The first Shoreview, MN tower with DTV coming off of it was the KMSP - channel 9 tower. KTCI DT16 was first and KMSP DT26 followed months after. Click on the photo to get a bigger image.
What do the signals "look" like?
Here is my portable test setup with a HP spectrum analyzer, 25db preamp, log periodic antenna for 300MHz - 1 GHz. For my readings, I put the antenna in a horizontal polarization. For this picture, I thought it looked better in a verticle polarization. (Truth isn't always beauty.) All readings were taken from about 5 miles west of downtown Minneapolis. Yes, you can see me and the camera lens in the screen shots. Please excuse that. This experiment was a quick diversion and not the main objective of my afternoon with the HP.
KTCI DT channel 16, horizontal antenna polarization. This looks similar to vestigial sideband (VSB) used in standard tv broadcasting. A pilot signal is visible as the spike on the left-hand side of the signal. Other than that, I see no discernible signals buried in it like with analog tv. This is the 8VSB digital tv standard.
More on the pilot signal... This is the location of the original AM carrier signal used to generate the modulated data you see in the 6 MHz bandwidth above. The AM carrier is filtered out (along with the lower sideband) and the pilot signal is added in it's place (at a much lower power level than the AM carrier would have been). I imagine this is done to conserve transmitter power, since an AM video carrier signal usually encompasses about 25% of power contained within the picture component of a broadcast tv signal - a waste of energy since it contains little information! The low amplitude of the pilot signal in the 8VSB signal shows that the ATSC was thinking clearly when they agreed upon the 8VSB standard. It is aparently very efficient with it's use of transmitter power!
For comparison, here is KCTI analog channel 17, horizontal antenna polarization. You can clearly see the AM video carrier signal at the left, the FM audio signal at the right and the color sub carrier in the middle right. Notice how the AM carrier is huge in comparison with the tv picture information, the FM audio and the color sub carrier. If you measured it, the video carrier would be about 25% of the power contained in this signal!
Also for comparison, here is KMSP analog channel 9, horizontal antenna polarization. Again, you can clearly see the AM video carrier signal at the left, the FM audio signal at the right and the color sub carrier in the middle right. FYI: With channel 9 being below the theoretical match frequency of the log periodic antenna, I should have changed to a biconical antenna to take an accurate reading. In the interest of time, I didn't bother.
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