Talk:Spread spectrum

Hedy Lamarr

Yes, Hedy (Not Headley) Lamarr the film star invented a rudimentary spread spectrum technology during world war II. Basically it was a a piano roll that controlled a radio tuner, forcing it to switch channels at regular intervals. Both sides of the conversation started the roll at the same time and then proceeded to talk normally. If you didn't have a copy of the roll, you would lose the conversation every couple of seconds and have to go find it again, which meant it was effectively impossible to eavesdrop. Here's a webpage about it: [1]. Here's some info about her patent: [http://inventors.about.com/library/inventors/bllamar.ht

Only she didn't. This is a meme (yes, a meme, not an inspirational poster some people confuse the two.) Spread spectrum was already well-established by 1941 - patents cite the technique as early as as 1903. George Antheil invented a technique to operate SS, but Lamarr was only one of many to suggest it. Did she have the idea? There's good evidence (albeit circumstantial) that she was simply parroting the idea from something she had overheard her first husband (a Nazi sympathise) say. Here's one example of an early spread spectrum technique. http://www.physics.princeton.edu/~trothman/Zenneck_secrecy.pdf Smidoid (talk) 18:49, 22 November 2013 (UTC)

Combining sections

The discussion in the history section seeems somewhat redundant with some of the "notes" in the next section.

Suggest we remove the redundancy, but didn't want to make so big a change without requesting views of others.

POV?

Note the following line: "(She learned about the problem after being forced to attend defence meetings with her ex-husband while she was in Germany prior to WWII)"

I can't see a source for this listed under the references in the article, so it seems to me like a simple and very out-of-place attempt to discredit Hedy Lamarr. So I removed it.

Reference added, line modified and added back in. Why that statement would discredit her is beyond me.

P.S. Please sign your posts. --QEDquid 17:44, 18 July 2006 (UTC)

The more I research this it appears that some of the claims (and probably the most crucial one) in re: of Spread Spectrum is invalid. Antheil and Lamarr invented a technique to employ spread spectrum, that is not in doubt, but I think that crediting them with the invention as many have, and many more ignore Antheil, is a folly. I'm no patent expert but if Tesla had been granted a patent in 1903 (not to mention the Germans using it on the battlefield in 1914-18) that sounds awfully like prior art. Prior Art (i.e. someone already did it) is any public domain document (in theory, anywhere) that describes the invention or claim. There's a suggestion - which I cannot verify right now - that Lamarr may even have had prior knowledge of Spread Spectrum via her military connections. I know this is deeply offensive to some - who hold Lamarr up as some example that a woman of such beauty can also be a genius - but we have to try and get to the facts; no matter how unpalatable they are. Here is some work with links to Tesla's patent for reference. 18:05, 21 November 2013 (UTC) smidoid —  Smidoid (talk) 17:30, 22 November 2013 (UTC)

References

SIGSALY

I am puzzled by the SIGSALY refernce in this article. When you read the SIGSALY article there is mention of a lot of pioneering innovations but none directly related to either frequency hopping or direct sequence. Suggest that someone either clarify the discussion of SIGSALY here and on its own article or else we remove this point.

On the other hand, I can see that SIGSALY may have been the first example of synchronizing pseudonoise generators at both ends of a communications link. (I suppose a pair of phonograph records with the same exact random noise would be in effect "pseudonoise" although others may disagree over the semantics.) Of course, spread spectrum today usually uses LFSR or cryptographically generated nonlinear PN - not one time pads on phonograph records.

SIGSALY is a frequency shifter - using a FM signals shifted by a noise pattern - based on one-time pads generated by efficient white noise at 50 samples per second. It's a technologically superior and crucially, earlier, invention. This is a case of prior art being missed, ignored or misunderstood by the patent examiners who granted Lamarr and Antheil the patent for their device. Antheil's method was certainly novel (and more arguably more robust for torpedoes) but never adopted. Smidoid (talk) 17:29, 22 November 2013 (UTC)

Modulation?

Is Spread Spectrum a modulation technique?

That point is not clear in the article. In related articles (see CDMA), is pointed out that spread spectrum techniques can be used, and are used, for multiplexing purposes. In CDMA article is established that it is NOT a modulation technique. On the other hand, in this article, it is mentioned that "Ultra Wideband (UWB) is another modulation technique", suggesting that spread sprectrum is, as well, a modulation technique. Is it? —The preceding unsigned comment was added by 158.227.115.40 (talk) 09:02, 21 February 2007 (UTC). Acprisip 09:12, 21 February 2007 (UTC)

I would say yet, SS is a modulation technique.

In theory, the standard definition of "modulation" seems like it might exclude spread spectrum.

