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This tweet by deep space SDR enthusiast and amateur radio operator Edgar Kaiser @df2mz shows a squiggly tone from MRO.

Mars Reconnaiscance Orbiter (MRO) X-band downlink. The signal shows this kinky behavior due to a specific uplink protocol keeping the uplink signal frequency within the optimum bandpass of the spacecraft's coherent transponder. Distance was 193 million km.

Question: I would like to understand the details of shape of this frequency versus time plot of received signals from MRO.

It runs about 13 minutes long and shows a general quadratic behavior with some superimposed stepping. Is there a name for this, or documentation? How does this relate specifically to MRO's orbit?

CLICK for full size:

enter image description here

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  • $\begingroup$ The overall slight increase of frequency is just Doppler effect as both sender and receiver are accelerating. The wiggly structure can't be seen in any of the recordings that uhf-satcom did: twitter.com/search?q=%40uhf_satcom%20mro&src=typd Maybe a slight hint of them in some. $\endgroup$
    – asdfex
    Jan 19, 2019 at 11:11
  • $\begingroup$ @asdfex I'm particularly interested in "understand(ing) the details of shape" of this "just a doppler effect" as well as the wiggles. $\endgroup$
    – uhoh
    Jan 19, 2019 at 13:50

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