Microwave, RF & LF Signal Sources & Sensor Systems

Spectral Line Systems Ltd

Research, Custom Design & Manufacture

Crystal Multipliers

100 MHz Ultra-Low Phase Noise VCXO

Photograph 1

Anti Vibration Mounted Low Noise Crystal Oscillator
Photograph 2
Anti Vibration Mounted 1.0 GHz Crystal Multiplier
Photograph 3
640 MHz Phase Locked Crystal Multiplier
Photograph 4
Two Channel Microwave Crystal Multiplier
Photograph 5

Crystal Multiplier Sources consist of a crystal oscillator (XO) followed by a frequency multiplier. Spectral Line Systems crystal multipliers are based on our long established series of ultra-low phase noise voltage controlled crystal oscillator (VCXO) designs. These designs are also available packaged as stand alone units, and can be supplied to the customer's specification of frequency, output power, supply voltage, tuning voltage range, packaging, etc. A 100 MHz version is shown opposite (photo 1), packaged for general use.


All oscillators based on piezo-electric crystals are by their nature subject to phase noise degradation by vibration and acoustic noise. This can be mitigated by anti-vibration mounting, as shown here (photo 2), and by building acoustic absorbers into the outer enclosure walls and covers.


For best phase noise performance above 100 Hz from carrier the oscillator frequency is normally chosen to lie in the range of approximately 75 to 130 MHz. Voltage tuning allows phase locking to a lower frequency reference signal (e.g. 10 MHz), to improve long term stability and phase noise in the sub 100 Hz from carrier region.


Multiplication of the crystal frequency to that of the desired output signal is normally based on either diode frequency doublers or step recovery diode (SRD) impulse generators. Doublers tend to be used for frequencies up to a few GHz, combinations of doublers and mixers sometimes being employed in order that any harmonic of the crystal frequency may be obtained. Photograph 3 shows a 1.0 GHz crystal multiplier implemented as 8 X 125 MHz, the unit being mounted on an anti-vibration suspended plate.


Photograph 4 shows a 640 MHz low noise crystal multiplier based on a 128 MHz VCXO. Auxiliary outputs are provided at 128 MHz and 512 MHz, and the 128 MHz VCXO is phase locked to an internal 10 MHz oven-controlled crystal oscillator (OCXO) via a low bandwidth loop for improved long term stability. Switching is provided to allow the use of an external 10 MHz reference if required.


Photograph 5 shows a 2-channel microwave crystal multiplier with a common output amplifier. The lower unit contains two independent switched crystal multiplier chains producing 1,000 MHz and 1,040 MHz from 125 and 130 MHz crystals. Harmonics of the 1000/1040 MHz signals are generated by a pair of coaxial SRD's and the desired harmonics at 12.0 and 12.48 GHz selected by waveguide coupled cavity band-pass filters and combined in the output amplifier.


The phase noise performance of a crystal multiplier unit can be theoretically predicted by increasing the oscillator noise by 20 log10 (multiplication ratio). In practice, the result will be degraded by the added noise of the multiplier. An oscillator of frequency 100 MHz with a noise floor of -170 dBc/Hz, for example, will result in a floor of around -127 dBc/Hz at 10 GHz.