locked Re: Unfamiliar signals in waterfall #FT8 #Waterfall

Bill Somerville

On 12/02/2021 05:51, Kenneth Williams wrote:
I was wondering if anyone had a comment on what I might be looking at or what might be happening to result in this waterfall display.
Also, if you look at the graph at the bottom, it also looks strange, but consistent with the waterfall in terms of cumulative power vs fq.

This is from v2.4.0-rc1 on a 64-bit windows 7 machine operating FT8.

I don't think I've ever seen anything like this.

Thanks in advance for any comments or thoughts.

Hi Ken,

at first glance those look like typical audio harmonics generated by stations over-driving their transmitters modulator audio input. There are two particularly bad examples there. Note they could be generated at your end, and in this case I think that may be the case as every signal above a certain strength seems to be distorted. Make sure you do not have excess RF GAIN, e.g. if you have the AGC off then reduce the RF GAIN until your Rx audio is linear again. Also make sure your NB is disabled, they can cause distortion when there are strong signals in the Rx passband.

You can easily verify if the problem is at your end, simply tune your rig's Rx off by 500 Hz and see if the harmonic relationships change or just shift in frequency by the amount you shift frequency. A shift implies the problem is at the transmitting station, whereas if the harmonic spacings remain relative to your base frequency (signal offset times 2, times 3, time 4 etc.) then the problem is at your end.


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