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Strategies & Market Trends : Anthony @ Equity Investigations, Dear Anthony, -- Ignore unavailable to you. Want to Upgrade?

To: Jim Spitz who wrote (7049)	1/29/1999 8:33:00 AM
From: Marshall	Read Replies (1) \| Respond to of 122087

Jim - it obviously works fine or Microsoft would have never allowed their name to be used in the press release on it. If you're a EE you should be aware of the buck/boost converter ICs that have been around for some time. I'll make these numbers round so you can follow along. The nominal resistance of a station (phone) is considered to be 400 ohms. A phone line normally has 60 - 70 volts on it so let's use 66 volts. Buck/boost converter ICs can easily produce an 80% efficiency. OK, let's say the modem requires 800 mA at 3.3V, to get this you'd only need to draw 50 mA from a 66 volt phone line if your converter IC was operating at 80% efficiency. That nominal 400 ohm terminal (phone) I mentioned would have been drawing 165 mA were you using it instead of the modem. Of course the modem itself is going to use a little line current on its own for the line connection but I think we can consider the combined draw from the line to be well within the specs that the FCC allows for any device connected to a line. If you want to put some headroom into the equation consider the fact that your connection works just fine even if two people in the house are both talking on the same call which would mean 200 ohms connected to the line. It's simple math, try to draw it out on paper and it should make sense. I realize that they don't really teach a lot about telephony in school unless you opt for a Master's in the subject at a school that offers the courses. I'm kind of lucky as my next door neighbor is a semi-retired AT&T exec and next to him is the guy who recently retired as the Senior Engineer for SW Bell (SBC) and he currently teaches courses down at OU. Most of his students are actually beginning engineers that WorldCom sends over from Tulsa.