Receiver gain measurement

[ctzof]

Hello,

We want to calculate the real gain of a transceiver board in reception for various bandwidths at 2.44 Ghz. We use a simple AM modulation scheme with a sinusoid as information signal. So we fix the transmitting power at a desired level and then we measure for each signal frequency and for each gain value of the DGA (Digital Gain Amplifier) the baseband I and Q signals at the receiver with an oscilloscope. The I and Q signals are sinusoids and we measure pk-pk amplitude and power in dBm through oscilloscope's FFT function. How can we use these I and Q signals to measure the power in the receiver, with a program like Matlab?

 

[jiripolivka]

RF power is measured by a power meter. Receiver gain can only be measured in linear terms, so no demodulator is involved.
I and Q outputs from receiver demodulator are affected by demodulator non-linearity, so no power response can be evaluated that way.

To evaluate I/Q outputs from a receiver you must transmit corresponding I/Q signals through the test transmitter and attenuator.

RF power levels-again- can be measured by RF power meter, and you need to use I/Q demodulator specifications to derive output amplitudes from the input RF power.

 

[biff44]

well, ASSUMING the receiver does not have an "automatic gain control" (AGC), you would input a test signal (maybe at -90 dBm level) directly with a cable to the receiver front end. You would measure the magnitude of I and Q, and figure out the IF output power. Vifout=√((I^2)+(Q^2))

Then gain is simply Pin/Pifout