Hi: Most cell phones and wireless internet 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? Let's say a DSSS/FHSS type of spread-spectrum is transmitted and received using the AM radio waves in the UHF spectrum [i.e. spread info for transmission throughout the UHF band and receive AM radio waves throughout all UHF frequencies]. What would be the disadvantages of this? Normally DSSS and FHSS are transmitted/received on FM radio waves. So I ask what would be the disadvantages of using AM instead of FM for this? AM radio tends to be more vulnerable to unwanted magnetic disruptions than FM, however this only affects analog reception. Digital reception on AM should be unaffected even by the strongest-interfering analog RF magnetic signal. Right? Thanks, Radium
Disadvantages of using AM for DSSS/FHSS?
Started by ●April 28, 2008
Reply by ●April 28, 20082008-04-28
On Apr 28, 5:26�pm, "Green Xenon [Radium]" <gluceg...@excite.com> wrote:> Hi: > > Most cell phones and wireless internet 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? > > Let's say a DSSS/FHSS type of spread-spectrum is transmitted and > received using the AM radio waves in the UHF spectrum [i.e. spread info > for transmission throughout the UHF band and receive AM radio waves > throughout all UHF frequencies]. What would be the disadvantages of this? > > Normally DSSS and FHSS are transmitted/received on FM radio waves. So I > ask what would be the disadvantages of using AM instead of FM for this? > > AM radio tends to be more vulnerable to unwanted magnetic disruptions > than FM, however this only affects analog reception. Digital reception > on AM should be unaffected even by the strongest-interfering analog RF > magnetic signal. Right? > > Thanks, > > RadiumCellphones moved away from FM when they dropped analog service. IDEN phones use a 4 subcarrier 16-QAM, but they are channelized and not spread spectrum.
Reply by ●April 28, 20082008-04-28
Green Xenon [Radium] wrote:> Hi: > > Most cell phones and wireless internet 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? > > Let's say a DSSS/FHSS type of spread-spectrum is transmitted and > received using the AM radio waves in the UHF spectrum [i.e. spread info > for transmission throughout the UHF band and receive AM radio waves > throughout all UHF frequencies]. What would be the disadvantages of this? > > Normally DSSS and FHSS are transmitted/received on FM radio waves. So I > ask what would be the disadvantages of using AM instead of FM for this? > > AM radio tends to be more vulnerable to unwanted magnetic disruptions > than FM, however this only affects analog reception. Digital reception > on AM should be unaffected even by the strongest-interfering analog RF > magnetic signal. Right? > > > Thanks, > > RadiumHi, FM demodulation produces a handy 'capture' effect. If a weak and a strong signal are present together, then the recovered baseband signal from the weaker FM signal is greatly reduced. This is useful in rejecting interference from adjacent stations on the same frequency. With AM, the demodulated baseband signals are present in amplitudes that are proportional to their RF amplitudes. In addition, the AM carriers will 'beat' together to produce an additional and unwanted tone-modulation of the received RF signal. Regards, John
Reply by ●April 28, 20082008-04-28
John Monro wrote:> Green Xenon [Radium] wrote: >> Hi: >> >> Most cell phones and wireless internet 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? >> >> Let's say a DSSS/FHSS type of spread-spectrum is transmitted and >> received using the AM radio waves in the UHF spectrum [i.e. spread >> info for transmission throughout the UHF band and receive AM radio >> waves throughout all UHF frequencies]. What would be the disadvantages >> of this? >> >> Normally DSSS and FHSS are transmitted/received on FM radio waves. So >> I ask what would be the disadvantages of using AM instead of FM for this? >> >> AM radio tends to be more vulnerable to unwanted magnetic disruptions >> than FM, however this only affects analog reception. Digital reception >> on AM should be unaffected even by the strongest-interfering analog RF >> magnetic signal. Right? >> >> >> Thanks, >> >> Radium > > Hi, > > FM demodulation produces a handy 'capture' effect. If a weak and a > strong signal are present together, then the recovered baseband signal > from the weaker FM signal is greatly reduced. This is useful in > rejecting interference from adjacent stations on the same frequency. > > With AM, the demodulated baseband signals are present in amplitudes that > are proportional to their RF amplitudes. In addition, the AM carriers > will 'beat' together to produce an additional and unwanted > tone-modulation of the received RF signal. > > Regards, > JohnBut if the signal is digital, won't it remain immune to EMI/RFI [analog disruption] even if received on AM? DSSS and FHSS and digital. So I would think that the analog magnetic interferences wouldn't affect it. Also, doesn't FM have the disadvantages in that it hogs more bandwidth than AM?
