This is not just a standard crystal. It has been specifically selected, tested, and optimized for high-performance RF applications.
The crystal is designed for use as a 133.3 MHz local oscillator (LO) in VHF receivers. When used with the standard 10.7 MHz intermediate frequency (IF), the receiver operating frequency is:

Receiver Frequency = LO Frequency + IF Frequency

144.0 MHz = 133.3 MHz + 10.7 MHz

For receiver local oscillator applications, phase noise and frequency stability are among the most critical parameters. This custom crystal provides exceptional performance with -163 dBc/Hz phase noise @ 10 kHz offset and ±10 ppm frequency stability, making it an excellent frequency reference for demanding RF applications.
In addition to receiver local oscillators, this crystal is also well suited for precision clock generation in DDS synthesizers (such as AD9850), high-speed DACs, ADCs, frequency converters, and many other RF systems requiring a clean and stable frequency source.
We have designed, built, tested, and optimized a complete oscillator circuit specifically for this crystal to achieve reliable startup, excellent frequency stability, ultra-low phase noise, and a clean RF output.

The supplied schematic is based on a 5th overtone Colpitts oscillator, carefully optimized for operation at 133.3 MHz.
Unlike many simple crystal oscillator circuits, our design includes a dedicated buffer amplifier. The buffer isolates the crystal oscillator from external load variations, preventing load-induced frequency pulling and preserving both frequency stability and phase noise performance.
The output is followed by a carefully designed low-pass filter (LPF) that suppresses unwanted harmonic components generated by the oscillator. As a result, the output signal has a clean spectrum with excellent harmonic suppression, making it suitable for sensitive RF applications.

Measured oscillator performance:

• Frequency: 133.3 MHz
• Supply voltage: 3.3 V
• Output power: 0 dBm (224 mVrms into 50 Ω)
• Oscillator topology: 5th overtone Colpitts
• Buffered output for excellent load isolation
• Low-pass output filter for harmonic suppression

Why the Crystal Frequency is 133.301 MHz

Although the desired operating frequency is 133.300 MHz, the crystal itself is intentionally manufactured at approximately 133.301 MHz.
This is done to compensate for the unavoidable parasitic capacitance introduced by the PCB layout, transistor junctions, component pads, wiring, and other circuit elements.
These parasitic capacitances naturally reduce the oscillation frequency by approximately 1…3 kHz, depending on the PCB layout and construction.
By intentionally ordering the crystal slightly above the target frequency, the completed oscillator settles very close to the desired operating frequency after installation. If you plan to order your own custom overtone crystals, we recommend specifying a frequency approximately 1…3 kHz above the desired operating frequency to compensate for these unavoidable parasitic effects.

Frequency Adjustment

Small frequency adjustments can easily be made within the oscillator circuit.
Increasing the inductance of L12 slightly reduces the oscillation frequency.
Decreasing the inductance of L12 slightly increases the oscillation frequency.
Additional fine adjustment may be performed using C19. A trimmer capacitor in the range of 10–30 pF is recommended.
However, reducing the capacitance too much may noticeably decrease the oscillator output level. For this reason, it is generally preferable to order the crystal slightly above the desired frequency and perform the final frequency adjustment using L12.

5th Overtone Operation

Most Colpitts crystal oscillators naturally operate either at the crystal’s fundamental frequency or on the 3rd overtone.
Operating reliably on the 5th overtone requires additional frequency selection.
In this design, L13 together with C29 forms a resonant network tuned to the desired overtone. This resonant circuit promotes oscillation on the 5th overtone while suppressing unwanted oscillation modes.
This is a simplified explanation of the oscillator’s operating principle.

Output Power Optimization

The oscillator was intentionally optimized to provide approximately 0 dBm (224 mVrms into 50 Ω).
This output level is more than sufficient for receiver local oscillators, DDS clock inputs, DACs, ADCs, frequency converters, and most other RF circuits.
If additional output power is required, R12 may be reduced to approximately 33 kΩ, increasing the output level to approximately +2 dBm.
Even higher output power may be achieved by increasing the buffer amplifier current or operating the circuit from a higher supply voltage (typically 5 V to 12 V). In this case, the transistor bias network and resistor values should be recalculated accordingly.

Ready-to-Build Reference Design

The published schematic has been thoroughly tested and optimized using this crystal.
When assembled with the specified component values, the oscillator starts reliably and operates as intended without requiring circuit modifications or manual tuning under normal construction conditions.
This reference design provides an excellent starting point for anyone requiring a high-performance, low-phase-noise crystal oscillator for professional or amateur RF applications.

Listing includes:

• Quartz Crystal Resonator 133.3 MHz – 1 pc

Quartz Crystal Resonator 133.3 MHz

General description:

Tolerance: 10 PPM
Type: UM-5
Load capacitance (CL): 20 pF