Biastee,
1. The values of inductances are L1=L2=La/2 and C=Ca based on S11 measurements for a particular loop antenna. So, the dummy circuit is a simple Pi- attenuator balanced with 50 ohm resistor in shunt arm towards the generator port and 0.5 or 2 ohm resistor in shunt arm towards the amplifier under test. In addition, between the attenuator and input ports of amplifier under test to include as well as a dummy antenna circuit consisting of series arms L1=L2=La/2 and shunt arm towards amplifier C=Ca.
2. I am not sure if the LPF in LZ1AQ's design serves as an equalizer for the frequency response of the amplifier from 15 to 25 MHz.
I crossed another paperwork, where was presented S21 of this LPF. At frequency 20.05 MHz -5dB drop, at 40.05 MHz a further drop -35 dB, at 60 MHz -60 dB and
at 80.05 MHz -70 dB.
Also, the frequency response of amplifier itself with added just two capacitors 100 pF but without the LPF filter: S21 - for BW=125 KHz - 27 MHz +/- 3 dB
I agree the inductances 300 nH will increase the input impedance of the amplifier but it might with parasitic input capacitance of amplifier to roll off at 20.5 MHz the frequency response of amplifier.
Regards,
Raphael
