006: 1296MHz scalar feed horn (VE4MA)

 VE4MAがこのホーンフィードと直径9フィートのディッシュで1296や2304MHzのEMEに活躍していると知り、マネしてみるつもりで先ずはフィードだけ作ってみた。単なる円形導波管(いわゆるCoffee Can)ではリムへの漏れ電流が大きいため、放射パターンが崩れてしまうからアンテナ雑音温度も高くなってしまう。このVE4MAホーンは外周にチョークリングを付加することで漏れ電流を防いでおり、scalar ring feedとも呼ばれている。

I read that VE4MA got a good result in 1296MHz EME with this horn feed and 9feet dish combination in the K2UYH newsletter in Aug.1984. And I intended to do a thing, and at first I made this feed horn for my TVRO dish. As the leak current to a rim increase in the simple circular wave guide (so-called Coffee Can), the antenna noise temperature rises because an emission pattern gets worse. This VE4MA horn prevents a leakage current by adding a chalk ring to the circumference portion and is called scalar ring feed.

I cut and brought down an aluminum board of thickness 2mm and I welded (argon autogenous welding) all parts and assembled it. I cut the length of the probe little by little, and return loss of 20dB was obtained in linear polarization. Because 5.5dB of ground noise was observed with my converter of NF0.8dB, the calculated noise temperature of this feed horn is around 30K. 30K - 40K is lower than general coffee can, and is a good level. Because the radiation aperture is large, VE4MA/Barry comments that this feed horn fits to deep parabolic reflector of f/d=0.35 - 0.40. Making was in 1986. This feed was QSY to JH0WJF/Mr.Yaguchi afterwards.



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