[BC] IBUZ on another station daytime

[Phil Alexander]

On 31 Oct 2005 at 17:20, DHultsman5 at aol.com wrote:

> While driving between Portland, Maine and Scranton, PA last Saturday I was  
> NW of Boston on I-495 I was listening to a station with the "Legends" format on 
>  1490 and as I drove around a noise came up on the music programming.  It  
> was the background "I-buzz" right under the music.  No splatter just  noise.  It 
> so happend that there was a talk station that was running HD  Radio on 1470 
> kHz.  the HD noise interferred with the music.   I  may have the frequencies 
> mixed up  it may have been 1450 and 1420  kHz.  anyway  it wasn't the normal 
> over modulation sideband splatter  it was the actual noise below the music.   
> This is the first time I  have heard what it may do to local nearby channels. I 
> was listening on a factory  radio in a new Ford Taurus.

This is very predictable in cases where a first adjacent DA is an IBOC
emitter and the desired signal is an analog located in one of the DA's 
nulls. Without extensive transmission system rework - IOW whole new 
system between Tx and towers - there is sure to be a first adjacent 
problem in a DA's nulls.

This is where the VSB mode of DRM would alleviate many problems by
putting the digital only on the side away from the critical adjacent,
and allowing array tuning over a narrower phase b/w.

Second adjacent may be more a function of receiver selectivity and/or 
IBOC Tx IMD.

Until dynamic predistortion becomes a standard feature on AM IBOC, we
will probably see second adjacent problems, and IMHO, even with PD it
is a good idea to have constant monitoring of the Tx output for 
compliance.

>   I have heard the noise while in Atlanta listening last winter to  WLAC 
> Nashville on 1510 with the noise interference on channel from the WSAI  1530, 
> Cincinatti until they turned off at 6PM EST.
>  
> There has to be some way to have this noise cancel out on adjacent channels  
> using DSP's in the receivers or something????

Since it is the reaction of an analog detector when presented with digital
signal, sadly, the answer is probably not.


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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