The HP 85645A is a tracking source covering 300 kHz to 26.5 GHz, designed as a general-purpose accessory for spectrum analyzers (referred to as the host instrument). Combined with a host spectrum analyzer, the tracking source enables measurement of the swept amplitude response of devices such as amplifiers and filters. Because the spectrum analyzer is a tuned receiver, these measurements deliver high dynamic range and speed and are not affected by spurious signals or harmonics. The HP 85645A allows the user to choose either AC or DC coupling and provides selectable RF output power.

Listed applications for the HP 85644A and HP 85645A tracking sources include swept amplitude response measurements of amplifiers and filters, amplitude response measurements of frequency translation devices such as mixers and of systems with delays such as satellite links (using offset tracking), swept third-order-intercept (TOI) measurements when two tracking sources are set to appropriate offset frequencies, and power sweep measurements for characterizing the saturation effects of devices under test. The tracking sources can also generate stand-alone, non-synthesized CW signals at fixed frequencies of the user's choosing with no connections to a host instrument required. Combined with a transducer, the tracking source can perform swept measurements of circuit immunity to electromagnetic interference (EMC).

Brand Heritage

Hewlett-Packard's test and measurement division was spun out as Agilent Technologies in 1999, and the electronic measurement portion of Agilent became Keysight Technologies in 2014. HP-branded instruments such as the HP 85644A and HP 85645A trace through this lineage; service, calibration, and documentation references that originated under HP are typically continued through the Keysight organization today.

Compare Other Models in This Series

The HP 85644A and HP 85645A are companion tracking sources sharing the same operating concept: pair the source with a host spectrum analyzer to perform swept amplitude response measurements of amplifiers, filters, and other components. Both models offer a configuration menu, accessible from the front panel or via HP-IB, that selects the compatible host instrument and matches the source's behavior to that host.

The two models differ in two principal dimensions: frequency coverage and coupling. The HP 85644A covers 300 kHz to 6.5 GHz and is AC coupled. The HP 85645A extends coverage to 26.5 GHz and allows the user to choose AC or DC coupling. Both share the same I/O architecture, the same offset tracking and power sweep features, and the same environmental and calibration specifications.

Each pre-owned HP 85644A or HP 85645A in our inventory is listed as a separate product page with its own condition assessment, accessory list, and pricing. The model best suited to a given application depends on the customer's frequency coverage requirement, coupling preference, and host instrument; the linked pages below allow direct comparison of the two models within the family.

The HP 85645A is the wider-coverage model in the family, reaching 26.5 GHz with selectable AC or DC coupling. Its maximum leveled power output reaches +10 dBm in band 1 (2.0 to 7.0 GHz), and its dynamic range with an HP 8566A/B host reaches 141 dB in band 0. The HP 85645A uses an SMA (f) front-panel RF output.

The HP 85644A's 6.5 GHz coverage is appropriate for applications confined to the lower microwave range; the HP 85645A's 26.5 GHz coverage adds bands 2, 3, and 4 (covering ranges that extend through 13.5 GHz, 20.0 GHz, and 26.5 GHz respectively, with maximum leveled output of +5 dBm, +5 dBm, and -2 dBm). The HP 85645A's selectable DC coupling is the option to specify when measurements must extend below the AC-coupled lower limit of 10 MHz down to 300 kHz.

Other differences follow from this: the HP 85644A has a 70 dB attenuator range with characteristic accuracy of 1.2 dB maximum; the HP 85645A has a 60 dB range with 1.9 dB maximum characteristic accuracy. The HP 85644A is rated at <150 VA / <80 W and 10 kg nominal weight; the HP 85645A is rated at <200 VA / <110 W and 12 kg nominal weight. See the comparison table below for the band-by-band specifications.

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

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.