Sorry for this OT post, but this is the group I lurk around in and I'm sure someone here has come across this application note for the ATA8402 (T5754) Atmel 433MHz transmitter:
I have very little RF experience and I might be mistaken, but this AN is very dodgy indeed. I'm trying to make sense of the impedance-matching capacitor calculation.
The main problem is that the equations are not accompanied by numeric examples for the demo board handled in the same AN. Apart from this, the equations given don't take into account the RF choke, nor the added Lx,Cx filter in the demo board.
But OK, I don't even understand the matching-capacitor equations as they are presented. If I understood correctly, we get Z|| from Eq. 8, then use Eq. 9 to calculate r, which we later use to get the matching capacitors. To get r, we need to use the ideal Zload, but this is given as
166+j223 Ohm, i.e. a complex number, while Z|| and r are obviously real numbers. So, I'm stuck at Eq. 9 and have no idea how to proceed. I have asked Atmel support what Zload is and received a short and (for me) useless response stating that Zload is complex, but giving no hint as to how the quotient of a real and a complex number should result in r, a real number. I asked again and have received no response.I have since read application notes for competitors' TX chips, some of which are well written and comprehensible even for an RF beginner like me, but their IC's do have real output impedances so this problem doesn't arise.
Thanks for any suggestions.
Viktor