Thank you to Gean Stumbaugh (Worldwide Support Manager for High Frequency Measurements) and Christopher Rich (FieldFox Manager) from Keysight Technologies for the permanent loan of a Keysight FieldFox N9918A to the MIT Radio Society W1MX! This remarkable instrument combines a vector network analyzer (VNA), spectrum analyzer (SA), real-time spectrum analyzer (RTSA), and an RF power meter into a single ruggedized handheld instrument.

History of HP/Agilent/Keysight Instruments at Radio Society

The MIT Radio Society W1MX shared workshop has a long history of using HP/Agilent/Keysight instruments, and the club has many members who collect and repair older HP electronic test equipment. Among other instruments, we currently have:

• An HP 8551, which is the first microwave spectrum analyzer ever sold by HP in the 1960s – donated by the family of Steve Finberg (W1GSL) after his passing. This remarkable instrument was a harmonic spectrum analyzer with frequency range into the 10s of GHz with external mixing.
• An HP 141T spectrum analyzer – collected from a lab cleanout – the second harmonic spectrum analyzer sold by HP, extremely popular through the 1980s and the instrument many RF engineers today learned on
• An HP 8563e, a more modern HP spectrum analyzer from the 1990s with 26.5 GHz range – collected from an MIT lab cleanout by Tanner Packham (KM6JEY) and repaired by Daniel Desantis (KC3FKR) and Oliver Trevor (KM6WOX), on loan to the club from Tanner
• A Keysight 1 GHz digital oscilloscope and logic analyzer – donated by Keysight Technologies
• An HP 8656B 990 MHz RF signal generator – collected from a lab cleanout
• An HP 437B RF power meter – bought at the NEAR-Fest amateur radio flea market by Oliver Trevor (KM6WOX), on loan to the club
• An HP 8643a synthesized signal generator – donated by a lab, partially repaired (currently working on issues with modulation)
• Many lab power supplies

Applications in Amateur Radio

Although the FieldFox’s target markets typically include commercial, broadcast, and cellular applications, it’s extremely useful for amateur radio as well and will make a huge difference to the club’s ability to teach people how to design and build RF systems.

Some common amateur radio tasks that the FieldFox makes easier:

• Tuning cavity filters – amateur radio repeaters and some receivers typically involve resonant cavity filters, which allow us to achieve very high selectivity with minimal passband loss. Since amateur radio typically uses repurposed tunable commercial cavity filters operating outside of their intended range, we usually tune them manually. We previously did this on a HP VNA on loan to the club, but that was only capable of 1.3 GHz. The FieldFox’s fast update rate and high dynamic range allow us to manually tune cavity filters up to 26.5 GHz quickly and easily.
• Foxhunting – an amateur radio activity involving searching for a hidden transmitter – the FieldFox’s integrated GPS and RF power meter make it a powerful tool for foxhunting with greater accuracy than ordinary receivers
• Locating interference sources
• Designing and tuning antennas – having a highly portable VNA makes designing and tuning antennas in-situ much easier – most large amateur radio antennas have to be raised into the air for final tuning (since being near the ground affects them slightly), which often means that adjustments happen outdoors or on a roof
• Analyzing transmitter quality – the real-time spectrum analyzer capabilities of the FieldFox make it very good for checking a transmitted signal for harmonics and distortion – the FieldFox has the ability to measure Total Harmonic Distortion (THD) and modulation depth directly

Educational Applications

The FieldFox’s ruggedness, wide set of capabilities, and modern interface make it great for teaching. Many club members use the workshop for class projects involving RF (see projects page).