A signal generator is the one piece of test equipment that every lab relies on, yet its output quality is often taken for granted. I have watched engineers spend days chasing a circuit bug that turned out to be a noisy generator output. The moment you stop trusting your source, you stop trusting every measurement after it.
The reality is that signal generators drift, distort, and introduce spurious content in ways that are not always obvious on a quick oscilloscope check. Understanding what causes those errors—and how to fix them—saves hours of wasted troubleshooting.
Where Signal Generators Actually Fail
Most failures fall into three categories: amplitude errors, frequency drift, and spurious outputs.
Amplitude errors usually come from output attenuator wear. Mechanical step attenuators, common in older generators, develop contact resistance after thousands of cycles. The result is a level that is off by a few tenths of a dB—enough to throw off gain measurements or receiver sensitivity tests. Solid‑state attenuators solve this but introduce their own nonlinearities at low levels.
Frequency drift happens when the internal reference oscillator ages. A typical TCXO (temperature‑compensated crystal oscillator) drifts by 1–2 ppm per year. For a 1 GHz signal, that is 1–2 kHz of error. When you need to hit a narrow filter passband, that drift can mean your test signal lands entirely outside the device under test’s response.
Spurious outputs come from power supply noise, internal clock harmonics, or poor shielding. A spurious signal at –60 dBc might not bother a broadband measurement, but for a receiver sensitivity test, that spur can desensitize the front end and give you a false pass/fail result.
Product Introduction: A Signal Generator Built for Real Labs
A properly designed signal generator starts with a clean reference. Look for a unit that uses an oven‑controlled crystal oscillator (OCXO) rather than a basic TCXO. An OCXO holds frequency to within ±5 ppb over temperature—two orders of magnitude better than a standard TCXO. For applications that require external synchronization, a 10 MHz reference input and output allow you to lock multiple generators to a common rubidium or GPS‑disciplined source.
The output stage matters just as much. A modern signal generator should use a solid‑state leveling loop with closed‑loop power detection. This corrects for attenuator errors and temperature drift in real time. Output level uncertainty should be below ±0.5 dB from –120 dBm to +10 dBm across the full frequency range. Electronic step attenuators with 0.1 dB resolution give you fine control without the reliability issues of mechanical switches.
Phase noise is the hidden spec that separates lab‑grade from hobbyist gear. At a 20 kHz offset from a 1 GHz carrier, phase noise below –140 dBc/Hz is the threshold for serious RF work. This matters for testing narrow‑band receivers, radar systems, and any application where close‑in noise masks weak signals.
Sweep functionality should be flexible, not an afterthought. A good generator offers linear, logarithmic, and list sweeps with programmable dwell times. Triggering options—external, internal, or manual—let you synchronize sweeps with other test equipment. For automated test systems, GPIB, Ethernet, and USB interfaces should all be available, with a documented command set that matches industry standards.
Finally, the user interface matters for efficiency. A physical numeric keypad and a rotary encoder are faster for frequent parameter changes than touchscreens alone. Save/recall registers for common setups reduce setup time and eliminate manual entry errors.
When you feed a clean, stable signal into your device, you trust the result. That trust starts with a signal generator designed for repeatability, not just specs on a datasheet.
For more information, visit Jetronl’s website: https://www.jetronlinstrument.com/.