007: 432MHz Peltier cooled Low Noise Amplifier for EME

 1987年虎ノ門会館でのEMEミーティングでJH1BRYの記念講演があり、その中でGaAs FETを少しでも冷却すればさらに低雑音になることを知った。電波天文台では液体窒素を使い冷却するが、アマチュアのシャックではそれは難しい。ならば半導体冷却ならどうだろうかと考え、ペルチェ素子を使い実験してみた。その結果一段で-30℃、二段カスケードにして-40℃を得ることができたのでこれを使って432MHz 用のプリアンプにまとめ、1989年の夏にNRAO (野辺山電波観測所)のJA0LB宮澤さんを訪ねてNF測定評価をお願いした。その結果、冷却により7K (NFにして0.1dB)雑音温度が下がることが確認できた。測定は何度も繰り返したが同じ値が再現したことを覚えている。この際に宮澤さんが作った70GHzなどのミリ波冷却アンプやmixerなどを詳しいデータとともに拝見でき、同行のJA0BZC,JA1AUHとともに有意義な時間を過ごすことができた。このプリアンプはその後アンテナに実装し、4.6dBのグラウンドノイズと10~11dBのサンノイズを観測したが、この時冷却有り無しでサンノイズの増加量は0.3dBであった。そして、この装置を使ってその年のARRL EMEコンペでは20局のエコーを捉えることができた。この実験試作の顛末はHJ誌 67号(1990年6月号P38~49)に掲載されている。

I participated in the 1987 JA-EME meeting at the Toranomon hall in Tokyo and got the memorial lecture of JH1BRY, and learnt to obtain more low noise if GaAs FET was cooled even a little. Usually, transistor is cooled by liquid nitrogen in the radio astronomy observatory. However, it is difficult for amateurs to do it in regular way. Then I bought and experimented on the peltier cooling device, because the semiconductor cooling was executable even by the amateur in the shack. The surface temperature reached -30℃ with a single module, and -42℃ was obtained with a stacked modules as an experimentation result. I made the preamp for 432MHz immediately using this. And then, I visited JA0LB/Mr. Miyazawa of NRAO (Nobeyama Radio Astronomy Observatory) and asked him for the NF measurement and evaluation in the summer of 1989. As a result, it was confirmed that 7K (0.1dB of NF) of noise temperature fell by cooling. I remember almost the same value reproducing it though he repeated the measurement several times. I was able to get 4.6dB of ground noise and 10-11dB of Sun noise when I mounted this preamp on the antenna afterwards. And, I observed more 0.3dB of the Sun noise when the Peltier was activated to cool the GaAs FET. The echo of 20 stations was able to be caught in the ARRL EME competition of the year with this cooled LNA. This passage was published in No.67 of the Ham Journal magazine (P38-49 at the June 1990 issue). I was able to enjoy this attempt enough. However, the NF reduction effect was not able to be said enough by practical use EME equipment viewpoint. Perhaps, if the Sun noise increased by 1dB or more, I think that the self-evaluation changed. Making was in 1989.



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