Fundamental vs 3rd Overtone

Typically when we talk about crystals, we are referring to crystals using the fundamental vibration mode of AT-cut quartz.  Simply stated, “fundamental vibration mode” refers to the crystal resonating at the frequency it is ‘designed’ for.  Fundamental resonant frequency is inversely proportional to thickness, which can cause issues at higher frequencies.  Fundamental-mode crystals at frequencies higher than 50 become very expensive as the quartz blanks are extremely thin and difficult to handle.  This causes the crystal to have a higher rate of breakage in processing.  It is for this reason that at higher frequencies, most crystals will be designed to operate on a crystal’s 3rd overtone.

A 3rd overtone-mode crystal resonates at three times its fundamental frequency.  There are in fact an infinite number of odd number harmonics that exist on the same quartz plate.  The first, third and fifth harmonics are shown in the figure below.  You might notice that there are some anharmonic modes or spurs shown in between, which are by-products of other vibrational states.  These unwanted modes may be suppressed sufficiently by providing a large enough plate diameter to electrode diameter ratio, or by contouring (i.e., generating a spherical curvature on one or both sides of the plate).

As previously discussed, quartz crystals have an equivalent circuit of a series RLC for the fundamental and each harmonic mode, plus a capacitor in parallel representing the capacitance of the electrodes.  The resistance for a third overtone crystal is more than three times that of the fundamental mode, while its capacitance is almost nine times less.  These changes greatly affect the Q and tunability of the crystal.  Third overtone crystals have better stability performance (higher Q), however are significantly more difficult to tune.  This also explains why in oscillators with compensation circuitry (VCXO/TCXO/OCXO) using third overtone and higher crystals are avoided.

Read more here:

OX–304 10MHz Ultra Low Phase Noise OCXO with Reduced Footprint

The OX–304 is a 10MHz Ultra Low Phase Noise Ovenized Crystal Oscillator with a noise floor as low as –173 dBc/Hz in a compact 20mm x 20mm x 15mm enclosure. Designed for applications that demand extremely low noise sources, including the reference oscillator for a phase–locked loop in the microwave spectrum. Custom frequencies available upon request.

Key Features: 

Product OX-304
Frequency Range 10 MHz
Size 20 x 20 x 15mm
Outputs Sinewave
Phase Noise, 10 Hz -135
Phase Noise, 100 Hz -150
Supply 12 V

OCXO Application Note
Additional Information


  • -135 dBc/ Hz at 10 Hz offset
  • -173 dBc/Hz at 10 kHz offset
  • 10 MHZ standard, other frequencies available
  • Compact 0.8” x 0.8” hermetic enclosure


  • Military Radar
  • Instrumentation and Test Equipment
  • Synthesizers
  • Military Communication Equipment
  • DRO reference
  • Satellite Communications

The TX–321 Low Noise TCXO achieving a close–in phase noise of −116dBc/Hz@10Hz and a floor of –165dBc/Hz


The TX-321 is a low g-sensitivity, low phase noise, dual crystal temperature controlled Oscillator packaged in a 23 x 18 mm footprint. With a frequency range of 10 to 50 MHz, and a phase noise performance of -116dBc/Hz @10Hz offset and a floor of -165dBc/Hz, making this TCXO is ideal for harsh environment military and industrial applications.

Key Features: 

Product TX-321
Frequency Range 5.0 to 50.0 MHz
Size 23.0 x 18.0 mm
Outputs HCMOS | Sinewave
Phase Noise, 10Hz -116dBc/Hz
Phase Noise, Floor -165dBc/Hz
Supply Voltages 3.3 or 5.0 V


  • Frequency range: 5 to 50MHz
  • Phase Noise: −165dBc/Hz @100kHz offset
  • Temp Stability: ±1ppm, −40°C to 85°C
  • g–sensitivity: <0.2ppb/g typical
  • Package: 23 x 18mm FR4 based SMD
  • Output: HCMOS, Sinewave
  • Supply: 3.3 or 5.0 V


  • Military Radio
  • GPS Telemetry
  • Test and Measurement Equipment

The VX–505, Extended Temperature Range (−55 to 125°C) High Frequency VCXO


The VX-505 Voltage Controlled Crystal Oscillator provides a phase noise floor as low as -166dBc/Hz across the extended temperature range of -55°C to 125°C with a wide frequency range of 20MHz to 800MHz.


• AT-Cut Crystal
• Surface Mount FR4 based package
• Refl ow Process Compatible
• Extended temperature range -55..+125°C
• Low Phase Noise
• Tight Stabilities
• Frequency Range 20 – 800MHz
• Standard Frequencies 20; 30,72; 32,768; 38,88; 44.8;
61.44; 76.8; 77.76; 81.92; 92.16;100; 112; 122.88; 125;
134.4; 153.6; 155.52; 160; 179.2; 184.32; 195; 208; 245.76;
320; 368.64; 400; 448; 491.52; 640; 672; 737.28; 800MHz


• Communication
• Industrial
• Harsh Environmental
• Military


The HX–171, Industry First 150°C High Stability Oven Controlled Crystal Oscillator


The HX–171 High Temperature, High Stability Oven Controlled Crystal Oscillator offers aging performances of ±1.5ppb/day with excellent temperature stability of ±5ppb across the extended temperature range of −40°C to 150°C.



