[3rd Order Intercept Point]

Hello,
        Say if I have two amplifiers connected in cascade with the following specifications:

Apmlifier 1:  Gain      Noise Figure      OIP3
                  15 dB          3 dB            15 dbm


Apmlifier 2:  Gain      Noise Figure      OIP3
                  15 dB          5 dB            20 dbm


Note:  OIP3 = third order intercept point.

I calculated the overall gain, the overall noise figure and the overall third order intercept point.

Overall gain = 30 dB

Overall noise figure = 3.146 dB

Overall OIP3 = 19.586 dBm  (= -10.414 dB)

My question is:  What does this level of OIP3 mean?  I know how to calculate it etc., but not what it actually means.  For example, what happens if my RF input was greater than 19.586 dBm??

Any details you can impart will be much appreciated.

RF Burns

[dBm to Vrms]

Dear all,
              I generated a 50 MHz, -10 dBm sine-wave using a Rhode & Schwarts RF signal generator.  I checked this using an Agilent spectrum analyser and, as you'd expect, I get my tone at 50 MHz with peak amplitude of -10 dBm.  However, when I input my RF signal to a TDS 210 Tecktronix Digital Oscilloscope, the peak-to-peak voltage is 336 mV and the Cyc RMS voltage is 117 mV.  Now, on the TDS210, Cyc RMS calculates the RMS voltage over one complete cycle of the waveform. 

When I tried to calculate this I got a different answer:

P = -10 dBm, which is equivalent to 100 uW
Now, P = V^2 / R 
I've taken R = 50 ohms
Therefore Vrms = sqrt(P x R)

That is: Vrms = sqrt(100 uW x 50 ohms)

So, Vrms = 70.7 mV 

This is different to the 117 mV measured on the oscilloscope??