On Sun, Mar 19, 2023 at 01:24 AM, Tom Seeger wrote:
Could you help me understand what I'm missing??
Hi Tom,
The amplifier itself plays an important role and we are basically trying to make its input impedance track that of the loop.
The input filter forms a resonant peak in the amplifier response at a frequency that is close to the resonant frequency of the loop.
A typical sized broadband loop will have a resonance at just above 30MHz. If we connect another tuned circuit with a similar resonant frequency in parallel, the two will interact as although the capacitance may be doubled, the inductance will be halved, so the resonant frequency remains about the same.
By altering the values of the capacitors in the low pass filter network, you can shift the combined resonant peak over a reasonable frequency range, but if the loop inductance is too high, its self resonant frequency will be too low to be able to shift it high enough in frequency for this trick to work.
It sounds counter-intuitive, but try it and see.
Regards,
Martin
