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Radio Fingerprinting - RFP

According to Wikipedia: Radio fingerprinting is a process that identifies a cellular phone or any other radio transmitter by the unique "fingerprint" that characterizes its signal transmission. An electronic fingerprint makes it possible to identify a wireless device by its unique radio transmission characteristics.

175th RRC SIT NCS during Vietnam WarNCS of 175th RRC in Bien Hoa Vietnam. Left to right; Flash Op, DF Controller, RFP Op. RFP equipment is an upgraded Visicorder system. (Photo source: The Most Secret War, James L. Gilbert, Military History Office, USAINSCOM)

Extracted from received email, February 2011:

"jeez, we can do better than what's written--try this:
Radio Fingerprinting was the analysis of frequency & amplitude modulations to determine similarities and distinctions. The signals were captured with a hi-speed camera using = paper-based film and developed via a special processing machine. There were analysts specially trained to do the analysis. There was also a trick on being the operator as a primary goal was to capture a majority of "dahs" vice "dits". You also had to be aware of just when the tgt was about to stop transmitting or else you just might push the "record" button and waste 20 ft of film!" ~ Jim Sessoms

Three definitions from the NSA:

(U) Special Identification Technique(s) (SIT) - A collective term including Morse operator analysis, radio fingerprinting, and direction finding. GCHQ's term is Technical Aids..

(U) Advanced Identification Technique (AIT) - A technique of emitter identification involving analy of unintentional variations in amplitude modulation and frequency modulation which occur in target emissions. Preferred term for "radio fingerprinting", "waveform analysis."

(U) Radio Fingerprinting (RFP) - identify and classify the unique characteristics of individual radio transmitters by the study of oscillograms of their signals. Also called transmitter identification.

(Source: National Security Agency (NSA) FOIA release 7 June 2006 in letter to Mr. Steven Aftergood, Federation of American Scientists. Document is available on NSA web-site.)

Again from; The Most Secret War: (Regarding usage in Vietnam)

"While in Vietnam ASA found itself engaged in a number of minor projects that consumed a disproportionate amounts of its engeries. One of the diversions was radio fingerprinting (RFP). First used in World War II, radio fingerprinting involved the recording of characteristics (such as power and frequency variations) of an intercepted signal in order to identify a specific radio transmitter. An oscilloscope converted a signal into a visual format that could then be captured on film. To make this happen, the intercepted signals had to be of sufficient strength. Furthermore an experienced operator was needed to interpret the results. What many did not fully grasp was that radio fingerprinting was never meant to stand alone, but rather to be used in conjunction with other identification tools. RFP was far from an exacting methodology, and in Vietnam, it would face added challenges. (Source, page 49: The Most Secret War, James L. Gilbert, Military History Office, USAINSCOM) (Bolding and emphasis added)

Finally, from the same source as above, page 48:

"The fact that the RFP positions continued to operate at all was simply due to good coordination between personnel at the various stations. If somebody had something the other guy didn't have, he'd loan it to him or give it to him. This, of course, didn't always work because everybody ran out from time to time."