Re: [IRCA] Fw: [Lowfer] Growling audio on MWBC signals (1160 KSL)

["Steve Ratzlaff" <steveratz@xxxxxxxxxxxx>]

I'm probably 400+ miles from Salt Lake City, Utah but 1160 KSL is a good 
signal here presently (an hour or more after sunset), and on Perseus SDR in 
CW mode, 8 Hz bandwidth, zoom, I'm easily seeing +/- 16 Hz sidebands 
relative to 1160.000. The strongest carrier signal (1160.000) is assumed to 
be KSL, which fits with its IBOC-accurate carrier. In AM mode KSL is what 
I'm hearing for the dominant station.
(I'm also seeing a +35 Hz fairly strong signal which I assume is some 
non-IBOC station, quite aways off frequency; as well as a -11 Hz weak 
signal.)
73,
Steve
NE Oregon

----- 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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