Re: iBiquity AM-band IBOC DAB

[Dan.Strassberg@att.net]

When you said that iBquity's AM-band IBOC DAB system 
uses only 15 kHz on each side of the carrier, you were 
wrong. I read the pertinent portion of the NRSC's 
report on the system. THERE ARE SUBCARRIERS at fc +/- 
15 kHz. The signal would be limited to fc +/- 15 kHz 
ONLY IF THERE WERE NO MODULATION! So, before you take 
me to task again, I suggest that YOU check YOUR facts. 
Whether or not the modulation extends to +/- 20 kHz, as 
I claimed (and I'd wager that it extends that far--and 
beyond), it certainly extends past +/- 15 kHz.

The NRSC report is a little frustrating to read, 
though. For the most part, the parts I read sound like 
a PR piece written by iBiquity's PR agency. The report 
does say that, contrary to my impression, the DAYTIME 
digital coverage is at least as good as the current AM 
coverage. However, I'd like confirmation of that from 
some tester that puts out research reports that don't 
read like PR pieces.

Whenever anyone puts out a document and bills it as a 
research report, he is putting his reputation on the 
line. Whatever the subject, a research report is 
supposed to be objective. There simply is no room for 
PR hype. If you find it, you are obliged to be 
skeptical at best--if not to discard the reported 
results out of hand.

In this case, one needs to ask the question of how the 
digital coverage was found to be as good as or better 
than the current analog coverage when most US AMs were 
built to the former protection rules and receive 0 dB 
first-adjacent protection at their 0.5 mV/m contours. 
The report states that you need some positive D/U ratio 
on the first-adjacent channel to receive an acceptable 
signal. If I recall, the ratio was not insignificant 
either (15 or 30 dB if I recall correctly). The 
requirement for a positive D/U is inconsistent with the 
claim of at least equal digital coverage.
--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367