CRAC Class A (2025) — Questions 471–480

Per the question's marked answer, the Type M connector is widely used in HF and VHF communication systems (A). The other descriptions — threaded/waterproof (B), bayonet quick- connect (C), and expensive microwave use (D) — are distractors for this item.

A vertical antenna radiates vertical polarization (E-field vertical, A correct) and is omnidirectional in azimuth — which is the H-plane — so the H-plane pattern is circular/omnidirectional (B correct). For vertical polarization the magnetic field is horizontal, not vertical (C wrong); the E- plane (vertical cut) is not omnidirectional (D wrong).

A horizontal dipole radiates horizontal polarization (E-field parallel to ground, A correct). The plane containing the element is the E-plane; for a horizontal dipole that plane is horizontal, and its pattern is the figure-8 (B correct). C is wrong (that is vertical polarization); D swaps the E/H planes (the H- plane of a horizontal dipole is the vertical cut, which is omnidirectional).

Initially both horizontal dipoles → matching polarization → good. Changing one to vertical creates cross-polarization (horizontal vs vertical), which loses roughly 20+ dB, so communication deteriorates (A).

Initially cross-polarized (one H, one V) → poor. After both become vertical → matching polarization → improves (A).

Initially cross-polarized → poor. After both become horizontal → matching polarization → improves (A).

Initially opposite circular polarizations (LHCP vs RHCP) → near- complete rejection, very poor. After both become LHCP → matched → improves (A).

Same as U0476: initially mismatched opposite circular polarizations → poor; both RHCP → matched → improves (A).

A linear polarization (horizontal or vertical) can be decomposed into equal left- and right-hand circular components. Thus a circularly polarized antenna receiving a linear signal (or vice versa) always captures half the power (−3 dB) regardless of the linear orientation. Changing station B from a horizontal to a vertical linear dipole still yields the same −3 dB, so the effect is unchanged (A).

A linear polarization (the dipole) contains equal LHCP and RHCP parts, so a circularly polarized antenna — whether LHCP or RHCP — captures the same half-power regardless of its sense. Switching A from LHCP to RHCP while its partner is a linear dipole yields an unchanged result (A).