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Does the FCC restrict how much bandwidth an amateur radio operator can transmit? I've seen restrictions for transmitting data, like packet and ATV, but, for example, could I legally use a huge bandwidth like 500 kHz to transmit FM in the 2 meter band?

For example, studying for the extra class exam, I saw this:

The maximum bandwidth for data emission on 60 meters is 2.8kHz.

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Mostly, on HF, the FCC has chosen to limit modes of transmission and symbol rates rather than bandwidth (60 Meters is the exception, where they have limited both bandwidth and mode). For instance, you are currently allowed to use FM only on 29MHz and above, regardless of the bandwidth used. But on VHF and above, there are no legal limitations of bandwidth.

So technically, yes, if you had a wide deviation FM transmitter you could use it on 2 meters. Although as I'm sure you know this would be very irresponsible [but not illegal according to current FCC rules.]

On 10GHz and similar high bands with tons of space, it is commonplace to use wideband FM (normally a bandwidth of 200-300kHz). This allows equipment to be used with less than optimal frequency stability (which is very difficult to obtain at those high frequencies).

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  • $\begingroup$ Yes, I just picked 500 kHz out of a hat. That would indeed be irresponsible. I'm actually somewhat surprised the FCC isn't more strict on this, but perhaps in the future, when SDR transmitters will be even more common/popular than they are now, it would seem people could easily (or inadvertently) do such a thing, and the FCC would probably start putting bandwidth restrictions on all bands. $\endgroup$
    – Geremia
    Commented Jan 9, 2017 at 19:43
  • $\begingroup$ Yes an SDR transceiver could do it, or for that matter a conventional one, without trouble. So if there was a legitimate use for it, it would technically be legal, but I'm sure there are better solutions :-) $\endgroup$
    – ruhnet
    Commented Jan 9, 2017 at 19:46
  • $\begingroup$ I asked the question to your answer here. ☺ Perhaps you can paste your comment here as an answer to my question there. $\endgroup$
    – Geremia
    Commented Jan 9, 2017 at 20:25
  • $\begingroup$ There is a blanket rule (§97.101(1)) that transmissions must conform to "good amateur practice". As such "very irresponsible" means "illegal". $\endgroup$
    – Phil Frost - W8II
    Commented Jan 9, 2017 at 21:31

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