Almost all devices now use the popular Universal Serial Bus (USB) interface for connecting and transferring data to and from other devices. Even laboratory devices are now available with the USB as their main interface to computers. Now, users can control frequency synthesizers also through the USB interface. Although neither the performance nor the features they offer are anywhere near those that bench top instruments provide, USB controlled synthesizers have their advantages. USB controlled synthesizers, although providing basic functions only, are far cheaper, requiring only a computer and software to operate. They are easy to handle, being mostly plug-and-play, have a tiny footprint, and yet, some of them operate beyond 25 GHz, with ultra-low phase noise. Here is a review of some of the popular synthesizers.

Pasternak Synthesizers

The synthesizer family, PE11S390X from Pasternak Enterprises, is USB-2.0 controlled. These lab or desktop type instruments collectively cover a frequency range of 25 MHz to 27 GHz, and are useful in combination with other instruments for testing equipment during their design and development phases. As they are extremely compact, engineers can use them virtually anywhere, even while testing and conducting measurements in the field.

The accompanying USB cable supplies control and power to the synthesizer from a laptop, which also doubles as the measurement interface. The synthesizer connects to the device under test through an accompanying coaxial cable with a male MMCX connector on one end and a female SMA connector on the other.

The PE11S390X family consists of six models, with the low end in the group covering 35 MHz to 4.4 GHz, and the high end covering the range of 24 to 27 GHz. At an offset of 100 kHz, the various models have a phase noise ranging from -75 dBc/Hz at 27 GHz to -103 dBc/Hz at 4.4 GHz. Users can adjust the output power from -20 to +18 dBm, in steps of 1dB.

Although the synthesizers operate from an internal clock of 50 MHz, users can operate them from an external reference between 10-70MHz. Other features available are synchronization to other test instruments, with LEDs indicating the USB connection, PLL lock, and RF power output. Users have the choice of controlling the synthesizers through Windows, Mac, or Linux platforms, and each has its own non-volatile memory for storing the last setup. All units operate from 0°C to +55°C.

Fairview Synthesizers

The USB controlled, phase locked loop (PLL) frequency synthesizer family from Fairview Microwave Inc. offer high levels of signal integrity, superior frequency stability and accuracy, and exceptional phase noise characteristics. Fairway family of synthesizers is useful or applications involving bench top test and measurements of microwave radios, signal generators, and equipment involved with electronic warfare.

With the GUI command control and DC power coming through USB-2.0 connectors from a PC or laptop, these rugged and compact synthesizers cover a broad range of frequency bands from 25 MHz to 27 GHz. Users can control the power output up to +19 dBm and adjust it down by 50 dB in 1 dB steps. With phase locked loop speeds of 1ms, the synthesizers offer phase noise as low as -108 dBc/Hz at an offset of 100 MHz.