I hope you have the ladder-line supported by fire-proof (ceramic) insulators in the attic.
Letting ladder-line touch anything combustible can start a fire. Amateur Radio Operator N5GE ARRL Lifetime Member QCWA Lifetime Member On Thu, 15 Nov 2012 13:22:55 +0000, "hawley, charles j jr" <[email protected]> wrote: >I use a 1:1 balun at 450 ohm ladder line to get thru the attic and then 4 inch >open wire outside to the dipole. > >Chuck, KE9UW >Lionel Trains, TCA, LCCA, LRRC >aka Jack, BMW Motorcycles BMWMOA #224 > >________________________________________ >From: [email protected] [[email protected]] on >behalf of Brian Alsop [[email protected]] >Sent: Thursday, November 15, 2012 7:02 AM >To: [email protected] >Subject: Re: [Elecraft] More KAT500 > >This seems so in many cases but it is very doublet length dependent. > >I ran one case in TLW with 45' of 450 ohm line that came out as 13 ohms. > With a 4:1 balun you'd probably be dropping this further. High >current and most likely not a match. > >The best suggestion is to model the antenna at height, get it's >feedpoint impedances at bands of interest. Then go into a program like >TLW with the 450 ohm line length and see what impedance results at the >shack end. > >Adjusting 450 ohm length or doublet length may be required for an >adequate compromise on the bands of interest. > >Without some analysis (or a proven design) it will be a crap shoot. > >73 de Brian/K3KO > >On 11/15/2012 12:31, Jim Wiley wrote: >> Ed - >> >> According to Elecraft, the KAT500 can match 10:1 SWR at 500 watts, on >> any band 80 to 10 meters. It can also match 3:1 SWR at 1000 watts on >> those same bands. The 160 meter and 6 meter capabilities are a bit >> more limited, but it will still match a fairly wide range of loads. By >> inference, 10:1 SWR at 500 watts between 3 and 30 MHz could result in >> peak voltages in the range of 2250 volts and peak currents of 42 amperes >> RF (one or the other, not simultaneously). This is pretty impressive >> for a box that size. >> >> Using those voltages as limits, that indicates that the KAT500 could >> handle power levels of about 250 watts at a 14:1 SWR. Any more could >> result in damage. I would suggest replacing the 300-ohm line on the >> antenna with 450-ohm ladder line, and inserting a 4:1 balun between the >> antenna and the KAT500. I suspect that this will reduce the SWR >> excursions, and may get you "inside the envelope" for what the KAT500 >> can handle. >> >> A commonly used antenna is a doublet (dipole) fed with open wire, a 4:1 >> balun, and a coupler. Most installations use a length of RG-8 coaxial >> cable (typically 10 to 20 feet, but no longer than necessary) to "get >> through the wall" - or from the coupler to the balun immediately outside >> the building, then the open wire line connects to the balun at that >> point and continues to the antenna. 450-ohm ladder line is usually a >> better choice because it is designed for transmitting use, where 300-ohm >> line is usually "TV lead-in" and not particularly suited for use at >> higher power. Some transmitter rated 300 ohm line exists, and if you >> have that type, it may work for you. As with all open-wire type lines, >> keep the line at least 8" to 12" from metal objects if possible, more is >> better, and avoid abrupt right angle turns. >> >> - Jim, KL7CC >> >> >> >> >> >> On 11/15/2012 2:41 AM, Goss, Ed wrote: >>> Hi Jim, >>> Thanks for the info. I am at work now and unable to post back to >>> the group, but I appreciate the explanation. For the low bands, I use >>> a 135 ft inv vee center fed with 300 ohm line, with a 1:1 balun near >>> the shack. When my KAT500 starts to tune itself, I am seeing high >>> SWRs, such as 14:1. After the auto tune cycle, it's 1:1. Perhaps I >>> should be concerned that even with 100 watts, there would be >>> conditions that overstress KAT500 internal parts with this type of >>> antenna, but I want to be very careful about not damaging the tuner. >>> I'm not quite sure how a user would know these limits, or if the >>> KAT500 protects itself in any way. Perhaps the KAT500 is meant to work >>> with antennas that present a somewhat better match to start with, like >>> a typical 80 meter dipole which is cut for CW but the user wants to >>> use all the way up to 4.0 MHz... >>> --Ed--- >>> >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> >> ----- >> No virus found in this message. >> Checked by AVG - www.avg.com >> Version: 2012.0.2221 / Virus Database: 2441/5394 - Release Date: 11/14/12 >> >> > > > >----- >No virus found in this message. >Checked by AVG - www.avg.com >Version: 2012.0.2221 / Virus Database: 2441/5396 - Release Date: 11/15/12 > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[email protected] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:[email protected] > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
