A crystal oven is a sealed environment placed around a quartz crystal in high-precision devices. These ovens maintain a constant temperature and pressure, insulating the internal crystal from environmental changes. Generally, a crystal oven is only used on extremely high-precision devices, such as military-grade radio systems and cellular towers. On lower precision devices, the benefit is far out shadowed by the cost and potential bulk of the device.
When a quartz crystal is used as a resonator in a device, it is a major part of sending and receiving signals. The resonance frequency of the quartz is used to tune the transmitter, keeping the sent signals stable. The frequency of the quartz is determined by several factors, including the size of the crystal. As the quartz warms and cools, it can expand and contract. This results in tiny size changes, which change the crystal’s frequency.
Devices that can’t afford to have fluctuation in frequency use a crystal oven to keep the crystal stable. By keeping the crystal’s situation stable, regardless of the actual conditions, its frequency never changes. The most common form of crystal oven is used inside a crystal oscillator.
A crystal oscillator is a common component found in precision measuring instruments, transmitters and receivers. These devices can be very small, and are often incorporated directly into a device’s circuitry. When a crystal oven is used in these devices, it is usually a non-powered insulating device. It relies on its mechanical construction to keep the crystal stable.
Other devices have larger ovens that work on a totally different scale. These devices are built as sealed canisters containing their own stable environment. These ovens often require external power and specially constructed crystals. While this type of crystal oven may be much larger than the oscillator version, some versions are still small enough to connect directly to a circuit system.
In most cases, crystal ovens are unnecessary. On common electronic devices, the degree of precision given by a crystal oven is far more than the user requires. That, along with the added cost of building them into the device, makes many manufacturers skip them in their designs.
On the other hand, they are needed when users require a very high level of precision or stability. On a consumer level, this is usually found in high-end watches, diagnostic tools and audio equipment. On a commercial level, local transmission hubs such as cellular towers or radio transmission stations use these ovens to keep their frequencies within the correct bandwidth. Finally, military systems use these ovens to keep transmission bands narrow to prevent unwanted bleed into adjacent frequencies.