Hertz

The hertz is a unit of frequency, named after Earth scientist Heinrich Rudolf Hertz. One hertz is equal to one cycle per second.

Comparative list of frequency

The EM pattern given off by the Sentry on one of the moons in the Pentarus system remained between 5 and 15 hertz when the water fountain it protected was unthreatened. When the fountain was approached, the Sentry's frequency would rise to 40 hertz. (TNG: "Final Mission")
In 2375, The Doctor sang up to a range of 880 hertz in order to check for damage to Chakotay's auditory nerves. This was done after exposure to chaotic space had reactivated a previously suppressed gene that caused, among other symptoms, auditory hallucinations. (VOY: "The Fight")

When the USS Voyager used a microprobe as a subspace communications relay to contact a Romulan science vessel through a micro-wormhole, B'Elanna Torres noted that the phase amplitude of the visual link with the ship was within a few megahertz of transporter protocols. (VOY: "Eye of the Needle")
While manually conducting a lateral scan aboard the disabled USS Defiant, Major Kira noted that the sensors were set at 15 megahertz for their range of five hundred kilometers. (DS9: "For the Uniform")
Arik Soong had Enterprise adjust its scanning frequency to 15 megahertz to located the Augments stolen Klingon bird-of-prey. (ENT: "The Augments")
The frequency modulation for the shields of USS Enterprise-D, prior to its destruction in 2371, was 257.4 megahertz. When the Duras sisters discovered this frequency, they adjusted the frequency of their weapons, allowing them to directly impact the Enterprise's hull. (Star Trek Generations)
George and Gracie were tagged with the radio frequency was 401 megahertz prior to their journey from the Cetacean Institute to their release into the wild. (Star Trek IV: The Voyage Home)
The frequency in the message transmitted by V'Ger was sent at a rate of one million megahertz and lasted only a millisecond. At that high rate of speed, the message was initially undetected. (Star Trek: The Motion Picture)

1 million megahertz is actually equal to 1 terahertz.

Hand phasers set to a dispersal frequency of 1.85 gigahertz were able to penetrate the Voth cloaking technology. (VOY: "Distant Origin")
Subspace warheads encounter by Voyager in 2377 had an activation frequency of 4.84 gigahertz. (VOY: "Human Error")
In 2373, the swarm hit Voyager with a polaron burst that changed the deflector shield polarity, causing it to rotate at 92 gigahertz. (VOY: "The Swarm")
By increasing the warp plasma 97 gigahertz, Miles O'Brien could increase the velocity of the USS Defiant to warp 9.5. (DS9: "The Sound of Her Voice")
The subspace communications frequency utilized in Earth Starfleet communications is 384.20 gigahertz. (ENT: "Shadows of P'Jem", "Shockwave", "Cease Fire")

The attack by Voyager on Tactical Cube 138 in 2376 created a 0.06 terahertz fluctuation in the cube's ventral shield grid, enough to allow a team aboard the Delta Flyer to beam aboard. (VOY: "Unimatrix Zero")
In 2374, during an attempt to beam deuterium from beneath a Class Y planet's surface, Voyager's transporter's annular confinement beam was narrowed to .47 terahertz. (VOY: "Demon")
327 systems that used terahertz feeds were known to the Federation in 2267, none of which were used by Starfleet. (TNG: "The Mind's Eye")
The forged Federation phaser rifles created by the Romulans, discovered on Krios Prime and used by Kriosian rebels, were charged with a forced pulse, well into the terahertz range. This range is similar with those found in Romulan disruptors, which create an inverted initial output spike, with corresponding discharge crystal and emission beam pattern. (TNG: "The Mind's Eye")
Geordi La Forge's VISOR operating frequencies were between 1 Hz and 100,000 THz. (TNG: "The Masterpiece Society")
A gamma scan conducted by the crew of the Enterprise-D in 2368 had a composite frequency of 2.43 × 10²² hertz. (TNG: "Silicon Avatar")