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Old 13-Sep-2020, 7:53 PM   #52
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,677
Quote:
Originally Posted by tripelo View Post

Curious about scale accuracy, sorta related to scale linearity:

Is a dB indicated, an actual dB.
The only dB scale on an SDR that I have confidence in is the dBm calibrated scale for the RSP1a with SDRuno software. I used it during the above test.









I couldn't figure out a way to get a direct reading of the signal power as shown in the YouTube video or with my NTSC modulator, so I had to settle for using a correction factor. It's probably measurement-bandwidth related.

Correction factor
99.5 - 85 = 14.5
-70.1 dBm + 14.5 = -55.6 dBm

Regarding linearity:
The signal does appear to be about 30 dB weaker at dropout on the calibrated dBm scale AND the relative dB scale.

With a flat signal, the placement of the measurement window isn't very critical, but with a signal that doesn't have a flat top, it's up to you to place it at an average level point.

This is the way my signal level meter does it, and takes the average:

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Last edited by rabbit73; 14-Sep-2020 at 2:03 AM.
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