004: 433MHz FM 2W transceiver (6939)

 ローカル局との定期連絡用に製作したFMトランシーバ。送信部は東芝のタクシー機ジャンクから取り出したユニットで、原振18MHzで可変リアクタンス変調をかけて2逓倍したあと、12BY7A(×2)-12BY7A(×2)-6939(×3)-6939により433MHz帯で3Wを得ている(Ep 175V)。元々は450MHz用なので各ステージのプレートとグリッドに適宜コンデンサを追加しながら励振段を同調させ、目的の433MHzに合わせこんでいった。

This is an FM transceiver that I made for regular contacts with local stations. The transmitter part is taken out from an old Toshiba taxi radio, and it obtains 3Watts on 433MHz (Ep 175V). The block diagram is, osc-variable reactance modulation on 18MHz-doubler -12BY7A(×2) -12BY7A(×2) -6939(×3)-6939. I properly added some condensers to the plate and the grid of each stage to get a good excitation on 433MHz because it was tuned originally for 450-460MHz.

For the receiver part I also used the junk-unit of a Hitachi business transceiver as the IF /AF PCB. The home brew converter (433→10.7MHz) was consisted of a couple of Hitachi 3SK70’s in the top and mixer and the sensitivity was pretty good. Making was done in my student residence in Tokyo/Setagaya at twilight of 1979, and I started to use it for JA0DLA et al. in the spring of 1980 frequently just after I returned to Matsumoto.




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