[BC] IBOC and the Law of Unintended Consquences

[Cowboy]

On Tuesday 19 July 2005 15:05, Tom Bosscher wrote:
>  I have a friend who just lit up a IBOC FM system. Since he had a new 
> digital/analog exciter, he had to set levels. Well, with the IBOC mask 
> on the air, the typical off air modulation monitor reads rather high, 
> seeing the digital subcarriers. He had to set mod at the tx site, 
> putting the mod monitor on the test port of the analog exciter.
> 
>  Then it was noticed that another newly "IBOC'd station in town,  is now 
> really loud on the analog side. Quite loud. You cannot take a look at it 
> with your standard monitor, as stated above. But you can tell it is not 
> aggressive processing, it is just that this station is running about 
> 125% mod.
> 
>  And guess what? It looks like you can get away with it. How is anyone 
> going to tell anyone what the analog modulation is, unless you are at 
> the tx site? 

 And, many thought I was nuts when I was opposed to that whole
 "transient response" thing that now makes it almost inpossible to accurately
 measure "legal" modulation as the FCC used to do, with an ultra linear
 detector, and a common O-scope !
 ( without IBOC, it's possible, but takes a storage scope )
 Most stations just used a mod monitor. Some, a spec an, but it's doubtful that
 a spec an is capable of accurately showing analog deviation in the presence
 of the digital carriers in the same spectrum, regardless of filtering.
 Is it a digital bit, or a transient peak ?
 Now, you have to measure the duration of the transient peak, and count how many
 per minute, AND know that it's not a bit, to know if it's "legally" over 150kc swing !

 An unintended consequence unintentionally complicated even further
 ( read $$$$$ ) by the addition of IBOC / HD ??

 I know, I know.
 I'm getting <sic> old, but I'm still working on crotchety !