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Most of the Voyagers' electronics are kept warm by electrical heaters powered by their RTG's, and presumably protected by some amount of insulation from the "cold of space" which means loss of heat via blackbody radiation. This is done because the carrier density in semiconductors (both intrinsic and those from dopants) is strongly temperature dependent.

See this answer for a short discussion of semiconductor dopant engineering for extreme temperatures.

On the ground, to improve signal to noise (S/N) ratio for weak signals received from deep space, dishes like some of the larger ones of the Deep Space Network use cooled front-ends. For more on that, see the cool images (pun intended) and links in Why doesn't thermal radio emission from a DSN “hot dish” completely swamp the benefits of a cold LNA?.

Terrestrially located RF front-ends need heavy, bulky refrigerators for cryogenic front ends, but in space, thermal radiation can potentially provide a simple cooling mechanism which would have become fairly isotropic as the spacecraft moved away from the Sun. Most of Voyager is really, really cold now. See answers to How cold are the Voyagers now? Colder than LOX? Colder than SOX?

I'm wondering if the first active device, the receiver's first amplifier stage or front end is colder than the main electronics box by design, taking advantage of the free cooling available in the outer solar system where it's needed most.

Question: Did any of Voyagers' receivers' front ends take advantage of the "cold of space" to lower noise?

"any of" is there because in addition to various receivers used for comms from Earth, there are antennas for other reasons as well, including possibly plasma experiments or microwave radiometric measurements.

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    $\begingroup$ Seems unlikely, the entire instrument box (which contains the receiver) is packed in MLI, temperature should be reasonably even within. $\endgroup$ – Hobbes Oct 10 '18 at 7:33
  • $\begingroup$ @Hobbes I'm thinking that there's a feed horn at the focus, coupled to a pickup in the waveguide connected to coax, and the coax is then routed to the receiver, and the thermal insulation of the coax is excellent so that the center conductor acts as a "cold finger" and cools the first transistor it touches. As you say though, probably not of course; I suppose that there's likely to be passives (inductor, capacitor) and a circuit board first. But still, there's always a possibility that the first stage front-end was in the feed horn with power DC-coupled to the coax. $\endgroup$ – uhoh Oct 10 '18 at 7:42
  • $\begingroup$ Line item 10) in Table 5-2 of DESCANSO IV - Voyager Telecommunications gives an operating temperature average of 59K for the uplink receiver which is tantalizing. (Downlink receiver is 3K which is consistent with the cryogenic systems on the ground). There may be something here. $\endgroup$ – uhoh Oct 10 '18 at 9:34
  • $\begingroup$ Instead, I've just asked Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K? $\endgroup$ – uhoh Jan 5 at 7:43

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