The HP 54121T is a 20 GHz digitizing oscilloscope built around the HP 54120B mainframe paired with the HP 54121A Four Channel Test Set. As part of the broader HP 54120-series, it combines high bandwidth, time domain reflectometry, four input channels, and superb stability in a fully programmable oscilloscope that needs no manual loop gain adjustment. Digital feedback sampling delivers repeatable, accurate, and operator-independent measurement results across the full input dynamic range.

The 54120-series is designed for high-speed device and circuit characterization, high-speed telecom analysis, and microwave design. Picosecond-level time interval resolution and accuracy support digital pulse parameter measurements in semiconductors and computers, while built-in time and voltage histograms characterize the noise and jitter encountered in telecommunications applications such as eye pattern analysis. On the 54121T and 54123T, time domain reflectometry locates and removes discontinuities in transmission line systems by identifying ringing and waveform distortion.

Brand Heritage

Hewlett-Packard's test and measurement business was spun out as Agilent Technologies in 1999, then transferred to Keysight Technologies in 2014. Instruments originally branded HP, including the 54120-series digitizing oscilloscopes, trace their corporate lineage through this chain.

Compare Other Models in This Series

The HP 54120-series digitizing oscilloscopes share the HP 54120B color mainframe and differ primarily in the bandwidth and risetime delivered by the paired four-channel test set. All three configurations — 54121T, 54122T, and 54123T — provide four input channels, digital feedback sampling, 0.25 ps time interval resolution, 10 ps time interval accuracy, and full HP-IB programmability.

The series spans dc to 12.4 GHz (54122T), dc to 20 GHz (54121T), and dc to 34 GHz (54123T) in high bandwidth mode. The 54121T and 54123T also include a switchable step generator and trigger input on their respective four-channel test sets, supporting time domain reflectometry. The 54122T four-channel test set substitutes internal attenuators (×1, ×3, ×10, ×30) for the step generator and extends the maximum scale factor to 2.4 V/div.

Each model below links to its own product page with pre-owned-matched pricing. Configuration, calibration scope, and accessory inclusions vary by model and condition, so the per-model page is the authoritative reference for what is actually in stock and what is included.

Within the family, the 54121T occupies the middle bandwidth tier at dc to 20 GHz, with 17.5 ps transition time on channels 2, 3, and 4 (19.4 ps on channel 1). It retains the step generator and trigger input found on the 54123T configuration but at the 20 GHz tier rather than the 34 GHz tier of the 54123T.

The three configurations differ on three primary axes. Bandwidth: 12.4 GHz, 20 GHz, or 34 GHz at the high bandwidth setting. Vertical scale factor maximum: 80 mV/div on the 54121T and 54123T versus 2.4 V/div on the 54122T (which includes internal ×1/×3/×10/×30 attenuators in place of the step generator). TDR capability: present on the 54121T and 54123T via the integrated step generator; not present on the 54122T.

Maximum safe input voltage also tracks the test-set configuration: ±2 V dc + ac peak (+16 dBm) on the 54121T and 54123T versus ±5 V dc + peak (+24 dBm) on the 54122T. All three share the same 50 Ω nominal input impedance, ±320 mV dynamic range (relative to channel offset on 54121T/54123T, multiplied by the attenuation factor on the 54122T), and 3.5 mm (m) input connectors. The comparison table that follows summarizes these differences across the family.

Additional differences in specifications beyond the few shown above are not listed here — see each model's full specifications below.

Accessories Supplied

• Operating and programming manuals for the HP 54121T
• Service manual for the HP 54121A
• Four input channels, switchable step generator, and a trigger input
• Five adapters, APC-3.5 (f-f) (HP P/N 5061-5311)
• Five coaxial shorts, SMA (m) (HP P/N 0960-0055)
• One anti-static mat with wrist strap (HP 9300-1484)
• RF accessories (HP P/N 54121-68701): Five 20 dB attenuators, APC-3.5 (f-m) (HP 33340C opt 020)
• Three 50 Ohm cables, SMA (m-m) (HP P/N 8120-4948)
• Two SMA (m) to BNC (f) adapters (HP P/N 1250-1200)
• One 50 Ohm termination, SMA (m) (HP P/N 1250-2153)
• One 50 Ohm termination, SMA (f) (HP P/N 1250-2151)
• One coaxial short, SMA (f) (HP P/N 1250-2152)
• HP 54121T Front Panel Reference Manual (HP P/N 54121-90903)
• HP 54121T Programming Manual (HP P/N 54121-90904)
• HP 54120 Family Getting Started Guide (HP P/N 5952-4239)
• HP 54120B Mainframe Service Manual (HP P/N 54120-90907)
• HP 54121A Service Manual (HP P/N 54121-90902)

Product Core & Specifications

About this used unit

• Warranty included
• Functional verification included
• Standard Calibration Upgrade Options: No Calibration Required, NIST Traceable, Z540.1 or ISO 17025 with Data, Z540.3 Guardbanding with Data.
• Note that unnecessary accessories may not be included (contact Test Architect to confirm).

Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.