As the impedance goes up, the current drops for a given power level drops. John WA4WDL
----- Original Message ----- From: "Hal Murray" <[EMAIL PROTECTED]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Friday, May 11, 2007 3:26 PM Subject: Re: [time-nuts] 50 vs 75 ohm cables > > [EMAIL PROTECTED] said: >> I can confirm that the choice of 75 Ohm for telecom use indeed is >> because of the low attenuation. The first use of coax was for >> "Carrier Frequency" systems, where a number of telephone conversations >> were AM modulated on individual carriers, usually 4 kHz apart. > > What's the attenuation mechanism? > > I thought the old 10 megabit vampire-tap Ethernet picked 50 ohms because > of > lower attenuation. The story I remember is that for a given outside > diameter, the inside diameter was bigger at a lower impedance. The main > losses were resistive on the center conductor due to skin effect. A > bigger > center conductor had more area at a given skin depth and hence lower > losses. > > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
