Re: [IRCA] Fw: [Lowfer] Growling audio on MWBC signals

["Steve Ratzlaff" <steveratz@xxxxxxxxxxxx>]

There appear to be a number of stations using this low data rate signal. 850 
KOA +/- 16Hz; 1110 KFAB +/- 16Hz; 700 +/- 16 Hz. And some with either a + 
offset of +14 to +20 and some with a + offset and a different - offset -20 
to -14. Of course those might just be other stations off-frequency, hard to 
tell for sure. Info on the specs of this presumed low-data rate signal would 
be nice to read about.
Steve

----- Original Message ----- 
From: "Barry McLarnon" <bdm@xxxxxxxxxx>
To: "Mailing list for the International Radio Club of America" 
<irca@xxxxxxxxxxxxxxxx>
Sent: Wednesday, December 22, 2010 5:23 PM
Subject: Re: [IRCA] Fw: [Lowfer] Growling audio on MWBC signals


> On Wednesday 22 December 2010 17:51:27 scott@xxxxxxxxxx wrote:
> > > Something I hadn't known about Clear Channel stations, apparently they
> > > all have this....
> > > Steve
> >
> > I don't think they all do yet...or even many of them. I've yet to see any
> > gear installed for this at any of the stations I've visited.
>
> I wonder if the source of the "growling"has been mis-identified.  16 Hz,
> after all, is pretty much below the lower limit of the human audio 
> perception
> range.  Since the station in question (KSL) also runs IBOC, consider the
> possibility that this is actually the source of the noise.  The AM IBOC
> signal includes a pair of low frequency reference subcarriers (at +/- 182 
> Hz
> from the carrier) that are transmitted with a quadrature phase 
> relationship
> so that they don't produce any audible output (in theory, at least) from 
> an
> AM detector.  If you tune to the signal in SSB mode, however, this
> relationship becomes unbalanced, and you can hear a low-frequency rumbling
> sound along with the program audio.  Maybe this is the source of the
> "growling"?
>
> Barry
>
> --
> Barry McLarnon VE3JF  Ottawa, ON
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