High pass filter in PI4

[6666]

Hello Carl can I ask which components make up the hi pass filter in the PI4 ?, thanks.

[Qiaozhi]

Hello Carl can I ask which components make up the hi pass filter in the PI4 ?, thanks.

The high-pass filter is formed by C2 (1uF) and R4 (10k).
C2 also acts as a dc blocking capacitor since the TX circuit runs from directly from the battery, but the preamp input needs to be referenced to the virtual ground created by IC1b.

[6666]

The high-pass filter is formed by C2 (1uF) and R4 (10k).
C2 also acts as a dc blocking capacitor since the TX circuit runs from directly from the battery, but the preamp input needs to be referenced to the virtual ground created by IC1b.

Thanks reply, I have been investigating the PI4 and how it rejects EFE, I can wave a magnet all over any coil and not a sign of EFE, the interesting thing is I can remove R4 10K and the circuit works perfectly normal, still no EFE, I use two 5 volt battery's.