Switching time is not settling time
The two phrases are often used interchangeably, and the difference matters. Switching time is the interval from the command to change frequency until the source begins producing the new frequency. Settling time is the longer interval until the output is actually usable, meaning the frequency has converged to within a stated tolerance and the amplitude has stabilized. A source can report a fast switching number and still be unusable for a measurement until settling completes.
A meaningful agility specification therefore states both the time and the tolerance: settled to within a given frequency error and a given amplitude error. When you compare two sources, confirm that the numbers are quoted against the same settling criteria. A 5 microsecond figure measured to a loose tolerance is not equivalent to a 5 microsecond figure measured to a tight one.
What sets the limit
The dominant limit on switching speed in a synthesized source is the phase-locked loop. After a frequency command, the loop must reacquire lock, and the loop bandwidth governs how quickly that happens. A wider loop settles faster but tends to admit more close-in phase noise, so there is a direct tension between agility and spectral purity. Designers manage this with multi-loop architectures, direct digital synthesis, and dedicated fast-tuning paths.
This is why agility is usually offered as an option rather than a fixed property. The standard configuration favors a clean spectrum. A fast-switching option, often labeled FS, and an ultra-fast option, often labeled UFS, reconfigure the tuning path to settle in microseconds or even hundreds of nanoseconds. Some sources add a dedicated fast control port that bypasses the normal command parser to shave latency off every step.
Why agility matters: radar, EW, ATE
In radar, frequency agility is a survival feature. Hopping the carrier pulse to pulse spreads energy across the band, making the emitter harder to detect and harder to jam. The source has to land on each new frequency, settled and clean, inside the pulse repetition interval. If settling eats into the dwell, range and Doppler performance degrade.
In electronic warfare, a threat-simulation or jamming scenario may require the source to reproduce an agile emitter that retunes thousands of times per second. The faster and more deterministic the switching, the more faithfully the scenario is reproduced. Slow or jittery switching limits how dense and how realistic a threat environment can be.
In automated test equipment, switching speed is money. A production line that measures a device at dozens of frequencies multiplies every microsecond of settling by the number of points and the number of units. Cutting settling from hundreds of microseconds to a few microseconds can lift throughput substantially without touching anything else on the line.
How Berkeley Nucleonics sources compare
The table summarizes representative switching figures and the options that enable them. As with phase noise, confirm the exact settling criteria against the current datasheet before committing to a timing budget.
| Model | Frequency range | Switching speed | Fast option | Notes |
|---|---|---|---|---|
| 825-M | 8 kHz to 20 GHz | 5 µs (option FS) | FS plus Fast Control Port | FCP achieves under 10 µs per step; up to 4 phase-coherent channels |
| 805-M | 100 kHz to 22 GHz | 500 µs standard; 20 µs (option FS) | FS | Sub-microsecond phase control cited; compact module |
| 875 | 10 MHz to 40 GHz | 200 ns (vector path); under 2 µs (option UFS) | UFS | Vector source; 200 ns applies to modulation switching |
Choosing the right agility
Start from the dwell or test budget, not the headline number. Decide how settled the output must be, then work backward to the switching figure and the option that delivers it. For a multi-emitter EW scenario or a fast scanning radar, ultra-fast switching and a dedicated control port earn their keep. For a calmer measurement, the standard configuration keeps the spectrum cleaner and the cost lower.
To match a source and its fast-switching options to your dwell, test rate, or threat density, contact Berkeley Nucleonics at info@berkeleynucleonics.com or 800-234-7858. The full family overview is on the RF & Microwave Signal Generators documentation page.