The Natural Philosopher wrote:


> In the limit, any modulation regime you use, results in changes in the
> amplitude/frequency spectrum: broadcast FM only HAS a better S/N ratio
> and capture effect BECAUSE it occupies so much spectrum.


But wouldn't a digital system using AM be unaffected by the unwanted
EMI/RFI that would normally hinder analog AM?


>
> For example, consider - say - a modulation in which say 8 digital bits
> correspond to 8 different frequencies. As the data is sent, the
> frequency 'hops'' from one frequency to another.
>
> However,that is exactly the same as having one transmitter that is
> frequency modulated, or 8 transmitters that are amplitude modulated, on
> different frequencies.


I prefer the former over the latter. I've never heard of analog EMI/RFI
signal interfering with digital signal reception. So I'd have to say
multiple AM transmitters on different frequencies would yield better
results than one FM transmitter.


> Modulation schemata are chosen with an eye to the type of interference
> likely to be encountered: multipath for example makes a mockery of phase
> shifts, and makes single frequency working liable to peaks and nulls. A
> wider spectral energy helps defeat multipath, and single frequency
> interference sources, especially with some digital schema imposed on top.
>
> That's why its done.


But wouldn't multipath interference be as much of an issue in FM as in AM?