# Reply to post: Re: Speed of light

### Halfords invents radio signals that don't travel at the speed of light

#### Re: Speed of light

yeah, and obviously a physics constant.

The quote in the article suggests that he should have said BANDWIDTH [for the modulation] and not "super-fast wavelength" implying "speed", but people who don't understand modulation won't get it, probably. [People in here probably WILL get it]

Whenever you modulate a carrier, you generate frequencies that are equal to the modulation frequency[ies] plus or minus the carrier frequency. In the case of FM, FSK, QAM, and other modulation methods, you have to include harmonics as well, and in theory, the harmonic output goes out to 'infinity' in both directions around the carrier frequency. [in practice it's limited by filters]..

16khz bandwidth (+/- 8khz) would be typical for an AM broadcast, up to ~8khz audio freq in the modulation. This gives you reasonable quality audio, good for voice [hence news/talk formats typical on AM].

+/- 75Khz bandwidth is typical for a wide-band FM broadcast. A total bandwidth of 75khz would have too much harmonic distortion (think 'missing information'). In the USA, there is a 200khz 'in between' frequency range between stations to allow for sufficient bandwdth without side-channel interference.

for QAM and FSK and spread spectrum and other digital modulation methods, you have a much higher bandwidth requirement, and 'frequency hopping', and things like that. Wifi, cell phones, digital radio and TV signals, all use something _like_ this. And of course, their bandwidth is in Mhz and not Khz, and can take up a pretty big chunk of the available spectrum. Hence, it's transmitted in the Ghz range where this kind of thing makes more sense.

Anyway, what the quoted marketeer was apparently TRYING to say is that wider BANDWIDTH means you can transmit MORE DATA at a higher DATA RATE.

but yeah he got it wrong in the details, concepts, and presentation.

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