Fred is right about the 450-ohm stuff getting funky in wet weather. Cause my tuners to do the clicky-click dance whenever it rains here, although we've been pretty dry the past few years. Because of this, I plan on replacing my 450-ohm line with 600-ohm ladder line in a couple weeks. I had the 600-ohm stuff on that doublet initially but a change in roofing materials made me change. Long story. Anyway, as you probably know, antennas work much better when built or adjusted when the weather is horrible!!!
Jim / W6JHB > On Oct 17, 2014, at 4:57 PM, Fred Jensen <[email protected]> wrote: > > Don pretty much described my low band antenna. Full Disclosure: I live on 5 > acres and have a 70' tower. That said, it is a Sloping V [I'd call it an > inverted V except is isn't resonant on any band], about 210' on a side from > the top of the tower. 450 ohm window line to the bottom of the tower, DXE > 4:1 balun, and coax into the house. I have chokes on the coax at the balun > and at the weatherhead entrance, but I've never had any problems with RFITS > [RF In The Shack] with or without the chokes. > > It works well on 80-40-30, requires a tuner of course [KAT500]. Works on 160 > but warms the clouds and worms, I use an Inv-L for top band. It also works > on all the bands up from 30 but the pattern gets fairly complex and squirts > my RF in a lot of non-productive directions because it's so big. > > My experience is that an 88 ft doublet, center-fed, works really well on 40 > and up in frequency, often used by those activating summits in Summits On The > Air. Shorter doublets are also effective, and not being resonant doesn't > really matter [in some cases, it helps]. Neither does what you do with the > ends. Most of the radiation comes from the center, high current sections. > > 450 ohm window line is sensitive to moisture ... if you set up your tuner for > dry conditions and it's now raining, things will need retuning. > > Keep in mind the wisdom of Tom, N6BT, "Anything conductive will radiate if > you get power into it." > > 73, > > Fred K6DGW > - Northern California Contest Club > - CU in the 2015 Cal QSO Party 3-4 Oct 2015 > - www.cqp.org > >> On 10/17/2014 3:54 PM, Don Wilhelm wrote: >> >> Make it a balanced dipole antenna (equal lengths on either side of the >> feedpoint) for best efforts in keeping RF off the feedline. The actual >> length does not matter a lot, but it should be greater than 80% of the >> half wavelength for the lowest band of interest. >> >> Use open wire line or 450 ohm ladder line to feed it down to the point >> where it enters the shack - hopefully you can run the feedline >> perpendicular from the radiator for at least 1/4 wavelength on the >> lowest frequency of interest for lowest radiator to feedline pickup. Put >> a good 1:1 current mod choke at that point. See page 29 of K9YC's RFI >> tutorial http://www.audiosystemsgroup.com/RFI-Ham.pdf >> for instructions on how to construct a very effective current mode choke >> - note: a good balun *is* a current mode choke, but many fail to perform >> as well as the ones tested by K9YC. >> >> You will need a tuner, and any Elecraft tuner should do the job nicely. >> If it does not, then you may have to make some adjustments in the length >> of the parallel feedline to see if you can achieve success on all bands >> of interest. >> >> You may want to take a look at the Antenna and Transmission Line article >> on my website www.w3fpr.com for a bit on non-math theory on antennas. > > > ______________________________________________________________ > 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 > Message delivered to [email protected] ______________________________________________________________ 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 Message delivered to [email protected]