  • Frequency: 10 or 20MHz (other frequencies available)
  • Temperature range: −40°C to 150°C
  • Temperature stability: ±5ppb
  • Package: 38 x 28 x 23 mm
  • Output: HCMOS
  • Supply: 5.0 V
  • RoHS compliant
  • EAR99
  • Made in USA


  • Oil/Gas downhole tool
  • High temperature industrial process control
  • Extended temperature Military/Aerospace
  • Avionics

The VS–507 High Frequency VCSO with Ultra Low Jitter (10fs–rms) Performance


High Frequency Ultra Low Jitter SAW Oscillator

The VS-507 is the latest addition to our ultra low jitter Voltage Controlled SAW Oscillator family. Packaged in an industry standard 14.0 x 9.0 mm footprint, this VCSO offers a jitter performance of 10fs-rms over the offset bandwidth of 12kHz to 20MHz, across a high frequency range of 3.0GHz to 6.0GHz. This product is ideal for emerging Optical Transport networks as well as the next generation 5G wireless networks that demand a low jitter high frequency reference clock.


  • Frequency range: 3.0 to 6.0 GHz
  • Jitter: 10fs-rms (fN=5.89824, 12kHz to 20MHz)
  • Output: Sinewave
  • Package: 14.0 x 9.0 mm
  • Supply: 3.3 V


  • 5G Base Stations
  • 100G & 400G Coherent Receivers
  • High Speed Converters
  • Test & Measurement Equipment

Expansion of Extended Temperature OCXOs


The OX-400/401 and the MD-403 are the latest additions to the OCXO extended temperature range product family. Stabilities of +/-5ppb (OX-400/401) and an uncorrected stability of +/-10ppb (MD-403) are achieved while operating across a temperature range of -40 to 95oC. These OCXOs are ideal for applications in uncontrolled environments where operating temperatures can exceed the industrial temperature range.


  • Temperature range: -40 to 95oC
  • Frequency range: 10 MHz to 40 MHz
  • Temperature stability: +/-5ppb (OX-400/401)
  • Temperature stability: +/-10ppb (Uncorrected MD-403)
  • Supply: 3.3 V


  • Base Stations
  • Test Equipment
  • Military Communication Equipment

Space VCXO Hi–Rel Standard Now Released, Origination of DOC206218, Rev A

Origination of DOC206218, Rev A


  • Package: 9 x14mm J-lead SMT
  • Frequency range: 1MHz to 85MHz
  • Supply: 3.3V or 5.0V
  • Absolute pull range: as wide as +/-50ppm
  • Excellent phase noise performance
  • Utilizes a 4-point crystal mount
  • Radiation tolerant to 100krads (Si) TID


  • Manned space flight
  • Deep space exploration
  • Defense satellites
  • Commercial satellites
  • Scientific satellites
  • Ground based ICBM Silos
Hi–Rel Voltage Controlled Crystal Oscillators (VCXO)
Space Model # Package Style Output Frequency Range Available Input Voltage Output Waveform Absolute Pull Range (2) Temperature Range
5219/5221 16 Lead Flatpack 80 MHz to 200 MHz 3.3V LVDS ±20ppm –40°C to +85°C
5319/5321 16 Lead Flatpack 100 MHz to 320 MHz 3.3V LVPECL ±20ppm –40°C to +85°C
9 x 14 mm J Lead 1 MHz to 85 MHz 5.0V or 3.3V ACMOS ±50ppm –40°C to +85°C
VX–209 16 Lead Flatpack 10 MHz to 200 MHz 15.0V Sine ±50ppm –40°C to +85°C
VX–189 24 Lead Flatpack 201 MHz to 500 MHz 15.0V Sine ±50ppm –40°C to +85°C
(1) Model 5116 replaces previous Model VX–509

(2) Absolute Pull Range (APR) is the minimum guaranteed amount the VCXO can be varied from the center frequency. It accounts for degradations due to temperature aging, power supply and load variations.

The OX–407 Low g–sensitivity (0.07ppb/g) OCXO in a compact 14x20mm DIP package

The OX–407 Low g–sensitivity Oven Controlled Crystal Oscillator is housed in a compact 14x20mm dual inline package with g–sensitivity performance as low as 0.07ppb/g. Covering the frequency range of 10MHz to 50MHz and a phase noise floor of –150dBc at 100kHz offsets, this OCXO provides design engineers with limited board space a small form factor alternative without sacrificing overall performance in their design.


Key Features:

Product OX-407
Frequency Range 10 MHz to 50 MHz
Size 14 x 20
Outputs CMOS, Sinewave
Phase noise, 10 Hz -84
Phase noise, 10 kHz -145
Supply 3.3, 5.0 V


OCXO Application Note
Additional Information


The VS–708 High Frequency VCSO with Ultra Low Jitter (55fs–rms) Performance

The VS–708 ultra low jitter voltage controlled SAW oscillator is packaged in an industry standard 5.0 x 7.5 mm footprint. This VCSO offers a jitter performance of 55fs–rms over the offset bandwidth of 12kHz to 20MHz, with a frequency range of 600MHz to 2.3GHz.

VS-708 Photo


  • Frequency Range: 600MHz to 2.3 GHz
  • Ultra low jitter: 55fs–rms (fN=1.8GHz, 12kHz to 20MHz)
  • Absolute pull range: ±50ppm
  • Output: LVDS, LVPECL, Differential Sinewave
  • Package: 7.5 x 5.0 x 2.0 mm
  • Supply: 3.3 V
  • Tri-State output enable (OE, OS, OD)


  • High speed data converters (ADC / DAC)
  • Optical transport (40G / 100G / 400G)
  • Wireless communication
  • Cable modem termination systems (DOCSIS)