在1960年代的960 MHz射電望遠鏡中會出現什麼"晶體混合器"?


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在對 this answer的評論中引用的論文中,在1950年代,具有便攜式天線的射電天體位置如何如此精確,可以將其分配給昏暗的光學對等物(類星體)?

1963年的論文是Accurate Measurement of the Declinations of Radio Sources(單擊小的PDF圖標),並且在下面引用了包含短語"晶體混合器"的兩個摘錄以及框圖。

當我聽到"晶體"時,我想到的是振盪器的石英晶體,或者帶有氧化物表面的金屬晶體(例如方鉛礦),用於使用cat's whisker contacts來製造二極管,但是對於混頻器中的二極管檢測,真空管和固態半導體二極管存在於1960年代,儘管我不知道960 MHz下的性能。

問題:在1960年代的960 MHz射電望遠鏡中,什麼是"晶體混合器"?


由兩個相距200、400或1600英尺,工作頻率為960 MHz的射電望遠鏡製成的天文干涉儀的框圖。每個盤子正下方顯示有問題的攪拌器:

Fig. 1.—Block diagram of the receiver (Owens Valley radio telescope interferometer circa 1960's

"晶體混合器"在紙張中出現兩次;在第2頁上:

The arrangement of the components of the receiving equipment is shown by the block diagram of Figure 1. The receivers were of the superheterodyne type, and the crystal mixers were connected by short lengths of cable to the antenna feeds without any pre- amplification at the signal frequency. The local oscillator frequency was 960 Mc/s, and the center frequency of the IF amplifiers was 10 Mc/s, with a band width of about 4 Mc/s. No attempt was made to reject the image response of the superheterodyne. Note that the IF amplifiers were split into two sections. The IF preamplifier was located at the prime focus of the paraboloid along with the mixer and amplified the signal sufficiently to allow it to be fed through a long connecting cable to the remainder of the receiver, which was located in the laboratory building.

並再次在第3頁:

The local oscillator power for each half of the receiver was supplied by a separate klystron oscillator, which was phase-locked by a closed-loop servo system to reference signals of a common, central origin. The high-frequency refer- ence signal power required by the system for a satisfactory lock was about six orders of magnitude weaker than the available local oscillator power required by the crystal mixers of the superheterodyne receivers. The problem of getting phased local oscillator power to the two antennas when they were being used at large separations was thus greatly simplified.

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No attempt was made to reject the image response of the superheterodyne.

This suggests that the designers wanted nothing to phase-shift RF signals...important in an interferometer - everything between antenna feed and the 10 MHz I.F. amplifier would be quite broad-band. And gain (actually loss) of diode mixers is fairly well-controlled.
Keeping those two RF paths identical was likely an important design goal. Perhaps their signal source was a strong one so that receiver sensitivity was not a limiting factor.

Have a 1960-era VHF mobile phone that used a single point-contact germanium diode mixer very much like this, very first stage of the receiver. However, tuned circuits were placed between antenna and mixer to reject the image response. Many TV tuners of that era used a similar approach.
Diode mixers work nicely at very high frequency - generating the local oscillator power to drive them is the bigger problem.