Quote: “In AC power lines little is paid attention to as for transmission except for R losses and power factor.”
I can remember doing an experiment in college where we needed 60 HZ exactly and would have to call the generation plant to see if they were running at 60 HZ. I never did think we could guarantee we had 60 HZ as the Z will change somewhat with distance from the plant. That is why the power companies put large capacitors in the line to bring it back in phase. Quote: “Yes up the voltage/lower the current and the IR loss goes down.” This brought back a laugh as I once ran 500 foot of extension cord to run a circular saw. Wasn’t getting much done so I hooked it up to 220 volts source. Had about 140 volts under load. You could saw till the blade turned blue. Randy B. -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Ron Wright Sent: Wednesday, August 29, 2007 10:32 AM To: Repeater-Builder@yahoogroups.com Subject: Re: Re: Re: Re: RE: [Repeater-Builder] Re: Duplexers Ralph, Transmission line theory for RF and AC power is totally different. In AC power lines little is paid attention to as for transmission except for R losses and power factor. Yes up the voltage/lower the current and the IR loss goes down. For RF this is totally different for the RF propergatesdown the line, not just passes as voltage and currents. This is why feedlines have specific impedances and loads used. One can have any impedance of coax or twin feeds one wants...that is if you have the material and space for it. One can get off the shelf 75 Ohm twin lead. Using 50 or 75 Ohm has more to do with stability especially at RF. IR drops in feedlines is much less than a factor than the LC/dielectric type losses. Again frequency shows this. 100 W at 10 MHz and 1000 MHz will have radically different losses yet both have the same I and V and R. 73, ron, n9ee/r >From: Ralph Mowery <HYPERLINK "mailto:ku4pt%40yahoo.com"[EMAIL PROTECTED]> >Date: 2007/08/27 Mon AM 09:20:07 CDT >To: HYPERLINK "mailto:Repeater-Builder%40yahoogroups.com"[EMAIL PROTECTED] m >Subject: Re: Re: Re: RE: [Repeater-Builder] Re: Duplexers > > >--- Ron Wright <HYPERLINK "mailto:mccrpt%40verizon.net"[EMAIL PROTECTED]> wrote: > >> Jesse, >> >> Then why do twin feeders have much less loss than >> coax??? Skin affect is even more of a factor there >> due to the differences in the area of the outer >> shield in coax vs the twin feeders wire. >> >> Maybe it is because of the larger C coupling in the >> coax due to the larger surface area of the shield. >> Coax has a lower R even with skin effect than twin >> line feeders. >> >> Skin affect is a factor, but a small one compared to >> the LC factor. >> >> 73, ron, n9ee/r >> > >It is not open wire or coax that determins the power >loss. It is the impedance of the line and the size of >the conductors for frequencies up to 1000 Mhz or so. > >To transfer 1000 watts of power , the voltage will be >higher and the current lower in most prectical open >wire lines. That is because the impedance will be >around 300 to 600 ohms. Coax is usually 50 or 70 >ohms. To get 1000 watts of power through that >impedance line it requires less voltage and more >current. > >This is the principal of regular 60 hz power line >transmission. Up the voltage to a few hundred >thousand volts and the current will go down. This >lowers the losses. > >I don't care to take time to do the calculations, but >if you take some small guage wire (say # 20) and >space it close to make about 200 ohms line and figuer >the loss, it may be higher than some 1 inch or even >1/2 inch hardline. > >At frequencies below around 1000 Mhz the major loss is >the IsqR loss in all lines. Radiation is a very small >part. In coax there is a point in which the current >on the shield is not flowing but jumping from point to >point where the shield wires cross. This causes some >resistance. That is partly why the foil shielded coax >and hardline is lower in loss than regular coax. > >___________-_________-_________-_________-_________-_________-__ >Be a better Heartthrob. Get better relationship answers from someone who knows. Yahoo! Answers - Check it out. >HYPERLINK "http://answers.yahoo.com/dir/?link=list&sid=396545433"http://answers.-yahoo .com/-dir/?link=-list&sid=-396545433 > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007 12:00 AM No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.6 - Release Date: 8/24/2007 12:00 AM
