The GPR40 range of interference measuring radio receivers were developed by a British company, Chase Electronics, based (when I joined them at least) in a two storey industrial building, St. Leonards House, close to Mortlake railway station in East Sheen, South London.
The GPR40 was a highly specialised device, each of which was hand built, with a list price of around £10,000 in 1986.
At some point the rights to the devices was sold to a German company, Willtek Communications GmbH.
I am aware of the following models, please use the contact page if you can add any more information to the list!
Presumably this existed as at least a prototype but it was before my time
GPR40.2 / Willtek 8100
This is the version that I worked on. At some point the rights appear to have been sold to Willtek GmbH of Ismaning, Germany.
Flyers and Manuals
Promotional material and basic user manuals can be found on this page.
Schematic diagrams of the electrical circuits can be found on a separate page.
A partial set of assembly diagrams showing the main physical sections of the reciever can be found here.
It is possible to control all the functions of the GPR 40 over an RS232 serial interface. Full details of this can be found here (this was my major contribution to the GPR reciever development).