[BC] 8100xt2 pilot issue

[Broadcast List USER]

Most car radios just use signal strength to determine if the scan  
should stop on a station.  They don't use the audio level (though  
some scanner radios used by scanner hobbiests DO look at the  
modulation to avoid stopping on things that humans cannot  
"decode.").  Your car radio should stop scanning on any station, even  
if they have no audio on the air at the time (dead air).

HOWEVER, there are some car radios, and a few home stereos which also  
look for the presence of the pilot tone.  No pilot = no stop.

There have been some stations in the DC market over the years which  
have turned off the pilot to try to get a larger noise free listening  
area.  One suburban commercial station left the pilot off all the  
time; that is to say, they were a mono FM station.  They had an issue  
with radios skipping over them in scan and seek.  As I recall, they  
specifically called out Sherwood home receivers.

A DC public station had something like the early stereo TV stations  
used, but slightly different.  In the presence of L-R the station  
would switch to stereo.  When the L-R went away, there was a time  
delay after which the station reverted to mono.  The switch to mono  
was pretty pain free, but the switch to stereo could be very  
jarring.  As far as I know, both are in stereo now.

When C-SPAN bought what is now WCSP they announced they were going to  
double their power <!>, then explained that they would get twice the  
power by going mono <g>.  They were mono.  I have no idea if they are  
now, or not.  There really is no reason for them to ever be stereo.

I know a broadcast company that wanted to force receivers to blend  
early as they owned a lot of Class-A and suburban FMs.  They tried  
lowering the pilot injection to do this, and OF COURSE it didn't  
work.  They just needed to check the specs of the common receiver  
chips to figure this out.  Different radios fall out of stereo at  
different injection levels, but it seems that it generally falls  
somewhere between 3% and 6% of of 75 kHz deviation, not of total  
modulation (whether that be 70% or 120%).

The short answer is that if your pilot injection is low, your radio  
might skip your station.  Of course, if it is off frequency, that  
would cause problems too.

--chip

On Feb 11, 2009, at 6:01 AM, broadcast-request at radiolists.net wrote:

> Message: 8
> From: "Bowen, Jonathan" <jBowen at rejoice.org>
>
> This brings up a question I have been pondering. As far as I know  
> my 8100 is working fine. However that is the device that creates  
> the composite feed then ends up being transmitted after being sent  
> through my STL (usually except my stl died on me and I'm  
> downlinking satellite to it now) Anyway... I have noticed in the  
> past that when scanning on my car radio the radio tends to skip my  
> station. Could my 8100 be causing this by fluctuating slightly and  
> causing the pilot to shift just enough to confuse the radio?
>
> I haven't tried it after I bumped our audio level up a bit. We  
> where broadcasting softer audio and after I took over I bumped us  
> up a bit to make the level not loud but also comparable to other  
> radio stations. Could the lack of loudness be a more likely cause?
>
> Jonathan Bowen
> RBN Field Engineer