Fwd: Re: antenna farm

[Jim Dunstan]

>Date: Mon, 14 Dec 2009 14:38:33 -0500
>To: "Clint" <[hidden email]>
>From: Jim Dunstan <[hidden email]>
>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
>
>
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>
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