What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?
Why An unterminated rhombic or long wire is a resonant, standing-wave antenna: current flows toward the far end, reflects, and comes back, producing lobes off both ends. Adding a resistor at the far end (typically several hundred ohms to ground or between the legs) absorbs that forward-traveling energy so nothing reflects back, turning it into a traveling-wave antenna with a single main lobe pointed away from the feed point. The cost is efficiency, since roughly a third to half the power can be dissipated in the resistor, but the gain in front-to-back ratio and bandwidth is usually worth it.
Watch out The choice about reflecting standing waves back to the transmitter is backwards: the whole point of the termination is to eliminate reflections, not create them. Polarization is set by wire orientation, and a termination resistor adds loss rather than reducing ground loss.
Terminate = travel one way. Resistor soaks up the reflection, so the pattern fires one direction only.