HP 54121T 20 GHz Digitizing Oscilloscope (Pre-Owned)

Key Features At A Glance

• Bandwidth from 12.4 GHz (54122T) to 34 GHz (54123T) across the 54120-series digitizing oscilloscopes
• Four input channels with digital feedback sampling for repeatable, operator-independent measurement results
• 10 ps time interval accuracy and 0.25 ps time interval resolution
• Built-in time and voltage histograms for noise and jitter characterization
• Time Domain Reflectometry (TDR) with step generator on the 54121T and 54123T for transmission line analysis
• Fully HP-IB programmable with pushbutton hardcopy documentation to HP PaintJet printer
• 2.5 GHz edge trigger with external trigger input (40 mV peak-to-peak sensitivity dc to 100 MHz)
• Automatic pulse parameter measurements with 0.4% vertical accuracy

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.

Model	Bandwidth	Risetime	Channels
54121T	dc to 20 GHz	17.5 ps (Chs 2,3,4); 19.4 ps (Ch 1)	4
54122T	dc to 12.4 GHz	28.2 ps	4
54123T	dc to 34 GHz	10.3 ps (Chs 2,3,4); 17.5 ps (Ch 1)	4
54120B	—	—	—

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

Specification	HP 54121T
High Bandwidth (-3 dB)	dc to 20 GHz chs 2,3,4 (ch 1 is -3.5 dB @ 20 GHz); dc to 18 GHz, ch 1
Low Bandwidth	dc to 12.4 GHz
Transition Time, High Bandwidth (10% to 90%)	<17.5 ps, Chs 2,3,4; <19.4 ps, Ch 1
Transition Time, Low Bandwidth	<28.2 ps
Noise (rms), High Bandwidth	<2 mV
Noise (rms), Low Bandwidth	<1 mV
Scale Factor, Minimum	1 mV/div
Scale Factor, Maximum	80 mV/div
Attenuation Factors	N/A
Programmable dc Offset	± 500 mV
Inputs Number	Four
Dynamic Range	± 320 mV relative to channel offset
Maximum Safe Input Voltage	± 2 V dc + peak ac (+16 dBm)
Nominal Impedance	50 Ω
Percent Reflection	<5% for 30 ps risetime
Connectors	3.5 mm (m)
TDR System Risetime	<45 ps
TDR Flatness	<+1% after 1 ns from edge; <+5%, -3% to 1 ns from edge
TDR Levels Low	0 V ± 2 mV
TDR Levels High	+200 mV ± 2 mV

Important: Maximum safe input voltage on the trigger input is ±2 V dc + ac peak (+16 dBm) at a nominal 50 Ω impedance.Important: The HP 54121T 20 GHz Digitizing Oscilloscope consists of two model numbers, the HP 54120B Digitizing Oscilloscope Mainframe and the HP 54121A Four Channel Test Set. The HP 54121T is the recommended ordering configuration.Important: The HP 54122T 12.4 GHz Digitizing Oscilloscope consists of two model numbers, the HP 54120B Digitizing Oscilloscope Mainframe and the HP 54122A Four Channel Test Set. The HP 54122T is the recommended ordering configuration.Important: The HP 54123T 34 GHz Digitizing Oscilloscope consists of two model numbers, the HP 54120B Digitizing Oscilloscope Mainframe and the HP 54123A Four Channel Test Set. The HP 54123T is the recommended ordering configuration.Important: Normalization information is a characteristic, not a specification. The information is presented here for comparison purposes only. Normalization characteristics are achieved only with the use of the normalization calibrations and firmware routines.Important: Specifications measured in the low bandwidth and average display modes.Important: The risetime of the generator is less than 35 ps, as calculated by (Tr system)^2 = (Tr generator)^2 + (Tr scope)^2.Important: When operated within +/- 5 C (+/- 9 F) of the temperature of the last front panel calibration.Important: The input samplers are biased differently for increased bandwidth in the high bandwidth mode.Important: When driven from a 0 Ohm source.Important: For the HP 54123T, the 3% changes to 5% and the 1.5% changes to 2%.Recommended pairing: the HP 54006A 6 GHz resistive divider probe kit (10:1, 500 Ω and 20:1, 1 kΩ probes) provides hand-held probing access to circuit nodes that do not have a 50 Ω connector, including circuits that are not nominally 50 Ω.

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.