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Measuring modulation

192khz:

As Kelly A said, your measuring device should set for the center frequency of the station you are measuring.

btw- FM station modulation is usually expressed as percentage modulation, which is a measurement of RF carrier frequency deviation under modulation. Plus and minus 75 kHz deviation (from center frequency) is designated as 100 percent modulation, which in turn is a peak audio level after demodulation by a receiver. A very well-known peak level indeed :)

Bandwidth is the total RF spectrum occupied by the signal. Of course, this is affected by modulation.

Bandwidth of an FM modulated RF carrier is said to be infinite. More practically, occupied bandwidth is considered the bandwidth in which a high percentage of the radiated power is contained. FCC determined that with plus and minus 75 kHz deviation enough of the signal would be contained within a 200 kHz bandwidth, that it would be reasonable to establish 200 kHz spacing between FM channels.
Thus, in the case of typical FM, deviation is 75 kHz and occupied bandwidth is considered to fit acceptably in the 200 kHz channel.

192khz why are you interested in modulation? Is it because you hear differences in loudness between radio stations?
 
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Greg Strickland said:
192khz:

As Kelly A said, your measuring device should set for the center frequency of the station you are measuring.

btw- FM station modulation is usually expressed as percentage modulation, which is a measurement of RF carrier frequency deviation under modulation. Plus and minus 75 kHz deviation (from center frequency) is designated as 100 percent modulation, which in turn is a peak audio level after demodulation by a receiver. A very well-known peak level indeed :)

Bandwidth is the total RF spectrum occupied by the signal. Of course, this is affected by modulation.

Bandwidth of an FM modulated RF carrier is said to be infinite. More practically, occupied bandwidth is considered the bandwidth in which a high percentage of the radiated power is contained. FCC determined that with plus and minus 75 kHz deviation enough of the signal would be contained within a 200 kHz bandwidth, that it would be reasonable to establish 200 kHz spacing between FM channels.
Thus, in the case of typical FM, deviation is 75 kHz and occupied bandwidth is considered to fit acceptably in the 200 kHz channel.

192khz why are you interested in modulation? Is it because you hear differences in loudness between radio stations?
Click to expand...
Yeah I know in stereo tool there’s a frequency to modulate a test tone. Like what test tone is adequate to measure fm mod?
 
192khz said:
Yeah I know in stereo tool there’s a frequency to modulate a test tone. Like what test tone is adequate to measure fm mod?
Click to expand...
A tone at one frequency can be used to set levels. But for audio, you want to test a range of frequencies, from below 100Hz up to 15 kHz. That will test both levels and frequency response of the system if the objective is to be as close to flat as possible over the audible range.
 
192khz said:
Yeah I know in stereo tool there’s a frequency to modulate a test tone. Like what test tone is adequate to measure fm mod?
Click to expand...

192khz your words are not making sense. What are you seeking to know? Do you have an audio processor and a transmitter, and you would like to set modulation? I'd say if it is a Part 15 FM transmitter, don't stress, just set modulation so loudness is about the same as other stations, when your audio processor is adjusted to sound similar to the other stations.

Are you adjusting processing and modulation on a licensed FM broadcast station? These days many low power transmitters for licensed stations have modulation peak meters built in, and/or have an audio processor built in. That is fine to get you in the ballpark.

Have fun, and keep on thinking about audio and modulation, my friend.
 
Greg Strickland said:
192khz your words are not making sense. What are you seeking to know? Do you have an audio processor and a transmitter, and you would like to set modulation? I'd say if it is a Part 15 FM transmitter, don't stress, just set modulation so loudness is about the same as other stations, when your audio processor is adjusted to sound similar to the other stations.

Are you adjusting processing and modulation on a licensed FM broadcast station? These days many low power transmitters for licensed stations have modulation peak meters built in, and/or have an audio processor built in. That is fine to get you in the ballpark.

Have fun, and keep on thinking about audio and modulation, my friend.
Click to expand...
Okay if it’s one of those car fm transmitters it’s all good? It’s possible to give it mpx if you feed it a mono signal.
 
I'd say if the car FM transmitter has a stereo audio input (left and right channels) and it broadcasts that stereo audio successfully to a car radio receiver, you cannot feed composite MPX into it. You could feed processed stereo audio into it and see how it sounds on the car radio.

Now let me get this straight- you want to run a software audio processor on the music you are feeding into a car radio transmitter and listen to it on the car radio? If so, you are bitten by the bug, and you need to find a licensed radio station that will let you hang out, be an intern or work there.
 
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Greg Strickland said:
I'd say if the car FM transmitter has a stereo audio input (left and right channels) and it broadcasts that stereo audio successfully to a car radio receiver, you cannot feed composite MPX into it. You could feed processed stereo audio into it and see how it sounds on the car radio.

Now let me get this straight- you want to run a software audio processor on the music you are feeding into a car radio transmitter and listen to it on the car radio? If so, you are bitten by the bug, and you need to find a licensed radio station that will let you hang out, be an intern or work there.
Click to expand...
There are a lot of stations that need engineers
 
Digging way back in the old memory bank but I remember something about Belar FM mod monitors. You would drive the audio with a certain frequency and then use Bezel functions to calibrate it. Ring a bell with any one?
 
Kelly A said:
But unfortunately there aren't a lot of companies who allow interns to work in the engineering department. Too much potential safety and associated liability concerns.
Click to expand...
Famous last words... "what's this thing do?"

(The "zap" always precedes the "don't touch that!")
 
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