  The broadband emission observed from radio galaxies, BL Lac objects and
quasars is thought to be produced by energetic electrons confined in plasma
blobs which are ejected from supermassive black holes at relativistic speeds.
The lower energy radio-through-optical component is almost certainly nonthermal
electron synchrotron radiation, while the higher-energy $\gamma$-ray component
is probably due to Compton scattering of target photons by these same
electrons. If the high-energy component is formed by jet electrons
Compton-scattering radiation from outside the jet, such as the direct or
rescattered accretion-disk photons, then the ratio of the power in the
high-energy Compton component to the power in the low-energy synchrotron
component stands in a simple relation depending on the observing angle to the
jet and the plasma outflow speed. When combined with contemporaneous VLBI
measurements of apparent transverse speed, we find that a simple diagram
relates different classes of radio-loud active galactic nuclei (AGNs) and makes
definite predictions for multiwavelength observations of these sources. If an
equipartition parameter remains constant between episodes of plasma ejection,
then multiple observations of a single source can in principle determine the
Hubble constant.
