A frequency standard is a stable oscillator for frequency calibration. A frequency standard generates a Specified frequency with a high degree of accuracy and precision.
Frequency standards are sometimes designated as primary or secondary. There are various Frequency standards are available.
Quartz Frequency Standard
Quartz Frequency Standard has been designed to provide a highly stable and spectrally pure frequency reference for applications requiring the ultimate in short term frequency performance. Ideal for laboratory or system use, provides good stability performance at lower cost and with improved phase noise. A Quartz crystal oscillator is an electronic circuit that uses the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency.
Temperature Compensated Xtal Oscillator (TCXO)
This is the oscillator used within a basic GPS Time and Frequency Receiver and delivers good performance for many applications not requiring enhanced level of stability or phase noise specifications.
Oven Controlled Xtal Oscillator (OCXO)
A much higher performance component that provides improved short term stability (approximately 10 to 15 times better at 100 seconds) and much improved phase noise. Ideal for applications such as HDTV Broadcasting, Satellite Communications Systems, mobile WiMax, and high performance frequency references.
A rubidium standard is a frequency standard in which a specified hyperfine transition of electrons in rubidium-87 atoms is used to control the output frequency. A rubidium standard consists of a gas cell, which has an inherent long-term instability. This instability relegates the rubidium standard to its status as a secondary standard. A good GPS time and frequency receiver utilizing a high performance internal rubidium oscillator can provide results equal to or better than a stand alone cesium standard.
A caesium standard is a primary frequency standard in which electronic transitions between the two hyperfine ground states of caesium-133 atoms are used to control the output frequency.
Hydrogen maser, a Hydrogen frequency standard, is a specific type of MASER (Microwave Amplification by Stimulated Emission of Radiation) that uses the intrinsic properties of the hydrogen atom to serve as a precision frequency reference. Both the proton and electron of a hydrogen atom have spins. The atom has a higher energy if both are spinning in the same direction, and a lower energy if they spin in opposite directions. The amount of energy needed to reverse the spin of the electron is equivalent to a photon at the frequency of 1,420,405,752 Hz. This 1420 MHz frequency is important in radio astronomy because it corresponds to the 21 cm line of interstellar hydrogen. Hydrogen masers are very complex devices. They are made in two types, active and passive.