>Date: Mon, 14 Dec 2009 14:38:33 -0500 >To: "Clint" <clint.st...@sbcglobal.net> >From: Jim Dunstan <jduns...@tbaytel.net> >Subject: Re: [Elecraft] antenna farm > >At 10:17 AM 12/14/2009 -0800, you wrote: > > >>So my questions are: >> >>1) What length would be best and give me the use of the most bands? >>Remember, I have a limited space. >> >>2) How far from the dipole should a reflector be. It should be about 5% >>longer and grounded, right? >> >>3) The auto-tuner on the K3 is amazing. Is it easier for it to tune >>an antenna that is to long or to short? I'm guessing long but I am not >>certain. >> >>4) Any suggestions on which band/antenna length is best for these >>targets? I am mostly active late afternoon and evening (till about 10 >>PST) and mornings after 6. >> >>Thanks, >> >>Clint KI6SSN > >I believe you missed out the most important question concerning a dipole >.... height !! > >The radiation pattern of a dipole is basically broadside ... and maintains >that pattern (with increased broad side gain) as it is made longer up to >approximately 1 wavelength or a bit more. After this length the >(horizontal) radiation pattern starts to break up into multiple lobes >(making the pattern unpredictable). That eminent antenna Guru ... Cebik >... studied this phenomena and stated that the dipole/doublet can maintain >the predictable radiation pattern over a 4:1 frequency range. > >Given this 4:1 range you could choose 10m as the highest frequency .... >making 44 ft the doublet length covering 40-10m.... or choose 20m .... >making the 88 ft doublet covering 80-20m. In both cases it becomes >difficult (but possible) to feed the antenna at the lowest frequency (40m >in the first case of 44 ft ... and 80m in the second case of 88 >ft). However 44ft is great for 30-10m and 88 ft is great for 40-20m. > >You have to realize that the doublet in either length is non-resonant ... >and will have to be fed either with an antenna coupler ... such as those >made by SGC followed by coax... or a low loss balanced feed line and >antenna tuner. > >I personally like the 44 ft version as it can be constructed as a >rotatable dipole .... I feed mine with open wire line to a balanced tuner >in the shack. it is mounted at 55ft height .... ideal for 10 & 15 mtrs >.... very gud at 20m .... and just gud at 40m. I use a different wire >antenna for 80m. I can rotate it ... but rarely need to do so. except >when propagation is clearly needed north and south ... otherwise it is >always broadside to east and west. > >I have no difficulty working DX 30-10m and occasionally with 40m. > >However getting the doublet up in that 50-70 ft range is much more >important than which way it faces. Here in N.A. getting the wire >broadside to E.W. is all you need for a start. there are some Antenna >reflectors that discuss this topic regularly. > >Jim, VE3CI > > > > > > > > > >>__________ Information from ESET NOD32 Antivirus, version of virus >>signature database 4687 (20091214) __________ >> >>The message was checked by ESET NOD32 Antivirus. >> >>http://www.eset.com >> >>______________________________________________________________ >>Elecraft mailing list >>Home: http://mailman.qth.net/mailman/listinfo/elecraft >>Help: http://mailman.qth.net/mmfaq.htm >>Post: mailto:Elecraft@mailman.qth.net >> >>This list hosted by: http://www.qsl.net >>Please help support this email list: http://www.qsl.net/donate.html
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