can someone provide clarity?
Note: This frequency counter reads 2.2dBm/287mV when I transmit with a UV5R (~2W) 5cm from it. I guess this could be a problem, since it sees only 1.7mW. This UV5R transmits >25km easily. The frequency counter is a Surecom SF-103.
Update: The Surecom SF-103 frequency counter cannot react quickly enough to changes in frequency (within a range of ~5KHz), and so it displays nothing. The solution was to output a stable signal, then it works fine. Signal strength is still not displayed correctly, even with the right shielded cable for UHF.