What are the primary differences in input protection between the R3261A and R3261C?

The Advantest R3261C provides internal protection against DC voltages up to ±25 V, whereas the Advantest R3261A has a maximum DC input voltage rating of 0 VDC and requires external caution to prevent DC bias from damaging the input mixer.

What type of display do these spectrum analyzers use?

The Advantest R3261A features a green monochrome CRT display, while the Advantest R3261C is equipped with a 5.5-inch CRT display.

What is the frequency resolution of the internal counter on these models?

The Advantest R3261C features an internal frequency counter with a fixed 1 Hz resolution. The Advantest R3261A frequency counter has a selectable resolution ranging from 1 Hz to 1 kHz.

Advantest R3261 Series Spectrum Analyzers

2 models with full specifications from Advantest.

The Advantest R3261 series consists of high-performance synthesized RF spectrum analyzers designed for precise signal analysis. This series, which includes the R3261A and R3261C models, covers a broad frequency spectrum from 9 kHz to 2.6 GHz. Engineered for engineers requiring accurate RF measurements, these instruments offer a fine 1 Hz tuning resolution, integrated frequency counter capabilities, and standard GPIB connectivity for system integration. While they share core signal analysis capabilities, they differ in their physical footprint, DC voltage tolerance at the input, and specific attenuator configurations.

Frequency Range: 9 kHz to 2.6 GHz
Tuning Resolution: 1 Hz
Standard Interface: GPIB
Weight: 15 kg
Warm-up Time: 30 minutes

Models in this series

Model	Type	Dimensions (W×H×D)	Display	External Reference Input
R3261A	*misc	355 mm × 177 mm × 450 mm	CRT display (green monochrome)	10 MHz, -10 dBm to +5 dBm, 50 Ω
R3261C	*misc	300 mm x 177 mm x 460 mm	5.5-inch CRT	10 MHz

Shared Performance and Synthesis Capabilities

Both the Advantest R3261A and Advantest R3261C are built on a synthesized RF architecture that ensures high frequency stability. They feature a reference frequency aging rate of ±2 × 10^-6 per year and a temperature stability of ±5 × 10^-6 over their operating range of 0 to 50 °C.

For spectral purity, both models display a SSB phase noise of ≤ -105 dBc/Hz at a 20 kHz offset, with residual FM kept below 20 Hz p-p per 0.1 seconds. The span settings for both units range from a narrow 1 kHz up to the full 2.6 GHz, alongside a zero span mode for time-domain analysis.

Physical Differences and Input Safety

The models differ significantly in their input protection and physical chassis design.

Advantest R3261A: Features a wider chassis measuring 355 mm × 177 mm × 450 mm. The RF input is highly sensitive to DC, with a maximum allowable DC input voltage of 0 VDC. Its maximum safe RF input level is +25 dBm, which requires at least 10 dB of attenuation.
Advantest R3261C: Designed with a more compact width of 300 mm × 177 mm × 460 mm. It offers higher input protection, withstanding a maximum DC input voltage of ±25 V. It includes an integrated input attenuation range from 0 to 50 dB selectable in 10 dB steps, and a maximum safe RF input level of +25 dBm.

Frequently asked questions

What are the primary differences in input protection between the R3261A and R3261C?: The Advantest R3261C provides internal protection against DC voltages up to ±25 V, whereas the Advantest R3261A has a maximum DC input voltage rating of 0 VDC and requires external caution to prevent DC bias from damaging the input mixer.
What type of display do these spectrum analyzers use?: The Advantest R3261A features a green monochrome CRT display, while the Advantest R3261C is equipped with a 5.5-inch CRT display.
What is the frequency resolution of the internal counter on these models?: The Advantest R3261C features an internal frequency counter with a fixed 1 Hz resolution. The Advantest R3261A frequency counter has a selectable resolution ranging from 1 Hz to 1 kHz.