Reply by ●April 28, 20082008-04-28
clay@claysturner.com wrote:> On Apr 28, 5:26 pm, "Green Xenon [Radium]" <gluceg...@excite.com> > wrote: >> Hi: >> >> Most cell phones and wireless internet 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? >> >> Let's say a DSSS/FHSS type of spread-spectrum is transmitted and >> received using the AM radio waves in the UHF spectrum [i.e. spread info >> for transmission throughout the UHF band and receive AM radio waves >> throughout all UHF frequencies]. What would be the disadvantages of this? >> >> Normally DSSS and FHSS are transmitted/received on FM radio waves. So I >> ask what would be the disadvantages of using AM instead of FM for this? >> >> AM radio tends to be more vulnerable to unwanted magnetic disruptions >> than FM, however this only affects analog reception. Digital reception >> on AM should be unaffected even by the strongest-interfering analog RF >> magnetic signal. Right? >> >> Thanks, >> >> Radium > > Cellphones moved away from FM when they dropped analog service. IDEN > phones use a 4 subcarrier 16-QAM, but they are channelized and not > spread spectrum.Yeah but even if the signal being transmitted/received is digital, it's carrier wave is still analog. Right? AFAIK, there is no such thing as a digital carrier wave. The carrier wave is always analog just like a cable link is also always analog. The signal transmitted through the analog medium maybe digital, though. If a PCM signal [digital] is transmitted on an AM carrier wave [analog], the AM wave's peak-to-peak amplitude will vary according to the PCM signal in the following manner: 1. A positive amperage of the PCM signal will cause the AM carrier wave's peak-to-peak amplitude to increase while a negative amperage [i.e. going below the x-axis when graphed] will cause a decrease the AM carrier's peak-to-peak amplitude. 2. A increase in frequency of the PCM signal will cause the AM carrier's peak-to-peak amplitude to vary more rapidly while a decrease in the PCM signal's frequency will cause the AM wave's peak-to-peak amplitude to vary more slowly. That's how I understand it. The PCM signal is digital but causes a measurable affect on the analog AM carrier wave. Upon reception, an AM-demodulator can retrieve this PCM signal and play it back. I could be wrong though.
Reply by ●April 28, 20082008-04-28
Green Xenon [Radium] wrote:> DSSS and FHSS and digital.Sorry, that should read "DSSS and FHSS *are* digital."
Reply by ●April 28, 20082008-04-28
Don't feed the troll Bob Myers wrote: Radium has never actually had an original question. All of his questions are either rehashing very well-understood situations, or are utterly nonsensical and therefore not answerable AS legitimate questions. RHF wrote: Since Radium is an ignorant idiot, he has no clue what group would be appropriate for his moronic questions. Porgy Tirebiter wrote: You are a uneducated troll.... You blabber on and on about nothing. No one is interested in your opinions. Discover women or masturbation, stop playing on Usenet, we are not amused. Jim wrote: Belief doesn't make reality. A hundred years or so of experments say that's utter, babbling, nonsense. I'd suggest fluphenazine and haloperidol. Babbling, delusional nonsense. Seek help. There are drugs that may help your condition if you are treated early enough. Radium is a silly-ass, ignorant child. DTC (that's me) wrote This thread reminds me of situations where someone acquire a little knowledge of something and extrapolates it into areas of which they have a limited skill set for understanding them. Another example of Radium's mastery of trolldum is: Radium wrote: Can the Spin Exchange Relaxation Free Magnetometer be used to receiver distant AM radio signals in which the carrier frequency is 150 KHz? What if the carrier frequency is 44.1 KHz [for the same reason CDs use a 44.1 KHz sample rate]? 40 KHz? Thanks a bunch, Radium
Reply by ●April 29, 20082008-04-29
"Green Xenon [Radium]" <glucegen1@excite.com> wrote in message news:48164106$0$5109$4c368faf@roadrunner.com...> AM radio tends to be more vulnerable to unwanted magnetic > disruptions than FM, however this only affects analog > reception. Digital reception on AM should be unaffected even > by the strongest-interfering analog RF magnetic signal. > Right?I'm not sure how. All transmission is analog until the received signal is digitized. FM (and it's step-brother, FSK) offer better immunity to impulse noise than AM at the expense of spreading the transmitted power over the redundancy that exists in their spectra.
Reply by ●April 29, 20082008-04-29
"DTC" <me@nothingtoseehere.zzx> wrote in message news:DWvRj.11932$V14.1307@nlpi070.nbdc.sbc.com...> Don't feed the trollSome of you "Don't feed the troll" freaks are more objectionable than the OP. At least he asked a sensible question (whether or not he understands the answer). What, exactly, did you contribute?
Reply by ●April 29, 20082008-04-29
John E. Hadstate wrote:> > "DTC" <me@nothingtoseehere.zzx> wrote in message > news:DWvRj.11932$V14.1307@nlpi070.nbdc.sbc.com... >> Don't feed the troll > > Some of you "Don't feed the troll" freaks are more objectionable than > the OP. At least he asked a sensible question (whether or not he > understands the answer). What, exactly, did you contribute?Obviously you haven't kept up with his dribble over the past year.
