Low-cost Universal Serial Bus (USB) radio frequency (RF) signal generators have recently come on the scene in the wireless world. They promise to be game changers for many reasons. Until these devices came out, a prospective buyer had two choices when it came to RF signal generation solutions. The buyer could either purchase a $20K+ benchtop box with all the bells and whistles, or they could purchase a $6K narrowband “synthesizer,” either hard coded to one frequency, or with an RS-232 programming port to figure out. Both of these solutions would typically take eight weeks to deliver. They are generally build-to-order components.
USB RF signal generators are actually a hybrid approach to both of those options mentioned above—they can be much cheaper and deliver in a couple of days. A great USA-made example is Windfreak Technologies’ SynthHD Pro Dual Channel Microwave Signal Generator for $1,979. This price is actually cheaper than some RF test cables.The device has two independent channels that can tune in 0.1 Hz increments from 54 MHz to 13.6 GHz. The SynthHD’s RF power is adjustable in .01 dB increments from -50 dBm to +22 dBm. It also has many modulation features including FM chirps. The relative phase between the two channels can be adjusted in .01 degree increments.
The SynthHD signal generator will generate sweeps. The sweeps can be single channel or dual channel. The device can sweep up or sweep down. It can also ramp up or down amplitude while sweeping. The sweep can be controlled with an external trigger to either perform a full sweep per trigger, or perform a single step. In dual channel mode, you can program a constant frequency offset between the two channels for the sweep.
The SynthHD signal generator will generate hops. The GUI allows the user to program up to 100 arbitrary points with a frequency and amplitude in dBm. This table is stored onboard in nonvolatile memory. Like the sweep mode, the user can then have an offset on the other RF channel, hop up the list, hop down the list, and work with the trigger input.
Additionally, the SynthHD signal generator will digitally modulate FM, AM, and pulse. FM can be a typical sinusoidal signal, or it can also be a chirp. AM can also be the typical sinusoid signal or it can be ramps. The modulations can be combined. Combining a pulse and a chirp allows the user to set up a frequency modulated continuous wave (FMCW) radar signal. You can even combine this with the sweep function. As an electronic warfare example, you could sweep a pulsed waveform across a range of frequencies. Rates can be very slow, or in the case of FM, up to 5 KHz. Of course, all of these features can be saved to the device. It will begin sweeping on power up without a PC connected!
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