FM broadcast is 75kHz deviation with 15kHz of mono audio or 180kHz of bandwidth and the channel spacing has always been 400kHz. The HD sidebands are a single 100 to 150kbs digital channel that can be dived into separate streams and are only at 10% maximum of the analog power.
Broadcast FM channel spacing is 200 kHz with a maximum deviation of 75 kHz ether side of the center frequency. Analog/HD Hybrid bandwidth in the US is 400 kHz. Both HD sidebands are transmitting the same data information whether it be HD1 HD2 or HD3.
Get a small fm transmitter and send test audio signal into it and you can see how it all works..Be sure to use a attenuation pad and or dummy load as don't want to fry the analyzer.
you can see how IBOC is really inband on SOMEONE ELSES channel..... that is such a corporate lie the big corporate stations toss out this digital jamming signal on the next channel above and below there own analog channel.... such a scam..