In practice, spread spectrum systems have a "modulator" (a frequency mixer) identical to AM radio systems. The only difference between an AM radio system and a spread spectrum system is that the AM radio system feeds a constant pure sinewave at a fixed frequency to the modulator; a FHSS system feeds a fairly pure sinewave (at a frequency that keeps jumping around) to the modulator; and a DSS system feeds a high-speed digital "chip sequence" to the modulator. All these systems feed the same baseband signal to the other side of the same modulator, and send the output of the modulator to the same amplifiers and then out to the antenna.

May I ask what difference it would make whether we consider SS a modulation technique or (as suggested in the modulation article) merely a line code ?

--75.37.227.177 05:13, 15 July 2007 (UTC)

Practical how-to article

The external link Experimental direct sequence spread spectrum voice link was deleted. Please re-instate it. --80.177.105.226 13:10, 13 April 2007 (UTC)

Spread Spectrum Clock

Searches on "Spread Spectrum Clock" and "Spread Spectrum Clocking" suggest this page as a related result, but neither redirect here. Recommend linking these searches to this article since these terms are defined and discussed in the related section. —Preceding unsigned comment added by Mrbynum (talk • contribs) 17:30, 30 October 2009 (UTC)

•  Done. Now spread-spectrum clocking, spread-spectrum clocking, Spread Spectrum Clock, Spread Spectrum Clocking, spread spectrum clock, and spread spectrum clocking all redirect to the "Spread-spectrum clock signal generation" subsection of this article. --DavidCary (talk) 16:23, 9 May 2013 (UTC)

re: History - Frequency Hopping

The third paragraph in the History (Frequency Hopping) section contains the following sentence:"A Polish engineer, Leonard Danilewicz, came up with the idea in 1929."

This is incorrect, and/or poorly worded considering the first sentence of the section reads "The concept of frequency hopping was first alluded to in the 1903 U.S. Patent 723,188 and U.S. Patent 725,605 filed by Nikola Tesla in July 1900. "

68.61.181.176 (talk) 13:10, 9 November 2011 (UTC)

Jollydirtyoldwoman speaking: The assertion that MAGIEC participated in frequency hopping work needs citation. I worked there for a decade advocating frequency hopping while management disparaged it declaring it didn't work well. (They were a direct sequence house it appears.)

Rockwell International in Anaheim (formerly Autonetics) produced three different proof of concept frequency hopping radios while I was there, prior to my work at MAGIEC. One was completed just before I joined the company and the other two of which I directly participated in developing. (Anecdotally speaking I was astounded at how effective it was against then current jamming technologies.) /Jollydirtyoldwoman — Preceding unsigned comment added by Jollydirtyoldwoman (talk • contribs) 06:44, 2 February 2012 (UTC)

split

When I see lots of incoming links to some section of an article (whether direct links or indirect redirects), that usually means that sub-section is notable enough to promote to its own stand-alone article. Is it time to apply WP:SPLIT and WP:SUMMARY to the "Spread-spectrum clock signal generation" subsection of this article. ? --DavidCary (talk) 16:05, 9 May 2013 (UTC)

Proposed merge with Active EMI reduction

unsourced stub - better spun out Widefox; talk 18:08, 29 September 2015 (UTC)

Inconsistency with CSS article

In this article, we can read:

"Frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), time-hopping spread spectrum (THSS), chirp spread spectrum (CSS), and combinations of these techniques are forms of spread spectrum. Each of these techniques employs pseudorandom number sequences—created using pseudorandom number generators—to determine and control the spreading pattern of the signal across the allocated bandwidth."

In the CSS article, we can read:

"However, it is unlike direct-sequence spread spectrum (DSSS) or frequency-hopping spread spectrum (FHSS) in that it does not add any pseudo-random elements to the signal to help distinguish it from noise on the channel, instead relying on the linear nature of the chirp pulse."

I'm not an expert and not really sure about what's true, but I wanted to point out this contradiction. A source would be helpful. — Preceding unsigned comment added by 88.140.185.33 (talk) 22:33, 2 October 2017 (UTC)

Yes, you're right, chirping is not pseudorandom – though it could be, e.g. by time or frequency hopping the chirps randomly. Dicklyon (talk) 05:54, 14 January 2019 (UTC)

Spread spectrum vs frequency hopping

Spread spectrum is not quite the same as frequency hopping. It is a pretty well-known mix up that happen in the 80s if I remember correct, and comes from marketing of military equipment. Researchers know how to make real spread spectrum devices, and some marketing people abused the terminology to sell frequency hopping devices. You may say they are the same, because both tend to smear a signal out over a wider frequency range, but a frequency hopper (and also chirp) is really just avoiding manual retuning. In an automated scenario they are nothing more than plain ol' radio with changing frequency. Real spread spectrum smears the signal out in such a way that an automated radio can't follow the signal. An automated radio these days are a very fast spectrum analyzer that locks on the signal. Jeblad (talk) 23:00, 12 April 2020 (UTC)