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Table 1 of this document gives Spacecraft Transponder Turnaround Ratios that are supported by the Deep Space Network. These are the PLL controlled divide-by ratios that a spacecraft uses when receiving a carrier frequency from the DSN and retransmitting a different frequency back to Earth which is still phase-coherent, for the purposes of precise doppler shift measurements as part of a determination of a (usually deep space) spacecraft's trajectory. Read more about this in this question.

Some of the supported ratios are within-band and close to unity; X to X-band, Ka to Ka-band and S to S-band. This means that the spacecraft must simultaneously receive a very weak signal and transmit a very strong signal at frequencies that are very close, and this requires more frequency rejection in the spacecraft's receive circuit.

Question: Are there any deep-space spacecraft which actually support within-band turn-around for Earth-based doppler measurements? Are these spacecraft using one dish for simultaneous receive and transmit within the same band?

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Yes, and yes. The standard Doppler data type on deep-space spacecraft is X-band to X-band, and transmit and receive are on the same antenna. Most deep-space spacecraft only have X-band transceivers. A few have more than one band, usually for either radio science reasons and/or higher data rate on Ka (accepting some added risk of weather interference). S-band is passé.

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  • $\begingroup$ A quick check of a few spacecraft confirms this - thanks! $\endgroup$ – uhoh Oct 12 '17 at 1:35

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