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The Beginning of the HD Radio Conquest of the Bands

rbc said:
I mean in the case of a hybrid station that goes all-digital. The range of the digital side-bands for that station should increase, because they no are longer sharing the power and spectrum budget with the analog signal.
Click to expand...

One would think that would be the case, but unlike AM the FM system doesn't seem to work that way. There is a 20db "hole" in the spectrum on channel, and the major power still occupies the adjacent channels. At least that's what it shows on page 8 of this document:

https://www.nrscstandards.org/standards-and-guidelines/documents/archive/nrsc-5-c/1026sf.pdf

The rules for spurious emissions are covered in 73.317:

https://www.law.cornell.edu/cfr/text/47/73.317

But I don't know how you measure db down from the carrier when there's no carrier any more, and if you increase the power of those sidebands to the power level that was previously licensed to the carrier there will be some severe interference issues to adjacent-channel stations. Clearly there is some additional work to do before FM can be "all digital".

Dave B.
 
DaveBayArea said:
One would think that would be the case, but unlike AM the FM system doesn't seem to work that way. There is a 20db "hole" in the spectrum on channel, and the major power still occupies the adjacent channels. At least that's what it shows on page 8 of this document:

https://www.nrscstandards.org/standards-and-guidelines/documents/archive/nrsc-5-c/1026sf.pdf

The rules for spurious emissions are covered in 73.317:

https://www.law.cornell.edu/cfr/text/47/73.317

But I don't know how you measure db down from the carrier when there's no carrier any more, and if you increase the power of those sidebands to the power level that was previously licensed to the carrier there will be some severe interference issues to adjacent-channel stations. Clearly there is some additional work to do before FM can be "all digital".

Dave B.
Click to expand...

Interesting. It almost seems like all-digital on the FM band was left to figure out later. That's a guess. That's consistent with some of the other remarks made on this thread.
 
I'm kind of curious about the basis for the 20 dB "hole" in the FM band all-digital. Is it intended to reduce interference to other stations sharing the channel that are still running an analog signal?
 
According to the note below the table on page 9, the region 100 kHz either side of center channel is reserved for "secondary low-level subcarriers". That might account for the indication of the 20-dB notch.
 
awsherrill said:
According to the note below the table on page 9, the region 100 kHz either side of center channel is reserved for "secondary low-level subcarriers". That might account for the indication of the 20-dB notch.
Click to expand...

This. The "hole" was to accommodate stations which ran 67kHz and/or 92kHz analog subcarriers (SCA). Although.. Anyone trying to run analog SCA's with digital carriers right next door should consider a different line of work.
 
True, IBOC has been dead for years, just that for some reason people still waste money on it, time for it to lie down for it's eternal rest
 
If I had an AM music station with at least one translator that at least duplicated my AM coverage, I would use the AM for an STL to feed the translator(s) since no one listens to the AM anyway. Do any stations do this? I realize that digital links always add annoying delays.
Thoughts?
 
ai4i said:
If I had an AM music station with at least one translator that at least duplicated my AM coverage, I would use the AM for an STL to feed the translator(s) since no one listens to the AM anyway. Do any stations do this? I realize that digital links always add annoying delays.
Thoughts?
Click to expand...

I don't believe you mean to take the AM signal, receive it at the FM site and rebroadcast it?

The deterioration of audio quality would be enormous.
 
KB1OKL said:
True, IBOC has been dead for years, just that for some reason people still waste money on it, time for it to lie down for it's eternal rest
Click to expand...

It is very useful to hundreds and hundreds of stations which then use the HD service to rebroadcast on a translator. Further, many public stations use HD 2 and beyond for things like classical, jazz and other features. And in larger markets, there are HC channels for native speaker of Persian, Russian, Iranian and other languages of immigrants.

While HD is not the success some envisioned, it is definitely an added arrow in the radio quiver.
 
DavidEduardo said:
While HD is not the success some envisioned, it is definitely an added arrow in the radio quiver.
Click to expand...

As I said in another thread I see it as similar to video diginets that TV stations offer as subchannels on their OTA channels. Most people can't receive them without a roof antenna. Cable companies usually only carry one of the three subs, and usually bury it far away from the main channel. But TV stations still operate them, typically as automated operations.
 
DavidEduardo said:
I don't believe you mean to take the AM signal, receive it at the FM site and rebroadcast it?
The deterioration of audio quality would be enormous.
Click to expand...
Woops, my bad!
I meant in the ALL DIGITAL MODE.
(this is an HD forum)
 
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