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The analysis and the measurement technique of the RF transformer model is presented. Transformer is used to improve the SNR of the input stages and for DC biasing through the winding inductance. The frequency range 0.1 MHz to 10 MHz utilized by the conventional ultrasound is assumed. Model is incorporating the winding resistances and the core loss resistance. The winding resistances experimental measurements and the modelling results comparison are presented. It has been indicated that winding resistances variance of plusmn20 % is causing only 0.02 dB variation in the preamplifier noise figure if source impedance is low. The core loss resistance measurement and experimental investigation results are outlined. It is shown that plusmn20% variance of this resistance can cause preamplifier noise figure variations reaching 0.03 dB for high output impedance transducer.