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Re: Frequency Sweeps? What? Who?

Posted: Wed Jan 18, 2017 5:00 am
by NK7Z
I manage the Dopplergrams group on Yahoo, Peter also lives there, he is a bottomless put of information... The man is amazing.

Re: Frequency Sweeps? What? Who?

Posted: Sun Jan 22, 2017 2:30 am
by bubblegumpi
I always have a hard time figuring out whether these signals are manmade or natural, and more importantly if they are even real in the first place; there are ALOT of phantom signals that live inside my SDR. I.E. the sweep that goes up, if you tune down at the same rate, your tuning down, you can only hear the signal by clicking the mouse directly on them. You can never scroll tune to it because the signal always moves opposite. Or there's the pesky peak that is always in the same spot on the waterfall screen no matter how you tune (goes away on restart, so a software based signal rather then a real harmonic inside the SDR?). A better understanding of these internal signals and why they are there would help. (Anyone know a link that explains?).

I figured those long ones (that are in your pic) were lightning strikes or other natural phenomenon, because they seem kind of like whistlers. Those are man made?

What about the "Zebra" stripe (sounds like woosh woosh woosh on any modulation) ones that are constantly found in the 3-10MHz range and are exactly(?) 0.5MHz in width. They always sweep down too. I always figured they were some type of inductive load noise like a machine, but we don't have much industry around where I live, so I don't know. Those are intentional?

Re: Frequency Sweeps? What? Who?

Posted: Sun Jan 22, 2017 10:45 am
by 13dka
bubblegumpi wrote:
What about the "Zebra" stripe (sounds like woosh woosh woosh on any modulation) ones that are constantly found in the 3-10MHz range and are exactly(?) 0.5MHz in width. They always sweep down too. I always figured they were some type of inductive load noise like a machine, but we don't have much industry around where I live, so I don't know. Those are intentional?


That sounds like you mean CODARs, you can find those and many other signals explained here: http://www.sigidwiki.com/wiki/Signal_Id ... tion_Guide

Re: Frequency Sweeps? What? Who?

Posted: Thu Jan 26, 2017 9:46 pm
by NoelC
I have a background in data comms, having worked on modems and such things in their heyday.

I've imagined that the wide, smooth "whoosh whoosh" signals are some kind of digital signal with phase modulation. That they look like rope is I think a product of propagation quirks.

And yes, I do use that wiki site quite frequently.

Some tips I've learned for maybe making the SDRuno display a bit more real (less phantoms):

1. Don't turn the gain up too much. The AGC feature usually chooses well. If it turns things down, there's a reason.
2. In the main configuration, choose Low IF instead of Zero IF. That eliminates that central "phantom signal".

-Noel