Wacky Waving Inflatable Arm-Flailing Carrier!
Wacky Waving Inflatable Arm-Flailing Carrier!

A bit more about the testing yesterday. What you see in this video before the 2 minute mark is a plain FM Stereo Carrier. In this case it is the carrier for 103.1, which was broadcasting out of Hendersonville. With no audio being fed to the transmitter, you should see these 5 points. They should not move. But they do occasionally with this transmitter, it wants to dance at times. To a listener this could sound like you were jogging the tuning knob back and forth over a station. Needless to say, this is an issue.

The top segment of the screen in the video shows the frequency on the horizontal axis, and amplitude (signal strength) on the vertical. The lower left just shows a close up of the highlighted grey section. Just under the top segment is what is called a waterfall display. It is displaying the same information as the top segment, but now adds time as another measure. Amplitude is indicated by color. Then finally in the lower right section we have a breakdown of the audio that the receiver is demodulating. For the first 2 minutes, we were feeding no audio, from 2- 4 ish min we are feeding a 7.5kHz tone, and you can see the spike indicating that.

 

Update:

While a carrier shift of this intensity and length is an issue, I need to correct myself on one point.  It would be normal to see a short duration set of carrier shifts once an hour.  Once an hour each translator IDs itself per FCC requirement.  It does this by encoding its ID using Morse Code and briefly shifting the carrier frequency to express this.