Mark Roberts wrote:

What's next: analog radios with 2 kHz bandwidth so we don't hear the
buzzing noise placed there to serve receivers that don't exist?!?!?

I suspect this is the back door through which DRM will slip for
broadcast radio.


I STILL would like to know why we actually need IBOC.
On my car radio with AM stereo it sounded great.
Not to shabby either after the NRSC mask was mandated. But then who
really listens to AM for music?

Analog FM if processed reasonably is capable of holding its own
against the original product. I can see the advantage of IBOC
for FM, but not AM. I suspect the whole subject is just a scam
for someone to make money (hardware & licensing) and a way to
slip a *broadcast flag* on everything so it can't be copied.


Charlie

On 13 Jul 2004 04:34:38 GMT, Garrett Wollman ("Garrett") writes:
Garrett People I talk to in *my* business (computing, not broadcasting)
Garrett are of the opinion that traditional, reserved-spectrum broadcasting
Garrett will cease to exist inside of three decades, for various reasons,
Garrett social as well as technological. (That's assuming it isn't already
Garrett dead -- many of the people I know, my age and younger, are simply
Garrett no longer users of radio at all. It doesn't connect with them in
Garrett any meaningful way, nor does it serve their needs.)

Specifically, your "business" is computer systems support at
a techie university, so I am guessing that the people you're
referring to are students? (If that's not the kind of people
you're talking about, could you describe who you mean?)

Most of the people I know at MIT don't to any AM radio, but they
may listen to a few NPR shows. Entertainment is mostly not from
the radio: music is on portable media or file-sharing networks.
But MIT students (in my few decades of experience with them) are
particularly un-representative of popular culture or societal norms.
I think you would find that the people of the same age across the
river at BU to have somewhat different behaviours. When you say
that it "no longer" servers their needs, I think maybe you're just
suggesting that they now live on campus or in the tiny walking city
(with demographics unlike anywhere else in the country, anyway),
they don't like talk radio, don't drive cars, and are very busy studying.
I would not base a prediction of whether people will be interested
in broadcasting on the behaviour of MIT students, because they've
never been very interested in popular commercial broadcasting,
as it has never really served the needs of the uber-nerd subculture.

What shows do you listen to while driving in your car,
and what do you do for traffic reports, and how do you
get your local news and weather on video or while driving?

But I would be interested in hearing technical and societal arguments
about how traditional broadcasting won't be interesting or viable in
the near future, or even in 30 years. (2035 is a long ways off, and
I think there could be major technological changes by that time which
could affect how broadcasting works.)

Charlie had written:
| Mark Roberts wrote:
|
| What's next: analog radios with 2 kHz bandwidth so we don't hear the
| buzzing noise placed there to serve receivers that don't exist?!?!?
|
| I suspect this is the back door through which DRM will slip for
| broadcast radio.
|
|
| I STILL would like to know why we actually need IBOC.
| On my car radio with AM stereo it sounded great.
| Not to shabby either after the NRSC mask was mandated. But then who
| really listens to AM for music?

In San Francisco, if you want to hear an MOR station, you either
have an NCE-FM that has some limited coverage, or you have an AM
station (KABL) that still broadcasts in stereo.

In other cases, some specialty formats, mostly of the ethnic
variety, are available only on AM -- an exactly reversal of the
situation vis-a-vis FM 40 to 50 years ago.

| I suspect the whole subject is just a scam
| for someone to make money (hardware & licensing) and a way to
| slip a *broadcast flag* on everything so it can't be copied.

Precisely! The control freakery being exerted by content providers
is just going to end up chasing people away from the media.

--
Mark Roberts |"Bush campaign ads boast that 1.5 million jobs were added in the
Oakland, Cal.| last 10 months, as if that were a remarkable achievement. It
NO HTML MAIL | isn't. During the Clinton years, the economy added 236,000 jobs
in an average month." -- Paul Krugman, NY Times, 7-6-2004

"Charlie" wrote in message ...
Mark Roberts wrote:

What's next: analog radios with 2 kHz bandwidth so we don't hear the
buzzing noise placed there to serve receivers that don't exist?!?!?

I suspect this is the back door through which DRM will slip for
broadcast radio.


I STILL would like to know why we actually need IBOC.
On my car radio with AM stereo it sounded great.
Not to shabby either after the NRSC mask was mandated. But then who
really listens to AM for music?

Analog FM if processed reasonably is capable of holding its own
against the original product. I can see the advantage of IBOC
for FM, but not AM. I suspect the whole subject is just a scam
for someone to make money (hardware & licensing) and a way to
slip a *broadcast flag* on everything so it can't be copied.

