I think a simplified transmitter for measuring field data. A sensor works outdoor and its power takes from indoor power supply. It usually needs 3 wires at least. A pair of 2 wires is more flexible and cheaper than a cable of 3 wires. So I thought to overlay modulated signal with DC power. A frequency modulated modem is suitable. I looked for FSK modem IC. Old FSK modem IC seems to have disappered some years ago. A site uses one of old FSK Bell 202 Standard to receive signal from a satelite. The site introduces 3 modems of TEXAS INSTRUMENTS TCM3105, MX-COM MX614, ConsumerMicrocicuits FX614 and 沖電気 MSM6947. Another site shows a example of FX614 and circuits and a photo of FX614. FX614 is SOP. The other site shows developed software on Windows9x/Me/NT4/2000/Xp to read, display and record demodulated data from the satelite. It shows examples of output of solar panel and 2 directional rotation.
There is a field bus standard for industrial measuring instruments. It is called HART now. I knew they called HART modem. Googling, modems for HART and PLC ( Power Line Carrier ). AMIS-49587 is a modem of Power Line Carrier Modem by On Semiconductor. But it is not available now. DS8500 is a modem for HART by MAXIM. DS8500 is expensive and delivery will be on 20 November 2010. Handling fee is ¥2,000 for Japan.
 SRLL niyoru packet 通信
 SRLL 用 TNC 製作 modem 編
 Amature 通信衛星 wo 利用 shita 電気通信教育
 How HART Works
 HART 実現 no 仕組
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