Re: NRSC and AM-IBOC

[dan.strassberg@att.net]

I got the 40-kHz number from the iBiquity Web site, 
shortly after the company was formed through the merger 
of USA Digital Radio and Lucent Digital Radio. That was 
a couple of years ago. Perhaps the 40-kHz number has 
since been reduced to 30 kHz. I haven't checked. But 
even at 30 kHz, the sidebands of stations such as WEEI 
and WCRN will overlap substantially within the stations' 
daytime 5 mV/m contours, which means that these stations 
will cause objectionable interference to each other. 
There appear to be further examples, just in the Boston 
area, of AM stations that, if their sidebands contain 
more than nominal amounts of energy 15 kHz from the 
carrier, will cause interference within second- and 
probably third-adjacent-channel stations' currently 
protected contours.

In addition, about a year ago, a friend who lives in 
Montgomery County MD, outside of Washington DC, reported 
on the interference over an area of the AM band that 
extended from at least 860 to 940 kHz (80 kHz) and was 
apparently caused by a station on 900 that was testing 
the iBiquity system.

It hasn't been all that many years since the FCC 
increased the first-adjacent protections on the AM band 
from 0 dB to 6 dB at the so-called interference-free 
contour, but the huge number of stations that became in 
violation as a result of this rule change were not 
required to modify their operations to eliminate the 
overlap unless they made some other modification. At the 
time of the rule change, the second-adjacent-overlap 
criteria were relaxed. It was this latter change that 
paved the way for WCRN's daytime power increase to 50 kw.

My contention is that any system that causes more 
sideband energy than is currently permitted by the NRSC 
AM channel mask will require large numbers of existing 
AM stations to either go dark or to accept heretofore 
impermissible levels of adjacent-channel interference. 
That is my definition of an unworkable system.

I believe that I am entirely within my rights to express 
my opinion on whether a modulation system proposed for 
use on the public airwaves is workable. After all, 
anyone who owns a radio--which means essentially 
everyone in the US--will be affected if our broadcast 
technology is changed--especially if the change causes 
people to spend substantial sums on new receivers based 
on a technology that turns out not to work acceptably.
--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367
 
> Hey Dan, got any evidence to back up those claims?  I'm sure iBiquity & 
> NRSC have time for a libel lawsuit.  The NRSC's EXACT words were:
>