1db compression

If you look at the data below I put an input signal in and record the output and then calculate the change. So I basically expect to see a change in 1 dB if I change the input by 1 dB.

At which point would the 1dB compression point be? At -19 dBm? I'm not sure what the margin is in determining 1dB compression. Could it be at -25 dB?

Input (dBm) Output (dBm) Change (dB)
-30 -16.45 0
-29 -15.43 1.02
-28 -14.42 1.01
-27 -13.51 0.91
-26 -12.60 0.91
-25 -11.77 0.83
-24 -10.96 0.81
-23 -10.42 0.54
-22 -10.15 0.27
-21 -9.900 0.25
-20 -9.780 0.12
-19


Thanks for the help.

1dB compression is a Gain compression.

So you need to calculate gain G0 (Pout-Pin) in linear condition (in your case -30 is ok), increase Pin and find the Pin that gives you G0-1 (probably between -20 and -19).

Mazz

I think it's closer to -22 or -23. your 3rd collum is just

Pout(x) - Pout(x-1)

So this number looses its linear approximation. I use to measure -1dB Comp
with a 10dB Step attenuator. Is what you do is put the Step Attn. in front of
the input signal. Now set the Pin to (as Mazz said -20dBm) and read your
Output Pwr to see what is your Gain:

@ Pin = -20dBm ---> Gain = Pout - Pin= -9.780 - (-20) = 10.22dB

Now step up the Atten. by 10dB. The new Pin will be 10dB lower (-30dBm).

@ Pin =-30 --> Gain = Pout - Pin = -16.45 - (-30) = 13.55

If Pin = -20 was the -1dB CP then the Gain at -30 dBm ( -20 +10dB Atten)
should be 10.22 + 1dB = 11.22 ( 1dB higher than -1dBCP), But since the Gain at
Pin =-30 is measured to be 13.55, then we need to find were (Pout - Pin) =12.55

Assuming that 13.55dB is the nominal gain, it looks like the 1db Comp point
is between -23 & -24 .

Cheers

agree.
between -23 and -24.

Mazz