False triggering of HD Radio?

[KB1OKL]

I think this discussion is interesting perhaps but moot as HD will be a distant memory in a few years anyway, is similar (at this point in time anyway) to wondering if the new Chevy Impala V8's will break the 600HP mark next year (can dream right?).

Incidentally I just sent off an e-mail to a west coast AM DX club asking their opinion of AM stations traveling all the way to Australia

 

[KB1OKL]

I got this reply:

"Hi Bob,
Years ago from Phoenix, I received digihash from WOR, New York's tests, even
though its on-air analog signal was covered up by other stations.
This leads me to believe that the Australian reception is indeed possible."

 

[stormy01]

Sorry - I should have explained that in Pure Digital Mode on the Medium Wave
band, most of the Digital power would then be within the 10kHz bandwidth, not
on the sidebands as it is now in Hybrid-Digital. No wonder one could get alarmed
that a station with 5kW Digital Power on its sidebands would obliterate any other
station for hundreds and hundreds of miles (if not more) - of course it would!


Check this article out - http://en.wikipedia.org/wiki/HD_Radio

I think what the author(s) are stating in the above referenced article is entirely
possible, though the codecs need to be improved even further in order to derive
decent sounding audio an average 30k bit rate! At the present time 30kb audio
only sounds adequate - and I mean anywhere: internet streaming, satellite radio
or Hybrid Digital terrestrial radio. Give it time - 30kbits now sounds a lot better
now than it did even 5 years ago!

"When operating in pure digital mode, the AM-HD Radio signal fits
inside a standard 10 kHz channel (20-40 kbit/s) or an extended 20 kHz
channel (40-60 kbit/s), at the discretion of the station manager.[8]"

see iBiquity Digital Corporation - IBOC White Papers

http://www.ibiquity.com/broadcasters/quality_implementation/iboc_white_papers


However, AM HD Radio signal in full digital mode is 15dB (32 times)
higher in digital power compared to that in hybrid digital mode and
coverage is expected to approximate the previous analog coverage.


32 times the power of Hybrid 32 * 500 watts = 16,000 watts

(so my idea of 5kW Full Digital instead of 50KW Analog was a conservative
estimate; 5kW would be a 10 fold, or 10dB increase) My guess is that
improved receiver sensitivity and selectivity and the transmitting channel
confined to a standard bandwidth of 10KHz would be helpful in reducing
interference.

If almost all of the digital energy is confined to a 10kHz bandwidth, then
there would be little to no interference to a station 10 kHz away from the
"offending" station. But that is only going to be possible on a full digital
signal, of course!

That would be nice, however, with the number of stations on the air, the FCC is unlikely
to allow a larger footprint in digital than in analog (think: market service area)...the current
50kW AM stations will probably be allowed no more than 5kW

If the current sidebands on AM are the same as FM - 1/100 the power - then 5kW would be a tremendous power increase for AM! What astonishes me is how 50kW / 100 = 500 W, yet those sidebands go 1000 miles in the daytime! Even in a noisy area like Dallas, WOAI sidebands are much louder than WOAI analog - at only 500W! Put 5 kW on those sidebands and local 1190 goes bye-bye during the daytime. WOAI full digital, even at only 5 kW, will be audible coast to coast. All other 1200's - jammed.

 

[rbrucecarter5]

However, AM HD Radio signal in full digital mode is 15dB (32 times)

Very good analysis. The original thread was whether HD in the US could cause an HD receiver in Australia to at least turn on the HD indicator. There was some mention of "like AM stereo" - but it is my understanding that the AM stereo indicator was just triggered by a 25 Hz tone, any number of things like heterodynes from stations on either side could cause a flicker of the AM stereo indicator. Isn't lighting the HD indicator a much more involved process, requiring real digital sidebands to be present with the proper characteristics? Therefore, it would be very unlikely to get "false trigger?

 

[KB1OKL]

Sorry - I should have explained that in Pure Digital Mode on the Medium Wave
band, most of the Digital power would then be within the 10kHz bandwidth, not
on the sidebands as it is now in Hybrid-Digital. No wonder one could get alarmed
that a station with 5kW Digital Power on its sidebands would obliterate any other
station for hundreds and hundreds of miles (if not more) - of course it would!


Check this article out - http://en.wikipedia.org/wiki/HD_Radio

I think what the author(s) are stating in the above referenced article is entirely
possible, though the codecs need to be improved even further in order to derive
decent sounding audio an average 30k bit rate! At the present time 30kb audio
only sounds adequate - and I mean anywhere: internet streaming, satellite radio
or Hybrid Digital terrestrial radio. Give it time - 30kbits now sounds a lot better
now than it did even 5 years ago!

"When operating in pure digital mode, the AM-HD Radio signal fits
inside a standard 10 kHz channel (20-40 kbit/s) or an extended 20 kHz
channel (40-60 kbit/s), at the discretion of the station manager.[8]"

see iBiquity Digital Corporation - IBOC White Papers

http://www.ibiquity.com/broadcasters/quality_implementation/iboc_white_papers


However, AM HD Radio signal in full digital mode is 15dB (32 times)
higher in digital power compared to that in hybrid digital mode and
coverage is expected to approximate the previous analog coverage.


32 times the power of Hybrid 32 * 500 watts = 16,000 watts

(so my idea of 5kW Full Digital instead of 50KW Analog was a conservative
estimate; 5kW would be a 10 fold, or 10dB increase) My guess is that
improved receiver sensitivity and selectivity and the transmitting channel
confined to a standard bandwidth of 10KHz would be helpful in reducing
interference.

If almost all of the digital energy is confined to a 10kHz bandwidth, then
there would be little to no interference to a station 10 kHz away from the
"offending" station. But that is only going to be possible on a full digital
signal, of course!

That would be nice, however, with the number of stations on the air, the FCC is unlikely
to allow a larger footprint in digital than in analog (think: market service area)...the current
50kW AM stations will probably be allowed no more than 5kW

If the current sidebands on AM are the same as FM - 1/100 the power - then 5kW would be a tremendous power increase for AM! What astonishes me is how 50kW / 100 = 500 W, yet those sidebands go 1000 miles in the daytime! Even in a noisy area like Dallas, WOAI sidebands are much louder than WOAI analog - at only 500W! Put 5 kW on those sidebands and local 1190 goes bye-bye during the daytime. WOAI full digital, even at only 5 kW, will be audible coast to coast. All other 1200's - jammed.

This would be fine on a new band that was opened up expressly for digital transmission, but to obliterate the FM and especially the AM band with HD noise is ridiculous.