Disadvantages of using AM for DSSS/FHSS Spread Spectrum?
 

wrote:
What part of "To greatly simplify" are you having problems understanding?

"Everything should be made as simple as it is,
but not simpler." Albert Einstein.
--
73, Cecil http://www.w5dxp.com

Disadvantages of using AM for DSSS/FHSS Spread Spectrum?
 

Roy Lewallen wrote:
"You really should try ro understand the context of the various
quotations from Terman."

I do.

I did not give the quotation from Terman, only its gist. Here it is:
"A useful rule is that a frequency modulated wave contains sideband
components of importance on either side of the carrier wave over a
frequency interval approximating the sum of the frequency deviation and
the modulating frequency. The total bandwidth in which most of the wave
is contained is then twice this value."

The original posting in this thread read:
"Most cell phones and wireless routers, modems, and access points that
use spread spectrum usually broadcast and receive their data on FM-radio
waves. Just out of curiosity, I ask why not use AM?"

Nothing about narrow-band FM in the question and I responded:

"---losing insensitivity to carrier level when recovering modulation."

I did not take Terman out of context to distort his meaning. Ternan was
merely restating Carson`s rule which is the same approximation the FCC
uses to determine bandwidth. I quoted this in my May 2, 3:28 pm posting.
I`ve used this to calculate bandwidth many times with no citations from
the FCC yet.

I make plenty of mistakes but I see only one I`ve made in my postings in
this thread and that is an instance where I typed FM when I meant AM and
I immediately corrected it in the next posting.

Best regards, Richard Harrison, KB5WZI

Disadvantages of using AM for DSSS/FHSS Spread Spectrum?
 

Richard Harrison wrote:
Roy Lewallen wrote:
"You really should try ro understand the context of the various
quotations from Terman."

I do.

I did not give the quotation from Terman, only its gist. Here it is:
"A useful rule is that a frequency modulated wave contains sideband
components of importance on either side of the carrier wave over a
frequency interval approximating the sum of the frequency deviation and
the modulating frequency. The total bandwidth in which most of the wave
is contained is then twice this value."

The original posting in this thread read:
"Most cell phones and wireless routers, modems, and access points that
use spread spectrum usually broadcast and receive their data on FM-radio
waves. Just out of curiosity, I ask why not use AM?"

Nothing about narrow-band FM in the question and I responded:

"---losing insensitivity to carrier level when recovering modulation."

I did not take Terman out of context to distort his meaning. Ternan was
merely restating Carson`s rule which is the same approximation the FCC
uses to determine bandwidth. I quoted this in my May 2, 3:28 pm posting.
I`ve used this to calculate bandwidth many times with no citations from
the FCC yet.

I make plenty of mistakes but I see only one I`ve made in my postings in
this thread and that is an instance where I typed FM when I meant AM and
I immediately corrected it in the next posting.

Best regards, Richard Harrison, KB5WZI

How did you conclude from this statement in Terman that the bandwidth
required by FM is twice that required by AM?

Roy Lewallen, W7EL

Disadvantages of using AM for DSSS/FHSS Spread Spectrum?
 

Roy Lewallen wrote:
"How did you conclude from this statement in Terman that the bandwidth
required by FM is twice that required by AM?"

Easy, I turn up the peak deviation intil twice the bandwidth is occupied
with FM as would be required for AM. It is arbitrary and depends on peak
deviation. If you make the deviation less than half the modulating
frequency, the bandwidth occupied will be about the same as required for
AM.

Best regards, Richard Harrison, KB5WZI