That's my take, too. I had no trouble getting an AM audio chain to sound pretty darn
good, mono or stereo, a situation which, from the assessments here (as well as the
samples provided by...was it Ron?) can't compare to what IBOC leaves you with.

The irony about your suggestion that IBOC is just a scam to get programming locked
down is that who would want to save the garbage that IBOC creates?

I gotta tell you....had I not quit the business in the 80s, I'd probably do so now.
There's just no future in it, considering the crackerjacks who are pushing this
"innovation". IBOC is D-O-A.
--
-----------------------------------------------------------------------------
There must always be the appearance of lawfulness....especially when the law's being
broken.
-----------------------------------------------------------------------------
For direct replies, take out the contents between the hyphens. -Really!-

Scott Dorsey had written:
| Mark Roberts wrote:
|
| If AM IBOC is such hot stuff, why is it restricted to daytime hours only?
|
| Because the group delay that is the result of the uneven ionosphere prevents
| it from being decoded properly when the signal is received on skip, and the
| amount of stuff coming over the horizon on skip prevents it from being
| properly received when it's being received on groundwave at night.

I didn't quite expect an answer to a rhetorical question -- but it does
point to a very fundamental flaw in the scheme.


--
Mark Roberts |"Bush campaign ads boast that 1.5 million jobs were added in the
Oakland, Cal.| last 10 months, as if that were a remarkable achievement. It
NO HTML MAIL | isn't. During the Clinton years, the economy added 236,000 jobs
in an average month." -- Paul Krugman, NY Times, 7-6-2004

In article , says...


In article ,
Mark Roberts wrote:

On a synchronous detector, it sounds worse...like a mosquito buzzing
in the background.

That's because it's in quadrature, which is "invisible" (modulo
transmission artifacts and channel noise) to envelope detectors. Your
sync. detector is only detecting one sideband at a time, so the IBOC
carriers don't cancel out.

You have this exactly wrong. Envelope detectors are not sensitive to
the phase of the carrier, responding instead to the square root of the sum
of the squares of the I and Q components of the modulation:

SQRT(I^2 + Q^2)

(The carrier must be present in order to properly bias the envelope
detector, but, upon demodulation, the carrier simply appears as a DC term.)

A synchronous detector will detect either the I channel or the Q channel (or
some linear sum of the two) depending on the phase of the regenerated
carrier. It can be configured to reject the Q channel entirely by ensuring
that the regenerated carrier is precisely in-phase with the original
carrier.

To detect single sideband, you need two synchronous detectors whose carrier
inputs are in quadrature and whose IF inputs are also in quadrature. A
single synchronous detector will _not_ detect single-sideband.

See any textbook on modulation theory.

In article , says...


Mark Roberts wrote:

If AM IBOC is such hot stuff, why is it restricted to daytime hours only?

Because the group delay that is the result of the uneven ionosphere prevents
it from being decoded properly when the signal is received on skip, and the
amount of stuff coming over the horizon on skip prevents it from being
properly received when it's being received on groundwave at night.


I do not believe that this is correct. The modulation scheme of iBiquity's
IBOC system is basically multiple carrier COFDM, and is quite similar to the
modulation scheme used in Digital Radio Mondiale (DRM), which is known to be
robust in the face of selective fading. It all depends on the symbol spacing
used in the COFDM carriers. If the multipath period is shorter than the
symbol spacing, then the various reflections will reinforce. Because there
are multiple narrowband carriers in COFDM, the data rate on each carrier can
be very low (allowing long symbol spacing), yet the presence of multiple
carriers still allows the overall system to deliver a high data rate.

In article ,
Mark Roberts wrote:
Scott Dorsey had written:
| Mark Roberts wrote:
|
| If AM IBOC is such hot stuff, why is it restricted to daytime hours only?
|
| Because the group delay that is the result of the uneven ionosphere prevents
| it from being decoded properly when the signal is received on skip, and the
| amount of stuff coming over the horizon on skip prevents it from being
| properly received when it's being received on groundwave at night.

I didn't quite expect an answer to a rhetorical question -- but it does
point to a very fundamental flaw in the scheme.

Sorry, I can't seem to find Bob Orban's reply to this. But I agree with
Bob that the encoding scheme is very robust about dealing with group delay
issues. Even so, I have found the actual skip performance poor to the
point of unusability.

Bob, do you have a citation on any actual measurements of this stuff?
Ionosonde data is easy to get, so it should be really easy to build a
simulation of ionospheric distortions in matlab or something, even if you
just take into account group delay and multiple reflections. Has anyone
actually done any simulations on the current encoder to see how it survives
under various simulated skip conditions? I'd be curious to see which of
the various skip characteristics is the most serious issue.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."