In a 2N3904 common emitter RF amplifier circuit that I am building, the designer uses a FT37-43 miniature core with an 8 turns primary : 2 turns secondary ratio to couple to the next stage. I understand the purpose, it is impedance matching between the two stages.

My question is, what would the consequences be for using a 16:4 turns ratio instead of 8:2? The ratio is the same so the impedance match should be the same but I am thinking don't do it for these reasons: the larger number of turns will reduce the power capacity as you will saturate the core at a lower signal level, the inductance seen at the collector of the 2N3904 would be four times as great, the Q factor drops because of the 2x resistance of the added wire, and physically fitting that many turns may not be possible.

Any other reasons?

  • \$\begingroup\$ Is your amplifier a resonant one ? \$\endgroup\$
    – fraxinus
    Jun 16 '21 at 19:46
  • 1
    \$\begingroup\$ 8 turns on a core \$ 0.42uh/t^2 \$ yields 27uh...that may resonate with local capacitance near the design frequency. Or that local capacitance may reduce bandwidth of a broadband amplifier if you wind it with more turns or cause a gain peak in an otherwise-flat broadband amplifier. \$\endgroup\$
    – glen_geek
    Jun 16 '21 at 19:47
  • \$\begingroup\$ No, the amplifier is not a resonant amplifier. It is an approximate 9dB pre-amp for a signal around 10MHz. \$\endgroup\$ Jun 17 '21 at 1:48

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