[NJARC] Hedy Lamarr (again)

[Harry Klancer]

Actually, it IS spread spectrum frequency hopping. A number of
subchannels are defined across a wide band, and then the specific
subchannel used for any short sequence of data bits to be sent is selected,
if I remember correctly, by ORing a Walsh code sequence with
a pseudorandom noise sequence. The transmitter and receiver
"know" what the Walsh code bit should be, and also know the
seed for the pseudorandom bit sequence. Therefore, the receiver
"knows" in which subchannel your data bits should appear. The next
subset of data bits will appear in a different subchannel based on
the Walsh code and pseudorandom bits expected at that time.

If you are some other receiver, and you do not know my
Walsh and pseudorandom code seed, you do not know in
which subchannels to look (kinda like 'whack a mole').
so all you receive is noise (probably white noise, but I'm
not sure about the statistics)

Anyway, that's how I remember it - might be wrong in
some particulars, but that's the basic story. Hence, the selected
subcarrier DOES hop across the wide band used for your
(and everybody else's) messages. But my bits are mine,
yours are yours, (and there's security and no interference).

It's just that Hedy used a player piano roll to select the
subcarrier rather than a pseudorandom sequence.

                                     Harry K


On 11/09/2015 5:21 PM, Bill Zukowski wrote:
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> _________________________________________________________
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>
> I thought the same thing when I saw the presentation at this year's 
> AWA convention in Rochester.  It thought is sounded more like trunking.
>
> Bill
>
> On 11/9/2015 5:13 PM, David Sica wrote:
>> Just remember
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>> Jim,
>>
>> You are likely (surely?) correct.  That's one thing I like about this 
>> group, there's always a real engineer around to correct what we 
>> shade-tree engineers think we know!
>>
>> -- Dave
>>
>>
>> New Jersey Antique Radio Club
>>
>> On Mon, Nov 9, 2015 at 3:42 PM, <antqradio at sbcglobal.net 
>> <mailto:antqradio at sbcglobal.net>> wrote:
>>
>>     Just remember
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>>     _________________________________________________________
>>
>>     I could be wrong on this but I think "frequency hopping" is a
>>     very different animal then "spread spectrum."
>>
>>     The former is used in cellphones with a constant "bandwidth" on a
>>     step changing carrier frequency assigned by the local cellphone
>>     tower control computer and the latter was Lamarr's contribution,
>>     essentially a very wide bandwidth and hopefully undetectable
>>     signal. Perhaps some wireless telephones used in the home use
>>     spread spectrum but not cellphones, at least not to my knowledge.
>>     Jim
>>
>>     ------------------------------------------------------------------------
>>     *From:* David Sica <dave.sica at njarc.org <mailto:dave.sica at njarc.org>>
>>     *To:* "njarc at mailman.qth.net <mailto:njarc at mailman.qth.net>"
>>     <njarc at mailman.qth.net <mailto:njarc at mailman.qth.net>>
>>     *Sent:* Monday, November 9, 2015 2:01 PM
>>     *Subject:* [NJARC] Hedy Lamarr (again)
>>
>>     Today's Google Doodle is in honor of Hedy Lamarr.    Known in her
>>     time as "the most beautiful girl in the world" she was also an
>>     inventor and held the patent for, among other things, the
>>     spread-spectrum technology underlying our present-day cell phone
>>     system.
>>
>>     http://www.google.com/doodles/hedy-lamarrs-101st-birthday
>>
>>
>>
>>
>>     Just remember
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>>
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