How embassy eavesdropping works

Inside the interception galleries at GCHQ’s former Irish monitoring tower. The brown area of the wall is made from a special dielectric (insulating) panel – allowing radio waves to pass through and be intercepted, while blocking visible light and concealing the interception antennae behind (since removed).   Inset: Duncan shows where the antennae were sited.

The key visible feature of most embassy and diplomatic sites that give away their secret spying missions are large windowless areas on top floors, and also sheds or hangers on the roof which are designed to look as though they might contain lift or air conditioning apparatus. 

At the US Embassy in Berlin, the lighter coloured panels on the south west, north west and northeast corners of the rooftop surveillance facility are dielectric "radio windows" which allow all types of radio signals to reach collection and analysis equipment on the roof and floor directly below.

The "radio window" panels are made of special material which does not conduct electricity.   That is so weak radio signals coming in from all corners of the city are not diminished (attenuated) as they pass into the building and reach the sigint (signals intelligence) antennae.

Usually, dielectric window panels for signals intelligence work are made of plastic or fibreglass.   They are often shaped and coloured to look as though they are a normal part of the building, or are special architectural features.   

External Close up of Radio window panel at Capenhuirst

External Close up of Radio window panel at Capenhurst


Hidden behind the panels are a range of special monitoring antenna, dishes or arrays which collect every type of commercial and civil mobile, and government communications, including internet traffic, on all available wavelengths.

Rooftop "sheds" like in Berlin can be seen on dozens of US embassies in Europe and around the world, except in "Five Eyes" allied countries such as the UK.  Apart from the "collection" sheds, large processing areas are needed to analyse and transmit the result of interception to the global surveillance network. 

Windowless top floors, such on the south wing of the Berlin embassy provide "SCIFs" - Secure Compartmented Intelligence Facilities - which are needed to prevent any radio signals from the interception and analysis equipment themselves leaking out.    The processing operators and equipment for the "Special Collection Service" are sited in these rooms.

The largest and most obvious US diplomatic surveillance facility in Europe is on the roof of the Geneva consulate, overlooking the United Nations.    The Berlin eavesdropping facility is one of the largest, comparable in size to those in sensitive Middle East locations such as Yemen or Cyprus. 

When the former GCHQ surveillance installation in Capenhurst in northern England was retired from service and put up for sale (TV link), it was possible to inspect inside and see what the embassy surveillance centre might look like.

The 150 ft (50 metre) tower had been placed directly between two British Telecom microwave radio towers carrying telephone traffic. It was the ideal place to discreetly intercept international telephone calls of the Irish government, businessmen and also those of suspected of involvement with IRA terrorism.

The hi-tech tower included eight floors of advanced electronic equipment and three floors of aerial galleries.  These were used to extract and sort the thousands of communications passing through every hour.





 Channel Four: Capenhurst Tower

Channel Four news report on the mysterious Capenhurst Tower.

Reported and directed by Judy Aslett. See Streamline Productions


Other Links    

The Capenhurst Tower

In 1999, Richard Lamont published a piece about the Capenhurst Tower's interception capabilities.  After Duncan got in touch saying he wasn't convinced,the two set out digging together to definitively prove the tower's secret purpose. Read more

Bugging ring around Ireland

British electronic spies have been illegally bugging all telephone, fax, e-mail and data communications to and from the Republic since at least 1990 - and still are.

25 July 1999

Read more

How Britain eavesdropped on Dublin

Britain directed a massive bugging operation against the Irish government for 10 years — something that had been kept secret until now.

16 July 1999

Read more

Capenhurst press release

Official 1989 MoD press release announcing the construction of Capenhurst Tower.

Read more

Liberty v UK

Read the judgement of Liberty v UK

The embassy spy centre network

See images of US embassies and consulates from around the world and their spying operations.

Read more