[BC] Blending issue

[Jeff Welton]

Barry commented:

> There has been some recent discussion about a phase problem with the
> audio when IBOC receivers "blend" to analog.
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> Apparently there are cases where the analog and the "decoded digital"
> are out of phase to each other, and the radio goes "quiet" for a
> moment.  Some have attributed this to a recent software upgrade on
> some IBOC exciters.
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> Another person told me this week that this issue has been known for
> some time, and pointed to a specific processor.   I won't name it
> here, because I am not in position yet to verify that.
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> However, it may be useful for anyone running IBOC to verify the blend
> is without "dropout."

Barry - if I was the person to whom you're referring, I misled you =
(sorry!).  I'm going to plead that I didn't completely understand the =
question over the phone (bad Jeff, go to corner, write, "understand, =
then respond" 100 times).

While I haven't really been following the topic, the above sounds like =
primarily an issue of synchronization.  Folks, it is CRITICAL that you =
synchronize the analog and digital audio signals - even if (in the case =
of FM) the analog audio does not go through the HD generator.  In the =
case of FM, not synchronizing the audio can definitely cause dropouts =
when blending between analog and digital.  In AM, lack of synch will =
also cause dropouts and can, on occasion, cause the HD generator to lock =
up if the two signals meander far enough out of phase.  Our NE-IBOC =
generators (I assume the rest, but don't know for sure) have a couple of =
ways with which you can synch the audio.  First, there's a sample rate =
converter provided in the auxiliary unit that is part of the NE-IBOC =
package.  This can be connected to the output of the STL (or whatever =
receives the program audio at the transmitter site) and used to drive =
both the analog and digital processors.  Alternately, the NE-IBOC main =
unit has three 10MHz clock outputs which can be used to synchronize =
external devices, or one of the sample rate converter outputs could also =
be used to synchronize the processors, if the processor has the ability =
to synch to an external input.  There are other options, don't hesitate =
to call your manufacturer for additional information

> ... that is ... IF you have a receiver.  Amazingly, I still hear of
> stations installing digital without even having one receiver on hand.

I've been to a few where the only digital receiver was in the GM's car - =
not available at installation time - or in the regional DOE's car - also =
not available.  I've only installed two that I can think of where we =
actually had a receiver done up so that we could listen in the site to =
what we were putting on the air.

Just some thoughts from the rainy, foggy North East (I'm not =
complaining, a customer in Tennessee just told me it was 20 degrees =
there (near Knoxville) this morning - the lowest temperature we've seen =
so far recently has been about 40).

Best,

Jeff Welton
Customer Service Dept.
Nautel Limited
Tel: +1-902-823-3900, ext. 127
Fax: +1-902-823-3183
jwelton at nautel.com=20


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