Why is the operating temperature for the Voyagers' receiver noise calculation about 1550K?

In line 10 of Table 5.2 of DESCANSO IV - Voyager Telecommunications it shows a value of the uplink receiver noise spectral density of -166.7 dBm/Hz, which is 196.7 dBW/Hz which is 2.1E-20 Watts/Hz = $$k_B T$$. With $$k_B$$ = 1.381E-23 J/K that's a temperature of about 1500 K (which seems really hot!) and that agrees with the stated operating temperature of 1545K which again, seems really hot!

In Table 5.3 for the downlink receiver at DSN, the noise temperature is 21K and that's consistent with it being cooled to about 13K. But I can't understand this 1500K figure for Voyager, it seems unphysical unless the technology is so old that the source of the noise is the 1970's era front-end transistor itself.

Were they really that noisy back then?

• Was this based on a worse case environment close to Jupiter, perhaps? – Steve Linton Jan 5 at 10:55
• @SteveLinton Same line 10 in Table 5.3 shows a detailed breakdown for contributions, including Ground, Galactic, and Atmospheric. You may be right but if so, I'd be surprised they defined the Operating Temperature to be ~1500K rather than break it down as received noise. My hunch is that this is partly related to why home satellite dishes used to be so big; old transistors were noisy. – uhoh Jan 5 at 11:06
• You may well be right, but I was thinking of the effect of particle strikes on the receiver/amplifier, rather than incoming radio noise. Don't know if that would be classified the same way, – Steve Linton Jan 5 at 12:25
• @SteveLinton thats interesting thinking! – uhoh Jan 5 at 12:34