Why Your Signal Generator Is a Time Bomb (And How a Rohde & Schwarz Arbitrary Waveform Generator Fixes It)

You don't need a better signal generator. You need a more predictable one.

If you're chasing the latest specs—wider bandwidth, higher sample rate, lower harmonic distortion—you're probably looking at the wrong problem. In my role coordinating test equipment for aerospace and defense projects, I've seen more projects delayed by unpredictable instrument behavior than by lack of raw performance. The real question isn't how good is your signal generator? It's can you trust it to do what you need, every time, under the conditions you can't control?

Here's the thing: most engineers treat signal generators as black boxes. They plug in parameters, hit generate, and assume the output matches the setting. In practice, especially when you're working with complex modulation schemes or non-standard waveforms, that assumption fails more often than you'd think. I've learned this the hard way—on at least four separate occasions in the past three years where a project's timeline hung on whether a generator could deliver what its datasheet promised.

What I've learned from 200+ emergency test scenarios

In March 2024, a client called at 5 PM needing a custom OFDM signal for a satellite test the next morning at 10. Normal turnaround for generating and validating a new waveform is about a week. We had maybe 10 hours, including overnight testing. We used a Rohde & Schwarz SMW200A vector signal generator—not because it had the highest specs on paper (though it does), but because we knew the ArbConfig tool would let us import an arbitrary waveform without hitting hidden filters or digital pre-distortion that could alter our intended shape.

I've tested 6 different signal generator families in rush scenarios. Here's what actually works: a generator that lets you bypass the internal signal optimization and inject raw I/Q data directly. That's where Rohde & Schwarz's arbitrary waveform generators—especially the SMBV100B and SMW200A—separate themselves. Their baseband generator mode gives you direct access to the DAC, bypassing the built-in correction algorithms that often introduce phase discontinuities.

Look, I'm not saying every standard signal generator is bad. But if you've ever cursed a generator for introducing unexpected spurs or glitches during a critical measurement, you already know the pain. The problem is structural: most generators optimize for common telecom waveforms. When you push outside those bands—custom modulation, non-linear sweeps, pulsed signals with fast edges—the internal processing can introduce artifacts that take hours to debug.

The three ways a generator can ruin your week

1. Hidden digital pre-distortion. Many generators assume you want a 'clean' signal. So they apply digital filters to reduce noise and improve EVM. That's great if you're testing a standard LTE transmission. It's a nightmare if you're trying to generate a radar pulse with a specific rise time, because the filter will smooth it out.

2. Phase discontinuities at waveform boundaries. When looping an arbitrary waveform, some generators introduce a phase jump at the loop point. This creates a spectral spike that can trigger false alarms in an EMI test. With the Rohde & Schwarz ARB mode, you can force continuous phase across loop boundaries. It's a small detail that makes a huge difference.

3. Unpredictable latency in frequency sweeps. If you're generating a frequency sweep for an automated test, you need to know exactly when each frequency step occurs. Some generators introduce variable latency based on DSP load. The R&S ARB generator bypasses that by using a deterministic time base.

People think expensive generators are just about lower noise floor and higher bandwidth. Actually, the real value is in being able to predict exactly how the instrument will behave in every scenario. The causation runs the other way: Rohde & Schwarz can charge a premium because they've eliminated the variables that cause project delays.

The specific model that's saved me (and my deadlines)

If you're looking at Rohde & Schwarz signal generators, here's what I'd actually buy:

• For general-purpose RF testing: The SMBV100B. It's compact, has excellent phase noise, and the ARB mode is well-implemented. If you're mostly doing standard comms testing but occasionally need custom waveforms, this is the sweet spot.
• For complex modulation and MIMO: The SMW200A. It's more expensive, but it has dual baseband generators and can combine them with extremely low inter-channel phase noise. If you're testing phased-array antennas or 5G NR with carrier aggregation, this is the one.
• For on-a-dime budgets: Consider the SMA100B for pure analog RF performance. It doesn't have arbitrary waveform capability, but if you need a super-clean sine wave for a reference, it's hard to beat.

Of course, Rohde & Schwarz isn't the only player. Keysight's MXG series has excellent phase noise as well, and Anritsu's MG3710A has strong multi-format capabilities. But from my experience, when you're looking for predictability—the ability to know that the generator will do what you need on the first try, every time—Rohde & Schwarz wins.

When you don't need a Rohde & Schwarz signal generator

Honestly, I'm not sure why some engineers insist on buying premium generators for every bench. My best guess is it comes down to habit and budget leftovers. Here's when you can go cheaper:

• You're only testing standard, unmodified waveforms (CW, AM, FM, standard LTE/5G NR).
• Your test sequence can tolerate a ±5 dBm output power error without failing the DUT.
• You have time to validate the generator's actual output against a spectrum analyzer before each major test.

If those conditions hold, a mid-range generator from Rigol or Siglent might be fine. But in my experience, even supposedly 'simple' tests—like characterizing an LNA's gain compression with a swept CW signal—can uncover generator flaws. I once spent 2 hours chasing a 0.3 dB gain variation that turned out to be the generator's automatic level control (ALC) struggling at low frequencies.

The 'always buy the most expensive' advice ignores budget constraints and the law of diminishing returns. For repetitive production tests where the waveform is fixed and has been validated, a cheaper generator might be the better business decision. But for engineering labs—where you're constantly trying new things and running into edge cases—the predictability of a Rohde & Schwarz generator pays for itself in saved debug time within the first few months.

Final decision framework (take it from someone who's been burned)

If you're weighing options and you've read this far, here's the quick matrix I use:

• Project type: R&D prototype / custom waveform testing → invest in R&S ARB capability
• Project type: Production / fixed-format testing → consider mid-range generator
• Time pressure: Tight deadlines (under 2 weeks /generator validation) → buy the R&S to avoid surprises
• Time pressure: Flexible timeline / can validate instrument → lower-cost option is viable
• Team expertise: Experienced RF signal chain expert → can handle any generator's quirks
• Team expertise: Junior engineer / heavy reliance on 'black box' → better to remove uncertainty with R&S

I'd rather spend 10 minutes explaining which generator to buy than deal with a failed test the day before a customer demo. An informed buyer asks better questions and makes faster decisions. That's what I'm hoping you'll do here: stop looking at spec sheets and start asking 'What happens when I need to generate a signal that doesn't match any preset?' Because that's when the $6,000 generator becomes a $12,000 problem—and the $30,000 generator becomes a bargain.