Hybrid IBOC Parameters
The following technical parameters and spectrum details were gleaned
from the IBOC system specifications, which are now (as of April 16,
2005) a part of the NRSC-5 IBOC Digital Radio Broadcasting standard.
|No. of subcarriers per sideband
|Total subcarriers (both sidebands)
|Frequency spacing from carrier, kHz
|Modulation type (on each subcarrier of a
|Raw data rate, kb/s
rate (ratio of information bits to total bits)
|Data rate after error correction coding,
|Actual information throughput, kb/s
|Total power per sideband, dBc 
|Total power per sideband for 50 kW
station, Watts 
|Total power (both sidebands), dBc
power (both sidebands) for 50 kW station, Watts 
Primary IBOC Data Service, carrying station information, time of
reference subcarriers carry system control information such as mode and
power level (see note ).
||All lower/upper sideband
pairs except for the primary sidebands are complex conjugates (mirror
images) of each other and carry the same data, which cuts the overall
data rate for each pair in half. This is done to minimize
interference to an analog receiver tuned to the IBOC station.
||This is the throughput
available for the data payload after various housekeeping bits are
accounted for. The primary sidebands carry the core mode (mono) audio stream.
The data from the secondary and tertiary sidebands are combined
to carry the enhanced mode
stream, which provides stereo audio.
||The IBOC specifications
include a selectable power level control that allows setting the power
of the secondary, tertiary and PIDS sidebands to two different levels.
During the current interim operations, stations should be using
the lower power level, so the first of the numbers in entries having
two numbers should apply. Note that IBOC transmitters also allow
independent control of the primary sideband power level, which can be
used for mitigating adjacent channel interference, but this is not part of the IBOC
specifications. Power expressed in dBc is relative to the AM
Hybrid IBOC Power Spectrum
|Note: the IBOC specifications also include a mode that
allows the analog signal bandwidth to extend to ±8 kHz instead
of the usual ±5 kHz as shown above. There has never been
any test data submitted for this mode, and I seriously doubt whether
anyone will use it. There also has never been any test data
submitted for the mode in which the power of many of the subcarriers is
increased by 6 dB, as shown by the dashed lines in the digital spectrum
plot. If the FCC permits it, many stations will no doubt use it,
since it will increase the coverage for the enhanced (36 kb/s stereo)
audio service. The downside is that will noticeably increase the
noise level in most AM receivers tuned to the IBOC station.
© Barry McLarnon, 2005