Quote:
|
Originally Posted by verder
It's not much, but one experiment I performed has been to find the pilot frequency for each channel using my Airspy R2 + SDR#. The Airspy has a wide enough bandwidth so I can see the "whole" signal at once. I used this to see what gain setpoints I needed to place that pilot frequency peak at -40dB to -45dB. The Airspy gain setpoints ranged from 3 to 13:
KFME: 6
KVRR: 7
WDAY: 3
KRDK: 8
K28MA: 13
KXJB: 8
KVLY: 10
I realize this doesn't show any sort of bit error info or whether I've got multipath issues going on, but I'm at least able to "see" things.
Thanks for help so far and relaying my posts to the thread!!!
|
Using the pilot is certainly helpful in finding a channel, but the strength of the pilot is not a reliable measurement for the strength of the channel. Multipath reflections can affect the strength of the pilot without making a comparable change in the strength of the channel.
Analog TV signals use a peak measurement of the video carrier, but the strength (actually power) of a digital TV channel is the average power across the whole channel.
If you look at your scan, you might be able to see that there isn't always a good correlation between the average power of the channel and the strength of its pilot, like KXJB vs KVLY, or KVRR vs KRDK.
I think a better indicator of the signal quality of a channel is the SNR of the channel implied by the scan when the gain of the of SDR# or Spectrum Spy software is properly adjusted for max SNR. Bring the gain up to the point just before the adjacent noise floor starts to rise.
Video of adjusting gain for CH 31
I should have shown some of waterfall so that the freq scale would show
https://www.dropbox.com/s/hzmz4mvte4...50-57.mp4?dl=0
https://www.dropbox.com/s/hzmz4mvte4...50-57.mp4?dl=1
CH 16
https://www.dropbox.com/s/0jlgno1gtj...02-31.mp4?dl=0
https://www.dropbox.com/s/0jlgno1gtj...02-31.mp4?dl=1
The difference between the adjacent noise floor and the average level of the top of the signal that you see on the screen is a fairly good estimate of the SNR. However, it might not be exactly the same as the SNR given by the TV diagnostics menu. It would be difficult for the TV to measure the level of the noise floor when the channel is in use. What the TV is giving is actually the MER (Modulation Error Ratio) which is derived from the constellation diagram. The MER includes the affects of impediments like multipath errors.
https://blog.solidsignal.com/tutoria...h-snr-ber-mer/