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While playing with my SDR (Software Defined Radio) Board, I was interested in performing a TX output power table at different center frequencies and TX antenna gains.

I have an RF frequency generator. Therefore, my intentions are to generate signals with well known RF power and measure them with the RX of the SDR, somehow converting it into a calibrated measuring receiver. From this, I would just repeat the experiment but now with a direct TX-RX connection. This way, I would know what power I'm transmitting with TX as well.

The problem is that I'm not really sure what should be the quantities that I measure in RX in order to make it into a measuring receiver and I don't know what the digital words measured in RX correspond to voltage neither. Also, I have to assume that RX does not have a 50 ohm impedance neither does TX. Therefore, I can't just convert the power from the 50 ohm frequency generator into Vpk and then use this result to calculate the digital Vpk of the IQ data in RX, since there would be a reflection in the wave and the result would be wrong... right? Or is there a way to measure the impedance of the RX (and then of the TX)?

Can someone please clarify me the methods? I'm not familiar with RF at all.

Thanks in advance!

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  • $\begingroup$ This is a very hard thing to do with regular SDRs; there are too many variables both in the transmitter and the receiver. Search for questions on this site mentioning "RSSI" for more information. $\endgroup$ – MBaz Jan 29 '19 at 15:11
  • $\begingroup$ Your proposed scheme can work: generate sinusoids with a calibrated signal generator at various frequencies, measure the received power at the SDR's ADC, and generate a calibration table that maps the observed power to a "real" power level like dBm. The devil is in the details: how precise do you require the measurement to be? Will your system always be at about the same temperature? How much time do you have to make the measurements (i.e. how fine of a grid will you calibrate the system on)? These are a few of the first questions that come to mind. $\endgroup$ – Jason R Jan 29 '19 at 17:29

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