Many thanks to SWLing Post contributor, Grayhat, who shares the following:
I stumbled upon a document I found in the “CIA reading room”:
In short, the document, titled “HF SPACED LOOP ANTENNA” and dating back to 1967, describes the design of a “direction finding” antenna used to find an HF transmitter. The document describes a number of setups tried during initial experimentation and then explains the reasons for the selection of what’s called a “Coaxial spaced loop in vertical opposition”, basically two vertical loops connected in anti-phase; the document describes in detail the loop and some circuitry used with it, but the most interesting section is the one which deals with radiation lobes. if you look at that you’ll suddenly realize using such a configuration, the resulting antenna acts as a huge dipole with extremely deep nulls !!
Fascinating! Thank you, Grayhat.
And, honestly, there’s enough material in that CIA document to please the most demanding of antenna nerds! Most impressive. I’m curious if anyone has ever built one of these. If so, please comment with your experience!
(Source: The Intercept via Dan Robinson)
A SHORT DRIVE south of Alice Springs, the second largest population center in Australia’s Northern Territory, there is a high-security compound, code-named “RAINFALL.” The remote base, in the heart of the country’s barren outback, is one of the most important covert surveillance sites in the eastern hemisphere.
Hundreds of Australian and American employees come and go every day from Joint Defence Facility Pine Gap, as the base is formally known. The official “cover story,” as outlined in a secret U.S. intelligence document, is to “support the national security of both the U.S. and Australia. The [facility] contributes to verifying arms control and disarmament agreements and monitoring military developments.” But, at best, that is an economical version of the truth. Pine Gap has a far broader mission — and more powerful capabilities — than the Australian or American governments have ever publicly acknowledged.
An investigation, published Saturday by the Australian Broadcasting Corporation in collaboration with The Intercept, punctures the wall of secrecy surrounding Pine Gap, revealing for the first time a wide range of details about its function. The base is an important ground station from which U.S. spy satellites are controlled and communications are monitored across several continents, according to classified documents obtained by The Intercept from the National Security Agency whistleblower Edward Snowden.[…]
Continue reading at The Intercept…