A high‑stability 10 MHz OCXO replacement board for Racal Dana 19xx series frequency counters and timers.

Designed as a direct drop‑in upgrade for the original crystal and TCXO reference modules.
 
This module replaces the original Opt 04STD, Opt 04C and Opt 04T timebase options and provides significantly improved short‑term stability and long‑term ageing performance, verified through extended GPS‑referenced testing.
 
Compatible Racal Dana Models
Racal Dana 1991 Universal Counter
Racal Dana 1992 Universal Counter
Racal Dana 1998 Frequency Counter
Racal Dana 1999 Frequency Counter

Why Upgrade?
Many Racal Dana 19xx counters were originally fitted with basic crystal or TCXO reference boards, typically offering frequency accuracy in the 10⁻⁶ to 10⁻⁷ range. While adequate when new, these references often drift with age and are difficult to adjust reliably.
This OCXO upgrade provides more than two orders of magnitude improvement, achieving typical stability better than 1×10⁻⁸, with measured results frequently exceeding this figure in real installations.
 
Key Features
Drop‑in OCXO replacement PCB – no wiring or modification
Replaces Opt 04STD, Opt 04C and Opt 04T timebases
High‑stability 10 MHz OCXO reference
Rear‑panel accessible fine‑frequency adjustment
Uses original Racal 5‑pin board‑to‑board connector
Factory soak‑tested and GPS‑aligned prior to shipping
 
Performance (Typical)
Temperature stability (0 °C to 70 °C): better than 1×10⁻⁸
Ageing: typically ≤ 5×10⁻¹⁰ per day
Short‑term stability measured at sub‑ppb levels when installed and settled
 
Installation Summary
Installation is straightforward and typically takes around 10 minutes using a small Posi‑Drive / Phillips screwdriver. 
 
Unplug the counter from its supply
Remove the rear bezel (2 screws) noting which way up it was orientated as it only fits back on one way.
Slide off the case
The original reference PCB is mounted by a single screw and into a 5 pin header on the PCB. See photos. Remove the screw and the original PCB taking care not to lose the screw and washer.
Mount the new PCB into the counter as shown in the photos and secure with the screw. The rear mounted adjustment trimmer need to point towards the back panel
Take care to make sure you have aligned all the pins on the main board with the socket on the new oscillator PCB
Reassemble the case and rear bezel.
 
Testing & Calibration
Each OCXO PCB is:
Soak‑tested for 24 hours
Aligned against a GNSS‑disciplined 10 MHz reference
Verified prior to shipment
 
Warranty
All OCXO upgrade boards are supplied with a 12‑month warranty against failure.