The RACAL RA-17 and RA-117 were notable as the first production communications receivers to implement the Wadley Loop tuning system. The Wadley Loop was a technique to improve tuning precision and stability at higher frequencies in the days before phase-locked-loop systems were feasible economically. These were premium receivers in their day, and the choice of many Naval and commercial services in the 1950s and 60s.

Using these receivers is a unique experience relative to that of their contemporaries. The tuning precision and stability is remarkable for a tube receiver. The tuning dial is graduated with 1 KHz markings and the tracking can be accurate down to ± 1 KHz. The Collins R-390 is the only other receiver from the period with comparable tuning capabilities that I am aware of. The R-390 took a very different approach to achieving those abilities, employing multiple crystals and complex mechanical linkages. In contrast, the RA-17 and 117, using the Wadley Loop, rely on a single 1MHz crystal reference.

The Wadley loop was named for its inventor, Trevor Lloyd Wadley, a South African engineer also known for inventing the tellurometer, a microwave distance measuring device used in surveying. Both the Wadley Loop and the Tellurometer were based on sophisticated use of frequency-domain concepts.

In the 1970s, several solid-state receivers would be produced using the Wadley Loop, such as the Barlow-Wadley XCR-30, Yaesu FRG-7 and the Realistic DX-300. The technique was later made obsolete by the availability of digital synthesised tuning / PLL technology.

The SPARC Radio Museum originally obtained two RA-117s around the late 1990's as part of two racks of RACAL radio equipment that were removed from a decommisioned Canadian destroyer before it was sunk to become an artificial reef. In 2007 a further group of three (!) were donated to the museum. None of the five were functional as received. The first two from the destroyer were substantially intact and unaltered, while all of the group of three were a little beat up and had been hacked over internally: capacitors had been snipped out, some component boards were broken or removed, other bits and pieces missing. In 2008 we set out to get (at least) some of them working, starting with an assessment of the 5 units. In 2009 SPARC received an RA-17.

Visit the sub-pages linked below for more commentary on the RA-17 and RA-117. The schematic for the RA-117 presented here is a re-organised drawing based on a scan of the manufacturer's schematic.

Sub-pages: Technical Description Versions Rebuilding Alignment

RA-117 Schematic (sub-pages): 1 - Notes, Layout, Tube List 2 - Block Diagram 3 - RF Input, 1st VFO, Harm. Gen. 4 - 2nd VFO, Mixers, IF Filters 5 - IF Amp, Detector, Audio, AVC 6 - Power Supply

Unit Information: Initial Assessment Unit N0115 Log Unit N0144 Log Unit N0714 Log

Pop Culture Trivia: In the 1964 James Bond film "Goldfinger", several RA-17s can be seen in the background as electronic filler in the 'laser table' scene.

External Links, Other Sources

• Gerry O'Hara's page on the restoration of Unit N16 at the SPARC web site.
• IJL'S (OH5HOI) TECHNICAL PAGE'S with RA-117 manual.
• Keiths Vintage RACAL Enthusiasts Site.
• Ozemail RA-17 site.
• The RACAL shack of Henk, PA8PDP.
• Site about Trevor Lloyd Wadley. See gallery for photo of RA17s being assembled.
• Francesco Caizzi's site about the Barlow-Wadley XCR-30. See the "BW Story" for some mention of the early development of Wadley Loop receivers.