Noise Burst?

I see these bursts of noise from time to time on 40 meters. I have expanded the spectrum display and it is fairly broad band but it varies in amplitude across the spectrum. It doesn’t look like typical noise and sometimes I wonder if it is a sampling Phenomenon in the SDR as a reaction to a noise input. Has anyone else seen this. Today when I saw it I logged into my buddies system, a Flex 6700 in North Carolina to see if it was wide spread. Didn’t see it at all on his Flex. I have uploaded a short video from my phone camera.

Does anyone have an idea what this might be?

2 Comments so far

  1. SiliconGraybeard on February 8th, 2017

    I don’t have a Flex, but it does look like an overload thing. There’s a big signal on the right end of the screen. Swag at -15 dBFS. The jumps in noise floor seem to coincide with the CW characters. Two signals at -15 dBFS only add to -12 (-9 on peaks), so there would have to be more big signals off screen, but still in the ADC’s input.

    If the total power reaching the ADC exceeds full scale, I could imagine something like that happening. I think I recall seeing something like it once or twice in the Collins HF during development.

    I wouldn’t let software completely off the hook either. The fact that your friend’s system doesn’t do it could just mean he doesn’t have the other big signals going on.

  2. N4RFC on November 15th, 2017

    This was caused by turning on the “Weighted Average” on the Display. Apparently that function is geared toward very weak signals and where there are strong signals in the passband of the ADC it will cause the display to wank up. Turning off Weighted Averaging cures the problem.