Observation 3063643: How to read the waterfall frequency

Regarding Observation 3063643

In the middle of this observation is an announcement for a repeater that I believe is located 1350 kilometers from my station. I believe the repeater frequency is 145.485 but I’m not sure if I’m reading the waterfall correctly. Could someone please confirm and explain? Thanks.

Hello @FredricRaab I would say it might be around 145.475 and not 485. My reasoning is this:
The waterfall you see (and the observation as a whole) is doppler compensated.

This means that the scheduled frequency is only exact at the Time of Closest Approach (TCA) which in your case is the middle of the observation period.
Thus as you move back or forth in time you cannot really use the x-axis (frequency) scale on the bottom of the WF to calculate a frequency.

That said, since we know the doppler compensation mechanism, as we move forward in time in this case we lower the observable tuning frequency. That would make the terrestrial signals appear higher in freq, and since the repeater signal is after the TCA I would deduce that it is probably around 145.475 in reality.

Soon we will have a new waterfall format that will allow us to do analysis in place (with markings, doppler plots etc) and will make such explanations easier to follow :slight_smile: .