[digitalradio] A closer look at ROS]]
Tom Azlin N4ZPT
n4zpt at cox.net
Mon Feb 22 16:54:03 CST 2010
I would slightly modify your words to say that SS is when you make the
final signal many times the width of the original data signal. So a 100
bps data signal might be spread 30 times with a pseudo random sequence
and either directly spread or frequency hopped to be 3,000 hertz wide
thus picking up 10 dB spreading gain. Or might have enough error
correction added to be 30000 hertz wide. Which might actually be better
than 10 dB decoding gain.
Or is there no free lunch.
73, Tom 4zpt
On 2/22/2010 5:45 PM, Mike O'Dell wrote:
> the mere addition of redundancy isn't sufficient to make it
> spread-spectrum. anyone have his copy of Dixon handy? i'm sure
> there's probably a useful definition in there and that would more
> than likely be the one in everyone's mind "back when".
> doing forward error correction certainly adds redundancy but
> even the most obstreperous pedant would have trouble making
> a convincing argument that it constituted
> "spread-spectrum" if it was still contained within the
> bandwidth of a "communications-grade voice channel."
> I would require a definition of Spread-spectrum to include
> the notion that the final signal is many multiples of the
> bandwidth of a "communications-grade voice channel".
> On 2/22/10 4:17 PM, Tom Azlin N4ZPT wrote:
>> Hi Andre,
>> Still does not answer my question. What was the concern at the time
>> AMRAD was working SS approvals. If a signal were inside a 3KHz voice
>> grade bandwidth would those original fears be applicable?
>> I certainly accept that there is no free lunch. that is my favorite
>> systems trade comment.
>> 73, Tom n4zpt
>> On 2/22/2010 1:54 PM, Andre Kesteloot wrote:
>>> Sent from my iPhone (apparent spelling errors are due mainly to the
>>> thickness of my index and the size of the iPhone keyboard).
>>> On Feb 22, 2010, at 11:31, Tom Azlin N4ZPT<n4zpt at cox.net> wrote:
>>>> Spreading is adding known redundancy otherwise you would not get
>>>> spreading gain.
>>> Alas, there is no such thing as a free lunch.
>>> You only get spreading "gain" because you first introduced spreading
>>> André N4ICK
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