Signal strength in uV, dBm, dBuV, uV/m, dBuV/m or what?
Borrow a calibrated signal generator (with calibrated output power level):
1) Record the signal strength from the repeater on the S-meter of your trcvr.
2) Replace the antenna connection to the trcvr with a short coaxial cable from the signal generator. Increase the signal level from the generator until the same reading as in 1) above is obtained on the S-meter on your trcvr.
3) Now read the power level in dBm or uV on the display on the signal generator. This is the signal strength (in dBm or uV). Accuracy is depending on the VSWR of your trcvr RX input, fading, etc.
4) I you would like to measure signal strength in uV/m or dBuV/m (field strength), the procedure 1) to 3) above is the same. But to convert signal strength reading in dBm or uV to field strength, an additional step is required. This requires knowledge of your receiving antenna gain, receiving radiation pattern and cable loss.