kc1dyk
Anyone know a good guide on the difference between T and pi matching networks? I've read things that say when to use each, but they don't say why, and I'm curious. #electronics #matching #swr #antennas
Nov 13, 2022 at 5:25pmWeb
Show threadSmittyHalibutNov 16, 2022

@kc1dyk For in-band signals, it doesn’t much matter. They’ll see 50(ish) ohms no matter which you use.

But for out-of-band signals, the ones you’re trying to filter out: Pi starts out with shunt components to ground, so the out-of-band energy will see 0 ohms to ground. T starts with series components, so out-of-band energy will see infinite ohms, an open circuit.

When this matters is context dependent, but that’s the primary difference.

Show threadDiane Bruce VA3DBNov 16, 2022
@smitty @kc1dyk bit of interesting history. Early transmitters were all link coupled. There was an LC tuned circuit on the output on the PA with a few turns of a coil (the link) to the antenna. When TV became popular it was noted these designs were not very good at filtering harmonics. The pi network because of it's low pass nature became popular. So tube transmitters had a built in tuner (in a way) which was one of the early complaints about solid state rigs that didn't need a pi network. ;)