What is the critical frequency for reflection at vertical incidence if the maximum value of electron density is 1.24 × 10⁶ cm^-3?

Coupling into and out of a traveling-wave tube can be accompanied by a

A. Waveguide match

B. Cavity match

C. Direct coax-helix match

D. All of the above

When it is desired that short-range targets be clearly seen on a pulsed-radar set, it is important that the receiver and display system have

A. A long time constant

B. Low-pass filters

C. The shortest possible time

D. The restricted high-frequency response

The antenna separations (in meters) required for optimum operation of a space diversity system can be calculated from:
where R = effective earth radius (m) and L = path length (m)

A. $${\text{S}} = \frac{{2\lambda {\text{R}}}}{{\text{L}}}$$

B. $${\text{S}} = \frac{{3\lambda {\text{R}}}}{{\text{L}}}$$

C. $${\text{S}} = \frac{{\lambda {\text{R}}}}{{\text{L}}}$$

D. $${\text{S}} = \frac{{\text{L}}}{{\lambda {\text{R}}}}$$

The aquadag coating on the inside of PPI tube is used

A. To focus the beam of primary electrons

B. To shield the electron beam from unidirectional magnetic

C. As a second anode and to prevent the build-up of secondary field

D. All of these