[IRCA] Another perspective on AM IBOC, from the broadcasters' mailing list

[Scott Fybush <scott@xxxxxxxxxx>]

This caught my attention over on the [BC] mailing list, and I suspect it 
may stir up some discussion on the DX lists:

> I have been investigating some of what has been said on this
> list about IBOC on AM. It appears as though it is really a
> receiver problem. Don't get me wrong. I'm not advocating
> trashing 150 bazillion conventional AM radios so that IBOC
> will work. Instead, as I am beginning to understand the
> technology, if an AM radio was designed with more modern
> technology, digital demodulation of AM with a wall filter,
> there would be no buzz. There really is plenty of bandwith
> available for IBOC on AM. The feds were not bamboozled.
> The problem is that AM radios of conventional design,
> superheterodyne with envelope detectors, cannot handle the
> adjacent channel IBOC interference at reasonable cost.
> 
> What the industry really needs is a decent AM radio using
> modern technology. Such a radio would directly digitize
> incoming spectra. AM would be demodulated by multiplication
> of the digitized data with the selected frequency. The
> resulting 'garbage' would be subjected to a FFT, the bins
> outside 10 kHz zeroed out, then the inverse FFT would be
> taken. The result would be a very clean AM signal with
> no response beyond the 10 kHz passband (9 kHz for some
> foreign countries), and no intermodulation from out-of-band
> responses. The same kind of preselection would be used for
> IBOC digital. You just don't demodulate the AM signal to
> baseband before digital processing. When I say
> "no intermodulation," I am talking 96dB down. Since a
> typical S/N of off-the air AM signals seldom exceeds
> 60dB, the intermodulation is 30 dB below the noise so,
> in fact, it is truly "no." Sixteen bits is 65536:1 =
> 20 log (65536) = 96.32 dB
> 
> In the past, such a receiver was incredibly expensive.
> Nowadays, we have inexpensive components that can handle
> these low bandwidth signals at very low cost. Remember
> that "real-time" for AM is 10,000 changes per second --
> truly trivial. For accurate replication of the RF
> component, you would need to sample something like 10
> times over-sampling. This means you need a 20 MHz 16-bit
> ADC. These things are now cheap, $35.00/1000. You can
> even get a whole development system for $158.00!
> Goodle "16-bit DAC 20 MHz" and see for yourself. Once
> somebody starts producing a million radios per month
> the price would likely drop to the $5.00 range.
> 
> So, I think that instead of complaining that the new
> technology is not compatible with 85 year-old radio
> design, some entrepreneur(s) should take the bull by the
> horns and develop a decent radio. They don't actually
> need to get such a radio into production. Leave that
> for the Pacific rim. What they need to do is generate
> the "IP" intellectual property with as much as possible
> embedded into a single chip. Then they license this
> technology and, perhaps, the chip design. There are
> lots of "radio" engineers who are now quite versed
> in software. A development kit and some (sometimes
> not too) pleasant software debugging time, would
> establish the viability of the digital radio approach
> for conventional AM. Then you could attract some
> investors. All words and ideas presented here are
> placed into the Public Domain. Get to work!
> 
> In the meantime, read my book:
> http://www.AbominableFirebug.com
> 
> Cheers,
> Dick Johnson

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