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Industry News / Test and Measurement

An RF Signal Generator Offering Full Digital, Vector and Analog Modulation

October 1, 2002
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The humble signal generator has come out of its modest, functional shell and taken on a streamlined, compact, state-of-the-art persona with the development of the 3410 series.


This family of digital RF signal generators has evolved in response to the worldwide growth of second- and third-generation wireless communications systems and the prevailing demand for products with digital modulation capabilities. The call is for RF signal generators that deliver wider baseband modulation bandwidth and improved dynamic range, provide more arbitrary waveform generator memory and run at greater speeds. Also, with many wireless formats having their own special characteristics, additional functionality is made available to the user.

To meet these needs there are currently three models in the series addressing the frequency ranges 250 kHz to 2 GHz (model 3412), 250 kHz to 3 GHz (model 3413) and 250 kHz to 4 GHz (model 3414). All three use the same housing.

Developed for testing and emulation of 2G, 3G and the emerging 4G systems, digital Private Mobile Radio (PMR), Wireless Local Area Networks (WLAN) and Bluetooth systems, this high performance digital RF signal generator family combines full digital, vector and analog modulation in a 2U rack size.

Both analog (FM, AM, phase and pulse modulation) and broadband vector modulation are standard, with a digital dual-channel arbitrary waveform generator (ARB) available as an option. Fitted internally and providing good modulation accuracy and linearity, the ARB is capable of generating 2G, 2.5G, 3G and PMR digital radio signals.

The added functionality and sophistication of the 3410 series is a serious development and is allied to simple operation and suitability for its intended users. To satisfy both seasoned RF engineers and new graduates from the PC generation, the design makes use of emerging technologies while retaining the traditional look and feel of a signal generator. It offers familiarity together with widely used international icons and symbols.

Keeping in Touch

Based on a compact touch-panel display system, with a keyboard control alternative that can be used simultaneously, the series provides an interface that is simple to use yet capable of controlling all the advanced features required for digital and vector modulation. The simplicity is epitomized by the fact that by using the touch-screen to combine the selection and indication process there is no need for dedicated function keys. As is consistent with those found so often in everyday life, the touch-screen adopts an action-on-release operation. As for the hard-key alternative, this facility enables the signal generator to be used in harsh working environments where gloved operation is required.

Explaining the basic operation is simple. First, the main screen operation parameter is selected and made the current function by pressing the appropriate function label (for example, Freq, Lev, AM1, IQ, W'form) on the touch-screen and the selected parameter is highlighted, as shown in Figure 1 . Once a parameter has been selected, its value can be changed in a conventional manner using the numeric keypad, increment/decrement keys or rotary control.

The 3410 series offers more than 30 different modulation combinations. Selection and control of any summarized modulation is made using the touch-screen. Pressing the required modulation summary box causes the display area to be reconfigured and the selected modulation settings displayed. The modulation parameters can then be adjusted by touching the appropriate function label.

Function sub-menus contain advanced features and additional controls for the main signal generator screen parameter selected. The available sub-menus are indicated at the bottom of the display as a series of touch "tabs'' and can be selected in turn by pressing the touch-screen. The use of "tabs'' creates a two-tier, flat menu structure, which means the operator can quickly switch from one to the other without having to scroll down and back up again. Therefore, the user is only one key press away from the main signal generator screen, where what is visible on the screen is what is being generated.

The ARB Feature

As mentioned earlier, the 3410 series includes an optional dual-channel arbitrary waveform generator, incorporating an interpolation filter design that reduces the ARB configuration process to a simple file selection operation. The interpolation rate of the filter is automatically set in such a way that aliasing products of the wanted signal are shifted into the stop band range of the anti-aliasing (reconstruction) filter. As a result, incorrect instrument configuration is avoided and correct file generation is guaranteed. Software control means that the user does not have to bother with setting it up as this is done by the software and hardware.

Files loaded into the ARB can have sample rates ranging from 17 kHz to 66 MHz. In addition, the interpolation hardware takes care of the (sin x)/x distortion that is a direct consequence of the sampling process and allows files to be created that have low nominal sample rates, resulting in smaller file sizes.

The ARB can store a maximum of 22.5 M samples in its non-volatile flash memory. This is partitioned into 60 sectors, each of which can be further divided into three sub-sectors, providing 180 sectors of file storage at any given time. Also, sectors and sub-sectors can be merged together to form larger files. The user can inspect the files stored in the ARB, as shown in Figure 2 . The list can be scrolled up and down and the required file selected.

Sweep Operation

A standard feature of signal generators is the provision of an automated method of changing parameters such as carrier frequency and RF. The 3410 series provides a simple method to provide this sweep configuration by using a novel method of user interface control. Sweep operation is set up and controlled by pressing a dedicated key, whereby globally recognized icons (see Figure 3 ) are displayed that mimic the controls seen on compact disk players and videocassette recorders. Pressing the appropriate touch-target allows the sweep to be started, paused and reset. When paused, additional controls are displayed that allow the sweep to be manually stepped backward and forward.

Parameter settings are accessed via the "Params'' tab. From here start, stop, step size and step time may be entered. Likewise, configuration settings are available from the "Control'' tab. The parameter to be swept can be defined (for example, carrier frequency) and the trigger operation (single shot/continuous) specified.

Conclusion

The 3410 series is a family of modular and upgradeable RF signal generators that is compact and portable and combines full digital, vector and analog modulation in one streamlined unit. Designed for R&D and manufacturing test applications it incorporates an entirely new interface that makes complex test scenarios easy to configure. In operation it exhibits the benefits that would be afforded by soft keys and a large screen but through the combination of a touch panel display and a keyboard alternative.

IFR Systems Inc.,
Wichita, KS (316) 522-4981 or (800) 835-2352.

Circle No. 301

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