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authorVadim Yanitskiy <vyanitskiy@sysmocom.de>2021-01-26 23:55:22 +0100
committerVadim Yanitskiy <vyanitskiy@sysmocom.de>2021-01-27 01:01:50 +0100
commit2a637a5c9c1b6e77c00701004ba504ba9d020b28 (patch)
tree54d5ed98c0303e384d81fe52ffc9d1bcb0de3bce /configure.ac
parent819cad1776e09782fffdf433a2e843fe5720d6c8 (diff)
Transceiver: use proper factor for amplitude scaling
In Transceiver::addRadioVector() we scale the I/Q samples by scaling the output voltage of the DAC. A relative factor/divisor/ration in the voltage domain cannot be used 1:1 in the power domain. There exist two similar formulas: a) X_dB = 10 * log10(X_lin / X_ref) b) Y_db = 20 * log10(Y_lin / Y_ref) both of them are correct, and according to [1]: a) If you convert a quantity X that relates to power or energy, => the factor is 10. b) If you convert a quantity Y that relates to amplitude, => the factor is 20. Therefore we should be using 20 instead of 10. This change makes osmo-trx apply per-lchan attenuation values correctly. Otherwise it would double the values indicated in TRXD messages. [1] https://dspillustrations.com/pages/posts/misc/decibel-conversion-factor-10-or-factor-20.html Change-Id: I98bc00bd25df4913d45e55eb008d715aca76fc7c Related: SYS#4918
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