Tracking Generator for the HP 8562A/B Spectrum Analyzer

Reconstructing the Analyzer’s RF Sweep from Its Local Oscillator A modular, analyzer‑synchronous architecture

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What this project is

The HP 8562A/B spectrum analyzer does not include a tracking generator.
However, it exposes enough of its internal LO system to build one externally.

This project implements a modular, sweep‑synchronous Tracking Generator (TG) that behaves as if it were a native part of the HP 8562A/B.
It reconstructs the analyzer’s RF sweep using only:

• 1st LO Output (about 3.9–6.8 GHz)
• LO Sweep Output (0–10 V, 0.5 V/GHz)
• 10 MHz reference

The TG becomes a slave to the analyzer’s LO system and rebuilds the RF sweep in real time across multiple microwave bands.

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Why build a Tracking Generator for the HP 8562A/B?

The HP 8562A/B is a legendary instrument: fast, sensitive, and extremely stable.
But without a tracking generator, it cannot perform:

• filter alignment
• cavity tuning
• antenna measurements
• scalar network analysis
• frequency response characterization

This project fills that gap with a TG that follows the analyzer sweep exactly, using the analyzer’s own LO architecture.

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How the analyzer sweeps — and how the TG reconstructs the RF

The HP 8562A/B does not sweep an RF source.
It sweeps its first local oscillator and mixes incoming signals down to a fixed IF.
To cover 1 kHz–26 GHz, it uses automatic harmonic mixing, where each RF band uses a different harmonic of the LO:

RF Band	Harmonic n	IF	LO Formula
1 kHz–2.9 GHz	1	3.9107 GHz	LO_SA = RF_SA + 3.9107 GHz
2.75–6.46 GHz	1	310.7 MHz	LO_SA = RF_SA + 0.3107 GHz
5.86–13.0 GHz	2	310.7 MHz	LO_SA = (RF_SA + 0.3107 GHz) / 2
12.4–19.7 GHz	3	310.7 MHz	LO_SA = (RF_SA + 0.3107 GHz) / 3
19.1–26.0 GHz	4	310.7 MHz	LO_SA = (RF_SA + 0.3107 GHz) / 4

For each band, the analyzer follows: n * LO_SA = RF_SA + IF

Because n changes with band, the analyzer LO becomes non‑linear with respect to the displayed frequency.

A tracking generator must compensate for this non‑linearity to stay aligned.

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How the TG reconstructs the analyzer RF

The TG uses the analyzer LO_SA (or a harmonic of it) as the primary LO and subtracts a fixed IF to recreate the analyzer’s RF:

RF_TG = (n * LO_SA) – IF_TG

Where:

• IF_TG = 310.7 MHz (fixed for all microwave TG modules)
• n = analyzer harmonic mode for that band

This yields:

• Base‑Band (n = 1):
  RF_TG = LO_SA – 3.9107 GHz

• 6 cm (n = 1):
  RF_TG = LO_SA – 0.3107 GHz

• 3 cm (n = 2):
  RF_TG = (2 × LO_SA) – 0.3107 GHz

• 12 mm (n = 4, concept):
  RF_TG = (4 × LO_SA) – 0.3107 GHz

This architecture reqires no swept PLLs in the microwave TG modules.
Sweep coherence comes entirely from the analyzer LO.

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High‑level TG architecture

The TG system is composed of modular RF boards:

• MCU board:
  Reads sweep voltage, computes RF_SA for calibration, programs PLLs

• RF SA‑LO Distribution board:
  Conditions and splits the analyzer’s 1st LO to all TG modules

• Base‑Band TG module:
  0–2.9 GHz (uses MAX2870)

• 6 cm TG module:
  4.4–6.4 GHz (LO_SA direct, IF_TG = 310.7 MHz)

• 3 cm TG module:
  9.5–11.5 GHz (LO_SA ×2, IF_TG = 310.7 MHz)

• 12 mm TG module (concept):
  22–26 GHz (LO_SA ×4, IF_TG = 310.7 MHz)

Conceptually:

Analyzer → LO Distribution → TG Modules → RF Outputs
Analyzer → 10 MHz → PLLs
Analyzer → V_sweep → MCU → Harmonic modules

Each TG module reconstructs the analyzer RF at its own band using a mixer‑based architecture.

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TG coverage limits

• Implemented TG bands:

  • Base‑Band (0–2.9 GHz)
  • 6 cm (4.4–6.4 GHz)
  • 3 cm (9.5–11.5 GHz)

• Conceptual / future TG bands:

  • 12 mm (22–26 GHz)

• Analyzer coverage:

  • Up to 26 GHz with Option 026
  • TG coverage currently ends at 11.5 GHz

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Repository structure

/docs/architecture
    01-tg-system-architecture.md
    02-lo-architecture.md
    03-analyser-lo-internals.md
    04-rf-sa-lo-distribution.md
    05-baseband-module.md
    06-6cm-module.md
    07-3cm-module.md
    08-12mm-module.md
/docs/architecture/images
    architecture diagrams
/firmware
    MCU firmware (Raspberry Pi Pico)
    overview
    images
/hardware/<module>
    schematics, layouts, BOMs, images
/mechanical
    enclosures, front panels
/usage
    calibration and measurement tools

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Status (Sep 27, 2026)

Checkout the discussion section for updates on the first results I have.

• File: example S21 3 cm lossy filter
• File: example S11 3 cm pole filter
• MCU board:
  • concept tested OK, new PCB in development to accomodate new 10 MHz distribution architecture
  • firmware tested OK. Waiting for final PCB to start polish and publish
• LO Distribution: finished
• Base‑Band module: finished
• 3 cm module: proof of concept tested OK (tracking at 10 GHz with 2 GHz span)
• 6 cm module: architecture defined
• 12 mm module: conceptual design complete

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License

MIT License.
See LICENSE for details.