Doug Smith W9WI wrote:

On Wed, 23 Jan 2008 14:52:57 -0800, tom k in L.A. wrote:

Please enlighten me: Why is IBOC so Evil?

The primary complaint is that the IBOC digital signal is transmitted in
two channels either side of the station using it, causing massive
interference.

For example, if a station on 1510kHz runs IBOC, the digital signals are
transmitted in 1495-1505kHz (interfering with stations on 1490 and 1500)
and from 1515-1525kHz. (interfering with 1520 and 1530kHz)

That can be compared to an analog station on 1510. Its transmissions cover
from 1500-1520 kHz. This interferes with the stations on 1500 and 1520.
Adjacent channel interference is managed by keeping station apart both
geographically and frequency-wise. This may work during the day, but not at
night.


(on FM, only one frequency on each side is interfered with, and in many
cases those frequencies were already useless due to interference problems
involving the station's *analog* signal. It does make things hard on
FM DXers though.)

Other complaints:

- Poor coverage in the current "hybrid mode", where analog simulcasts must
be accomodated.

Poor coverage of the digital portion, the analog portion of the hybrid
signal still has the same coverage.


- Self-interference: if the station isn't balanced properly or the
receiver has an unusually wide IF bandwidth, the IBOC digital signal can
interfere with the station's own analog signal.

Yes, the higher fidelity receivers suffer more with than cheaper ones
because of the digital signals.


- We could have had something better. A system called "Eureka-147" is
seeing success in Britain and at least in technical terms across Europe.
This Eureka system would have offered improved fidelity over IBOC, more
subchannels, and no interference issues.

However, the FCC required a digital system to be compatible with analog.
Eureka-147 is not used in the AM band. This is not without issues, though.
Switching encoding from MPEG to AAC+ will obsolete many receivers.

An interesting note, the AM analog signals received on my IBOC receiver
sound better than that heard on almost any other AM receiver I own. The FM
on the receiver appears to have excellent selectivity also.

For me, FM IBOC works. The IBOC signals are clearer. The second program
offerred by some station does provide unique programming.

For me, AM IBOC is a waste. I can receive no AM digital transmissions. I do
hear the interference caused by the digital signals. (I am also 50 miles
from the nearest transmitter using IBOC.)

The FCC is managing the airwaves in a manner that does not support DXing.
They are focused on radio working in the local markets, not long distance
reception. The broadcasters are also focused on the local markets as that
is where the advertising revenue comes from. On AM, IBOC is attempting to
improve audio fidelity for listeners in the local markets. It may (or may
not) be working.

craigm