# RF transformers in first, second and third IF stages, how and why are they different?

Many websites about RF transformers talk about IF transformers to be implemented in first (green slug), second and third (brown, black or orange slug) 10.7 MHz IF stages. Other than this, I don't see any elaboration on why transformers with different impedance ratios would be used for the cascaded stages. So what is the difference and why is it important?

• Datasheets for the IFTs will show you the differences. It's important because they are driven from different things and drive different things. Only the first IFT is driven from a mixer for example. Only the last drives a demodulator or second mixer. – Brian Drummond Sep 21 '20 at 10:20
• Also consider that the IF chain is likely not all the same impedance. The fact that transformers have an inverse characteristic ($V_P\cdot I_P \approx V_S\cdot I_S$) of the primary and secondary means they can greatly be used to transform/match impedances. – rdtsc Sep 21 '20 at 12:35