TG Control V3

Tracking Generator for the HP 8562A/B Spectrum Analyzer

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

PA3AEF 2026

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.

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.

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:

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.

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.

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.

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

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

Status (Oct 19, 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: finshed (I have some boards available)
• Firmware: finished (Base-band, 6cm and 3cm)
• 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

License

MIT License.
See LICENSE for details.