Total posts : 45366
[quote=radio8z]… It appears to me that if, by means of step up transformers and clever transmitter design, we can deliver 144 volts to an antenna, we do not need a loading coil. The big question is can the transmitter produce this voltage when presented with a highly reactive load.[/quote]The real power in the antenna system is a function of the voltage and current magnitudes there and to their relative phase, and is maximum when current and voltage are in phase at the antenna feedpoint, and zero when they are 180 degrees out of phase. These two conditions correspond to a VSWR magnitude of 1.0 and infinity, respectively.
A highly reactive load means that current and voltage are not in phase, so the power delivered to the load is reduced. This is analogous to circuits on the a-c power grid, where reactances are used to maintain voltage and current in phase, so as to maximize deliverable power.
In the case of the 30 -j2500 ohm example above in this thread, a tx able to deliver 100% of its rated power into a 30 ohm non-reactive load would “see” a load VSWR of 6,946:1, which would accept/dissipate only 0.03% of the tx power. The remaining 99.97% is reflected back toward the tx, and most of that is dissipated by system losses.
It doesn’t matter from a power transfer and radiation viewpoint how much r-f voltage exists at an antenna feedpoint if no, or very little current is able to flow there. Without current, the antenna will not radiate the EM energy needed for its purpose.
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