Introduction
The recent article Mullard QY4-400 (4-400) x 2 Class C AM plate and screen walked through design of a valve PA for a given power supply, power out etc, arriving at the required resonant load impedance.
This article walks through the design of transmitter pi coupler output, and antenna system (feed line + antenna).
Above is the result from Calculate initial load line of valve RF amplifier.
It is popular today to design the transmitter for a nominal 50+j0Ω load, then use an ‘ATU’ to transform the antenna system load to the transmitter, but in earlier days before VSWR meters were so popular, the pi coupler would simply be adjusted to achieve the desired operating point and power output. This article follows the latter path. Continue reading System perspective from valve plate to antenna feed point