Secondary Features to Analyze When Choosing Programmable Digital Signal Generators for Your RF/microwave Test Sets

Posted on Monday, May 13, 2019

This blog is the second part of helping you gain an understanding of the features and flexibility to look for in a self-programmable signal generator so you can align your desired ATE outcomes with the total budget you have for your bench or rack system. Here we will explore Frequency Switching Speed, Output Power Range, Harmonics, Non-harmonic Spurious Content, Modulation, and Connectivity/Control. If you missed it, don't forget to check out Part 1 on Frequency Range, Resolution, and Phase Noise.

 

Frequency Switching Speed

The frequency switching speed of a signal generator dictates how swiftly that device can jump from one frequency to another. Certain frequency agile radar, frequency hopping wireless standards, and other multi-band wireless devices require the ability to rapidly adjust frequencies and a signal generator will need to perform similarly to aid in prototyping and testing of such systems. 

 

The frequency switching speed of a signal generator depends on the signal generator control and tuning technology, and is often different for manual control, programming, and external control configurations. For external control and programming frequency switching speed, Lab Brick’s Signal Generators exhibit among the fastest speeds available, and generally cost much less than competitive models with switching speeds several times slower.

 

Output Power Range

Output power range is another signal generator parameter that is often over-purchased. In many applications, power levels beyond a few dB or below -20 dB will require precision amplifiers or attenuators to adjust the signal strength to the desired level. Some signal generators include these amplifiers and attenuators inline, which must be designed to cover the entire operation frequency of the device. For wideband signal generators this may require several different attenuator or amplifier paths, as attenuators or amplifiers that cover extremely wide frequency ranges exhibit performance trade-offs. These additional signal paths and related hardware lead to added noise, phase noise, complexity, size, and cost.

 

For a given application, it is more cost-effective, and also a higher performance solution, for an engineer to purchase discreet precision attenuators and amplifiers that better fit their frequency and performance requirements, as opposed to wideband that necessitates design and performance trade-off; some of which may not be transparent. 

 

Vaunix’s Lab Brick Signal Generators offer output power range performance that fits most applications and come at a price point that leaves plenty of room in the budget for precision accessories better optimized for a specific application.

 

Harmonics

Harmonics are a natural result of signal generation and are inevitable for all signal generator typologies. The power level of the second, third, and greater harmonics depend on the signal generator typology and how much filtering is applied to attenuate the harmonics. Reducing harmonic signal power comes with tradeoffs for other performance aspects, which may or may not be desirable. Most benchtop “one-size-fits-all” signal generators include additional circuitry to reduce harmonics to as low levels as possible across the entire operation frequency.

 

Though this approach allows a “good-looking” harmonic specification on a data sheet, it comes at significant cost. Harmonics can be readily filtered if a user has known frequency bands they will be using; harmonics affecting these bands can be accounted for as they occur at known frequencies at a function of the carrier frequency. Depending on the application, the harmonics may be outside of the bandwidth of concern or component/device operation, making an extremely low harmonic level across a wide frequency spectrum a moot point.

 

Reducing harmonic levels inherently leads to an increase in non-harmonic spurious signal content which can occur at unpredictable and inconvenient frequencies. Lab Brick’s Signal Generators are designed to exhibit both excellent harmonic performance and non-harmonic spurious performance at application specific bands.
Non-harmonic Spurious Content

 

Spurs are unavoidable signal purity contaminates that are an unpredictable function of a signal generator components. Spurs are often difficult to filter out, especially for signal generators that operate over a wide frequency range. To obtain superior non-?harmonic spurious performance from a benchtop signal generator, one typically has to purchase an additional option to meet those figures. This is not the case with Vaunix’s versatile line of Signal Generators.

 

Modulation

Even the latest radar systems use modulation to enhance performance. During RF and microwave system testing and prototyping, modulating signals is often the only way to determine real-world receiver and system component performance. Hence, most RF signal generators include analog modulation, vector modulation, sweep, or pulse modes. Generally, the analog modulation modes include AM, FM, PM, and sometimes analog IQ program or input modes. For vector modulation, an engineer typically needs to either buy an upgrade module, or a distinct vector signal generator. 

 

The modulation upgrades are often much more expensive than the base signal generator and may not include the modulation capability an application requires. However, the modulator circuits do not actually need to be part of the signal generator and can be purchased at reasonable prices separately. Combined with a low-cost Vaunix Lab Brick Signal Generator with pulse and sweep trigger options, a modular test/prototype system could be a much more cost-effective approach than purchasing and customizing an all-in-one benchtop unit.

 

Connectivity and Control

The most common signal generators are benchtop (or rack) units that have some sort of manual control based on knobs, buttons, and a display. Though familiar and time-tested, the size and form factors of these legacy signal generators require additional components, increase the device size and cost, and introduce potential failure modes. Manual-control signal generators are often not customizable, and sometimes difficult, or impossible, to program or operate externally, as external control and programming wasn’t the targeted focus of the design. 

 

Vaunix’s Lab Brick Signal Generators circumvent these problems by operating from universal USB cable for both power and control. They come with free and easy-to-use GUI software, unlike most other Signal Generators that require the purchase of proprietary software for external programming/control. Moreover, Lab Bricks are also programmable via LabView® software drivers from National Instruments®, and Lab Brick support software includes free 32-bit and 64-bit DLLs that provide comprehensive and easy to use API. This signal generator software enables the control of several Lab Brick signal generators from the same PC, which can allow a user to easily set up a multi-signal test or prototyping system.

 

Cost/Performance Ratio

The most common signal generators are benchtop (or rack) units that have some sort of manual control based on knobs, buttons, and a display. Though familiar and time-tested, the size and form factors of these legacy signal generators require additional components, increase the device size and cost, and introduce potential failure modes. Manual-control signal generators are often not customizable, and sometimes difficult, or impossible, to program or operate externally, as external control and programming wasn’t the targeted focus of the design. 

 

Vaunix’s Lab Brick Signal Generators circumvent these problems by operating from universal USB cable for both power and control. They come with free and easy-to-use GUI software, unlike most other Signal Generators that require the purchase of proprietary software for external programming/control. Moreover, Lab Bricks are also programmable via LabView® software drivers from National Instruments®, and Lab Brick support software includes free 32-bit and 64-bit DLLs that provide comprehensive and easy to use API. This signal generator software enables the control of several Lab Brick signal generators from the same PC, which can allow a user to easily set up a multi-signal test or prototyping system.

 

In Conclusion

Even in the most well-managed, cost-sensitive organizations today, you’ll still find test benches with expensive test boxes that are largely underutilized. But as the release of cost-efficient, self-programmable, and portable test instruments continues from Vaunix, a test engineer has the ability to now consider his/her bench in a new way. For many, it’s a dream come true. For others who’ve become comfortable with legacy systems, it’s a new learning experience. But for all, there are key features to look for from each instrument. By zeroing in on who offers you the most intuitive connectivity and control and figuring out what features are most critical within your desired frequency ranges, you’ll be ready to build a new RF/microwave test bench that suits your needs and budget perfectly.

 

Learn more by downloading our Tech Brief "10 Signal Generator Features You’re Probably Paying Too Much Forand by reviewing our complete line of RF/Microwave USB-programmable Digital Signal Generators.

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