[NJARC] Hedy Lamarr

[Harry Klancer]

Nick,

Frequency hopping is most certainly used and being further developed 
today - if
you hear about "spread spectrum", frequency hopping is one of the 
techniques used
to spread a transmitted signal across a wide band and to achieve the two 
things that
I mentioned, noise immunity and a certain amount of information security 
- and also to
increase the capacity of a frequency band. For example, the FCC has 
assigned
75 channels in the Industrial-Scientific-Medical (ISM) band around 2.4 
GHz. In theory,
each could be used for a single communication channel, but using 
low-power and frequency
hopping, any given receiver just sees the other signals as a slight 
increase in channel noise rather
than as a specific interfering signal (since the other signals hop 
around randomly). The result is
that you can get a lot more than 75 signals through.

Frequency hopping isn't used for cellphones (as far as I know) but it is 
used
for Bluetooth devices, and for some new work in so-called ultra-wideband 
communications.
I'm sure some folks on the reflector can tell you about some other uses. 
(Al, are there military
communication systems that use FH as part of their security?)

By the way, wireless local area networks - WiFi - use another technique 
called OFDM - orthogonal
frequency division multiplexing. OFDM also uses a lot of carriers, but 
they are sent simultaneously
rather than one at a time, and they are  spaced so that each carrier 
frequency is at the minimum
point of the adjacent carrier's (and the more distant carriers, also) 
spectrum.

Yes, Hedy is still with us.

                                                Harry K




NICHOLAS SENKER wrote:
> Visit our web site - See http://www.njarc.org
> _______________________________________________
> Thanks Harry, This is very interesting.  Is this technique still used, say for cell phones?
> Nick
>
> ----- Original Message -----
> From: Harry Klancer <klancer2 at comcast.net>
> To: New Jersey Antique Radio Club <njarc at mailman.qth.net>
> Sent: Wed, 2 Apr 2008 21:39:27 -0400 (EDT)
> Subject: Re: [NJARC] Hedy Lamarr
>
> Visit our web site - See http://www.njarc.org
> _______________________________________________
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>   
>> Visit our web site - See http://www.njarc.org
>> _______________________________________________
>> An article in yesterday's Newark Star Ledger about Hedy Lamarr (not to be confused with Hedley Lamar in 'Blazing Sadles') discribes the sultry beauty as not only a  great actress but also a 'brainy beauty'.  This is not an April Fool's joke!
>> To quote the article (p 29):
>> 'in the early 40's Lamarr came up with the concept of frequency hopping. Her invention was 40 years ahead of its time. It was a secret communication system.  It was the first time wireless radio transmissions could be sent and received without being intercepted.  Her children stress how the wireless world uses frequency hopping today with PDAs, wireless phones, and Wi-Fi. Composer George Antheil implemented Lamarr's concept.  He and the Vienna born actress received a patent which they gave to the US government.'
>> Amazing!
>> Can someone explain frequency hopping?
>> Nick Senker
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