[time-nuts] Measuring receiver...
djl at montana.com
Tue Jun 21 23:27:38 EDT 2016
Yes, very simple for people, very difficult for “machinery”.
> On Jun 21, 2016, at 7:01 PM, William H. Fite <omniryx at gmail.com> wrote:
> In the days of my misspent youth, I worked as a telegrapher (one of the
> very last) for a Norwegian shipping line. We sent and received both
> Norwegian and English though few of us were bilingual. Between ships and
> shore stations, there were about forty of us and we all could recognize
> each other's "fists" with near-perfect accuracy. This is not difficult,
> gentlemen, and does not require any esoteric signal analysis. Transmitters
> would be a different story.
> Bill KJ4SLP
> On Tuesday, June 21, 2016, John Ackermann N8UR <jra at febo.com <mailto:jra at febo.com>> wrote:
>> I've seen references that at least by the latter part of WW2 oscillographs
>> were being used to identify transmitters and/or ops. It should be possible
>> to deduce chirp, rise time, fall time of signals, all of which characterize
>> the transmitter, as well as element spacing and other characteristics that
>> help identify the operator, from oscilloscope snapshots of the demodulated
>> audio at various sweep speeds.
>>> On Jun 21, 2016, at 7:02 PM, Alan Melia <alan.melia at btinternet.com
>>> TX "fingerprinting" in WWII
>>> You seem to be forgetting that there were very few of the sophisticated
>> digital timing systems were available 75 years ago. Traffic analysis was
>> started early in 1938 or even before. By 1939 we knew all the nets used in
>> Europe and had "Y" ( a corruption of WI, Wireless Intercept )operators
>> monitoring the nets. Many of these were amateurs and they were allocated to
>> specific nets and followed them around as they moved. They became very
>> familiar with the "accents" of operators on their nets, and particularly
>> before 1939 security procedures were very lax and "chatting"
>> common-place.....but it was all aural.
>>> I suspect serious transmitter parameter logging was not done before the
>> cold war when spectrum analysers, or at least pan-adapters became more
>> readily available. To keep a little OnTopic .....you would have difficulty
>> doing this with a BC-221.!! :-)) A crystal clock of this period was at
>> least one fully utilised 6foot 19inch rack (there is one at Grenwich.)
>>> ----- Original Message ----- From: "jimlux" <jimlux at earthlink.net
>>> Sent: Tuesday, June 21, 2016 10:02 PM
>>> Subject: Re: [time-nuts] Measuring receiver...
>>>>> On 6/21/16 11:28 AM, Brooke Clarke wrote:
>>>>> During W.W.II there were secret methods of "fingerprinting" radio
>>>>> transmitters and separately the operators.
>>>>> I suspect the transmitter fingerprinting involved things like frequency
>>>>> accuracy, stability, CW rise and decay time, &Etc. For the operator
>>>>> from of statistics on the timings associated with sending Morse Code.
>>>>> But. . . I haven't seen any papers describing this. Can anyone point
>>>>> me to a paper on this?
>>>> For "human controlled" stuff, e.g. recognizing someone's "fist",
>> there's a huge literature out there on biometric identification looking at
>> things like keyboard and mouse click timing - the timing requirements are
>> pretty slack, and hardly time-nuts level, unless you're looking to do it
>> with mechanical devices constructed from spare twigs and strands of kelp.
>>>> There have been a variety of schemes for recognizing individual radios
>> by looking at the frequency vs time as they start up. Likewise, it's pretty
>> easy to distinguish radar magnetrons from each other. Not a lot of papers
>> about this, but you'll see it in advertising literature, or occasionally in
>> conference pubs (although I can't think of any off hand). There was
>> someone selling a repeater access control system that was based on the
>> transmitter fingerprint.
>>>> But the real reason why you don't see any publications is that this
>> stuff is pretty classic signals intelligence (SIGINT or MASINT) and it is
>> still being used, and is all classified. You're not relying on Betty the
>> receiver operator to recognize the characteristic chirp as the agent's
>> radio is keyed, it's all done by computer now, but the basic idea is the
>> same. And as with most of this stuff, the basics are well known, but the
>> practical details are not, or, at least, are the proprietary secret sauce
>> in any practical system. (In a significant understatement, Dixon, in
>> "Spread Spectrum Systems" makes some comment about how synch acquisition is
>> the difficult part and won't be described in the book)
>>>> You might look at the unclassified proceedings of conferences like
>> MILCOM and find something. Googling with MASINT might also help.
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Felix qui potuit rerum cognoscere causas.
Lucky is he who has been able to understand the causes of things.
"Noli sinere nothos te opprimere"
Dr. Don Latham, AJ7LL
Six Mile Systems LLC, 17850 Six Mile Road
Huson, MT, 59846
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Frenchtown MT 59834-0404
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