LA6NCA, RF PROBE, HOMEBREW

This is the frequency response curve for the MF filter in a E10K receiver.
Look at the great dynamic range. 100 dB from top to bottom of the curve !!
This curve is measured with my new HF-probe and a HP network analyzer.

"A" is the input signal from the network analyzer.
This signal is terminated in a 50 ohm resistor.
The signal is then connected to the RF-mixers anode though a small capacitor and a 47K resistor.

“B” is the input signal from the MF filter output. I use here a 0.1 pF serial capacitor.
This will not interfere with the MF signal.

My new HF-probe is designed with a new type OPAMP. AD8130.
This is an opamp with separate feedback terminals. The input signals are balanced and have very high input impedance.
The + input capacitor can be 0.1 to 1 pF. This will not interfere with the radio signal in the circuit.
The – input signal shall be connected to GND near the measuring point.
The output signal is serial terminated with a 50 ohm resistor. This because we want flat frequency response from 1 MHz to 200 MHz.
The two 1K resistors give the amplifier a gain of two to compensate the loss in the serial terminated resistor.