Post Coital Bliss said:
Me and my buddies were wondering is anyone else seeing the 132% positive peaks on 101.9? I sort of remember the rules limited modulation to 110% if they were running subcarriers. What is the current rule regarding HD? Bob? Chief? Bueller?
Here's the deal....
Got a call years ago from Paul the GM of WTLC complaining WBKS (competitor) was overmodulating.
The gentleman was looking at the modulation on a receiver that was receiving no direct signal from the station.
As the FM signal (especially a class A) has a direct signal only in areas close to the transmitter site, the only good way to view it is AT the transmitter site.
The ideal and best way to check it is at the mod monitor port on the transmitter. This keeps outside signals out of the picture.
Monitoring near the transmitter on a dipole at 3 meters? Then the recommendation is to place a channel filter (cavity tuned to 101.9 bandpass) in between the antenna and receiver to filter out other services like paging, other stations, noise from other frequencies.
This is to ensure only the 101.9 signal is being verified for modulation and not anything that might be combining with it.
The biggest problem with checking ANY station is other buildings which reflect the direct signal and mix or combine with the actual signal.
At Emmis their air monitors are only accurate on Class B stations if the directional antenna is properly oriented.
That was pre IBOC. IBOC noise might make the reception worse.
Knowing the location of the 132% would be the first question.
That said, if they generate SCA they can legally generate 110% modulation.
110% and a reflected signal from ab uilding have the effect of 30 to 40 % modulation addition easily.
That said, 150% modulation is easily possible on current model exciters with no distortion. (That is if no distortion is on the encoded signal.)
I tried to call Jeff Goode and was told they were between engineers right now.
