The Latest Spectrum Analyzer Family from Aeroflex Sets New Standards in Performance, Features, and Cost
By David Asquith, Aeroflex Product Manager, Signal Sources and Spectrum Analyzers, Aeroflex

There are four models in the 3250 Series range of spectrum analyzers available in the frequency ranges from 9 KHz to 3 GHz, 8 GHz, 13.2 GHz and 26.5 GHz. The frequency range covers everything from radar and satellite, wireless and cellular, UHF, VHF and HF, right down to 9 KHz for EMC requirements. The digital IF processing stage provides resolution bandwidth digital filters from 5 MHz down to 1 Hz, providing a filter bandwidth to suit most measurement requirements.

With an SSB phase noise at 1 GHz of –115 dBc/Hz, 10 KHz offset, a low noise local oscillator provides the high performance required for testing of quality oscillators and transmitters. Such performance supports a phase noise measurement mode, which allows the user to plot the phase noise profile of an applied signal at offsets from 10 Hz to 1 GHz.

Dynamic range is an essential aspect of a spectrum analyzer’s ability to resolve low level signals as well as high level signals with a minimum of compression and distortion. At 1 GHz, a displayed average noise level (DANL) of –145 dBc/Hz and a third-order intercept (TOI) of +15 dBm provide the dynamic range to fully exploit the analysis of wide and narrow band analog and digital signals. Such performance adds to the applicability of the semi-automatic measurement modes such as adjacent channel power, channel power, occupied bandwidth, intermodulation, X-dB down, harmonic distortion, complementary cumulative distribution function (CCDF), and spectral emissions. These semi-automatic measurements help to ensure that user error is minimized. The maximum input signal rating is +30 dBm, which allows testing of low power transmitting systems by direct connection.

Vector Analysis
The “vector analyzer” mode enables a 14-bit digitizer with 30 MHz bandwidth. Signals may be displayed as FFT, polar, in-phase/quadrature (I/Q), power versus time, CCDF, or as a spectrogram. The spectrogram is a plot of frequency versus time, which can show, for example, the presence of short-duration spurious signals, or how the adjacent channel performance of an amplifier can change as its input level is varied. Modulation analysis of generic PSK and QAM signals provides measurement of error vector magnitude (EVM), RMS and peak, Rho and message error rate (MER). (Reference Figure 1) for the spectrogram function showing compression effects on a 3GPP signal as input level is increased.

Optional wireless analysis suites are available for WLAN, WiMAX, and uplink analysis for CDMA2000/1xEVDO, UMTS/HSUPA and GSM/EDGE. Measurements are presented in accordance with the relevant standard’s specification and where applicable, cover measurements such as ACLR, code domain power and error, magnitude and phase error, gain imbalance, I/Q skew, origin offset, and spectral flatness. The constellation and eye-diagram functions show pictorially how errors present in a system affect the EVM. The CCDF function provides an easy to understand graph of the statistical properties of a signal from which the crest factor is derived–an important measurement when testing amplifiers.

8 GHz Tracking Generator
Already available with a 3 GHz tracking generator option, the latest major new feature for the 3250 Series is a tracking generator covering the frequency range to 8 GHz. This broadens the instrument’s applications by enabling simple scalar analysis of components, filters, amplifiers, and sub-assemblies over the key wireless bands. It also extends capabilities into some microwave applications, covering the complete 4−8 GHz C−band used for ground-satellite communications, TV broadcast, military radar, and increasing use by state/government utilities. Normalization may be applied to remove the frequency response effects of interconnecting cables and connectors, the tracking generator output, and the spectrum analyzer input so that only the response of the DUT is analyzed. The high dynamic range of the spectrum analyzer receiver allows the user to see the skirt responses of filters even though they may be more than 80 dB below the pass band response. The sequence of pictures in Figure 2 shows how a 185 MHz low pass filter is characterized.

The output level of the 8 GHz tracking generator may be adjusted over a 20 dB range with a resolution of 0.5 dB. This provides additional flexibility when testing the frequency response and compression characteristics of amplifiers and other non-linear devices, by providing fine control at the point where compression starts to occur, for example.

Demodulation
Recently enhanced on the 3250 Series spectrum analyzer is the AM/FM Demod function. As with all demodulation functions, the spectrum analyzer is set to zero-span mode to fix the local oscillator such that the variations (modulation) of the input signal can be detected and analyzed. By selecting an appropriate resolution bandwidth (RBW) filter, it is now possible to demodulate AM and FM at modulation frequencies from 1 Hz to 30 KHz–the full audio band. The demodulated signal may be listened to by using the audio output via a front panel jack or internal speaker.

Also, in zero-span mode, it is possible to demodulate a pulse-modulated signal. Recent enhancements to the 3250 Series now make it possible to perform accurate sub-microsecond rise/fall time measurements using the comprehensive markers facility.

EMI Measurement
An EMI pre-compliance measurement option for the 3250 Series is an optimized solution for EMI pre-test and debugging in the development and manufacturing of electronic equipment conforming to international EMI standards. Main features include an internal preamp to 3 GHz, 6 dB EMI measurement bandwidth filters conforming to CISPR, CISPR detectors for Peak, Average, Quasi-Peak and RMS, and an optional preselector for the CISPR A and B bands (up to 30 MHz). An EMC configuration dialog box enables six ranges to be independently configured for start/stop frequency, step size, measurement time, RBW, preamp and attenuation. Correction factor tables for antenna, cable, and other gains/losses may also be configured and enabled accordingly. Reference Figure 3 for EMC configuration dialog.

The recent addition of an internal preselector option provides many benefits, especially when performing open-site measurements. The preselector is a narrow-band filter that removes large unwanted external signals at higher frequencies, which could otherwise overload the input and affect the dynamic range of the measurements being performed. This is especially critical when the built-in preamp is enabled. Toward DC, it removes spurious generated by, for example, pulse edges, allowing sensitive EMI measurements to be performed at low frequencies. Above 30 MHz, the EMI test can scan in by-pass mode.

General Features
The 3250 Series display consists of a 7-inch LCD touch screen display with 800 x 480 pixel resolution that provides comfortable viewing of the displayed data. While the front panel keyboard and rotary control offer conventional, easy operation, the touch screen and the ability to connect a mouse and keyboard via the USB interfaces offer a choice of GUI controls.

Four USB interfaces are provided – two on the front panel and two on the rear panel. Even when a mouse and keyboard are connected, there are still two USB ports available for memory storage (measurement data, screen dumps, limit files, configuration files, etc.). Picture formats can be BMP or JPG and tabular data can be stored as CSV files for later import into a spreadsheet such as MS Excel™. A USB interface may also be used for updating the instrument’s software. A removable 80 GB hard disk drive is fitted as standard for use in secure areas. This is the default location for the storage of all user settings and data.

For remote control, both RS232 and IEEE 488 (GPIB) are included and a LAN port with internal network server allows for monitoring, control, and remote calibration applications.

Weighing in at just 24 lbs., the 3250 Series is can be used in the field, on an R&D bench, or as a production test system. For field use, an external battery can be connected to an optional DC input.

AEROFLEX
www.aeroflex.com
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