Update: Additional cites
> Jim
> Where did you get the diagram from?
I extracted those images from a pdf document authored by a
couple of Harris engineers; I think my previous post has a
link to the orginal pdf file on the Harris web site. That
document was primarily concerned with the Linearity Performance
of AM Transmitters to be used with various HD and digital (DRM
included) radio and touched on the spectral content just to
refresh some memories of those reading that document.
> I took the Ibiquity HD seminar and did not see that in any
> of my paperwork.
> I will look again.
> From what I understand. You can receive either the upper
> or lower digital sideband, and the Digital will work
> because both sidebands contain the same Information. You
This is true for HD IBOC mode "MA1", where the "P1" data stream
is transmitted over both the upper and lower "Primary" digital
sidebands.
Service mode "MA2" provides a higher throughput than MA1 at the
expense of robustness (duplicate or redunant data) as the data
stream "P1" which was transmitted on both upper and lower Primary
digital sidebands is *now* only transmitted on the lower "Primary"
digital sideband and "P2" data stream is transmitted over the upper
Primary sideband.
Now, depending on the BW of the analog audio transmitted various
factors come into play: the fidelity may change, different artifacts
may begin to appear and a 'blend' of digital and analog signals
may appear in the speakers ... as the OFDM carriers are 'dirtied'
by static crashes, power line noise, adjacent station splatter, and
the station's own transmitted analog signal that interferes with
the lower-level "P3" datastream (in the Seconday and Tertiary digital
sidebands).
> will just hear it at the lower(1/2) the bitrate
Well, it doesn't seem to be as simple as that; the 'robustness' of
the data transmittal seems to be affected more than anything, and
depending on the mode set the service (mono/stereo) may be affected
as well ...
This transmission mode is *heavy* with FEC (Forward Error Correction)
and bit stream interleaving that can negate most of the effects of
noise and selective fading; I did a bit of work involving Convolutional
error correctting codes some years back, and yes, you can lose
significant 'chunks' of data (not ALL of it, but random parts and
brief spurts).
> I dont have the paperwork infront of me but lets say each
> sideband is 8kb
> to hear the Full quality 16kb digital you need Both
> sidebands.
>
> Here is where I see the problem. some stations will have
> full digital bandwith Others will not. A good example is
> here in New Jersey you have 1660 and 1680
In any case, the "Primary" digital sidebands (both upper and lower)
that occupy the 'channel' at the <u>channel edges</u> are the culprits
that cause the most IBOC 'noise' to other stations.
I don't understand term 'full digital' here in the context of a hybrid
(analog + digital) HD IBOC station ... especially in light of the fact
that the HD IBOC modes "MA3" and "MA4" are 'full digital' and transmit
*no" analog signal *but* the strongest digital sidebands now occupy the
are close to the carrier where the analog signals exist in a hybrid or
analog-only station - this will have the effect of moving those 'noisy'
sidebands that are aways away from the assigned center channel to spots
closer in to the center of the assigned channel (and away from the
adjacents), and yielding a channel more akin to an analog-only station
that play lots of 'highly compressed' full spectrum music ...
> If both went IBOC they Both would have a digital sideband
> on 1670, and they are Both Overlap coverage area into
> northern NJ.
> you will NOT be able to listen to Both sidebands for Full
> Digital on these 2 stations. So why bother. Im not a betting
> Person Unless I know Im Right.
> and Im willing to Bet that If Either station went IBOC and
> the Other did not.
> The Digital from one will Slam the other...
> Fact. when Ibiquity was testing on 1700 from their NJ HQ
> with a "50watt experimental transmitter" that we know as a
> fact was Running 100watts as Per one of Ibiquitys own
> Engineers told us. It slammed 1680 for about 3 miles around
> their testing site. 1680's phones rang off the hook with
> Complaints But was told to Ignore them from the parent
> company Because they gave Ibiquity permission to test. I had
> to listen to My Boss however it did Not make me a happy
> camper as the station lost many listeners in the area. BTW
> the test station was Right in the 1680 Primary
> Contour.Probably could get Fired for making waves but I
> speak the truth. Apparently something many people Forget
> about. As for IBOC On AM. I call it smoke and mirrors
I think that HD IBOC hybrid mode has more application to FM
than AM, as there are factors to be considered that make such a
high-constant-BW-occupancy mode as a 'digital' signal on the
AM broadcast band highly incompatible with a) the current
AM band plan (ch assignment BW), b) current user equipment and
c) the propagation modes experienced.
Such 'tight' channel assignments works on radio systems that use
modes as FM (as the original AMPS cellular system did where a
minimum 17 dB C/N ratio was required); works on digital Cellular or
the PCS bands as a result of the subscriber/user equipment that is
designed to meet 'toll' quality speech BW requirements and do so with
low-data rate speech codecs and FEC - a similar problem exists today
with both analog TV and the AM broadcast bands where
interfering
carriers must be reduced 35 dB (or more) as determined in Mean
Opinion Scoring tests in order to render good, clean perceived audio
or TV pictures ...
> Personally I dont have a Problem with the FM IBOC, but time
> will tell. It has no place On AM
> Thats like placing a truck tire on a bicycle. Its a tire
> right?
> just on the wrong vehicle.. IBOC is the same thing just
> digital not rubber.
>
Update: Per this report titled:
AM IBOC DAB Laboratory and Field Testing
Paraphrasing ('cause the pdf cited above won't let me copy and paste):
"The IBOC codec encodes the audio digitally into 'core' and 'enhanced'
data streams and assigns those streams to different portions of the
spectrum. The core carries monaural data and the enhanced stream carries
enhanced fidelity and/or stereo ... the core data appears in the Primary
sidebands and the enhanced data appears in the secondary and tertiary
carriers ..."
Regards, _Jim
<P ID="edit"><FONT class="small">
Edited by _Jim on 06/05/05 01:16 AM.</FONT></P>
