[BC] IBOC power Increase For FM stations

[Mark Humphrey]

One question I raised (in my comments to the FCC on Docket 99-325)
concerns potential worsening of receiver-induced second-order intermod
between the digital sidebands of collocated FM stations with a 10.4 or
11.0 MHz separation.  If you examine the frequency relationship
between those sidebands, it's apparent that a receiver with
less-than-perfect front end might generate a broad noise product
centered quite close to 10.7 MHz.  This could result in the "sea of
carrier hiss" that Warren mentions.

Situations where Class B stations separated by 52 or 54 channels share
a common site are common in several major markets, including Chicago,
Washington, and New York.  Keep in mind that the proposed 10 dB
increase would raise each sideband's power to the equivalent of 2.5 kW
at 150 m, almost the same as a full Class A FM facility.  (Normally,
the FCC requires Class A stations with an IF relationship to be
separated at least 10 km.)

The single-station tests I've seen so far haven't addressed this
issue, but hopefully the NPR study will provide some useful data.

Mark

On Wed, Jul 15, 2009 at 8:29 PM, Warren Shulz<warren.shulz at citcomm.com> wrote:

>
> If I dial an analog radio with a RF signal strength meter the hiss of
> IBOC carriers cover the entire Chicago FM dial.  Going to 10% power will
> kill analog reception resulting in a sea of carrier hiss.    In Chicago
> few have the capability to go to 10% without yet another transmitter
> plant rebuild.