[Elecraft] RF in the Trees

[Doug Person via Elecraft]

The K9YC modelling with EZNEC 
<http://k9yc.com/VertOrHorizontal-Slides.pdf> is quite interesting.  
Certainly has me thinking about vertical dipoles.  The half-wave end-fed 
looks like the perfect candidate for a simple vertical dipole.

Doug -- K0DXV

On 6/25/14, 11:55 PM, Jim Brown wrote:
> On 6/25/2014 5:43 PM, Dauer, Edward wrote:
>> So, I've been selecting two of the tallest
>> candidates a couple of hundred feet apart and stringing a stout nylon 
>> rope
>> between them.  In the middle of the cord I attach the balun for the 
>> Vees,
>> thereby allowing the legs to be in the clear, moveable from side to 
>> side,
>> and tied to smaller (8') trees at their distal ends.  In one 
>> variation on
>> the theme I had a 40 meter dipole as the center section of the 
>> supporting
>> rope, tied to the same balun as an 80 meter vee.  In another I tried a
>> linear-loaded 80-meter Vee, about 45' on a leg; it loaded fine but 
>> didn't
>> perform as well as the full length version.
>
> If you can suspend a flat antenna between two tall trees, why would 
> you want an inverted vee, which is a less effective radiator?
>
> Your two trees 200 ft apart could support a full size 80/40 fan and a 
> 20/15/10 fan, in line with each other. A high 80/40 fan is a VERY good 
> antenna, and is easy to build.
>
> My technique has evolved to starting with #8 bare copper from the big 
> box store, stretch it VERY slowly between a tree and a trailer hitch 
> until it breaks. Do this carefully where there's no one around to get 
> hurt. Now you have #10 hard drawn copper, which is pretty strong, and 
> pre-stretched. Use that for the longest dipole in each fan. Use #12 or 
> #14 THHN (house wire) for the other elements. I make spacers by 
> cutting 1/2-in PVC conduit into lengths of about 16 in for 3-wire 
> fans, and about 12 inches for 2-wire fans. 5-6 ft between spacers is a 
> good rule of thumb. Hold the spacers in place by soldering short 
> lengths of copper around the spacer to the bare copper of the long 
> element.
>
> The higher your antenna is, the more robust your center insulator 
> should be. A high 80/40 dipole (80 ft or more) will be closer to 75 
> ohms than 50 ohms. A 20/15/10 fan will be close to 50 ohms. Use RG8 or 
> RG11 depending on the Z at resonance. Don't waste a dB or two with 
> small coax. My 110 ft 80/40 fans are fed with Belden 8213.
>
> For weights, I fill 6 gallon water jugs with dry sand, and tie one to 
> one end of each span. The other end can be fixed. I have pulleys high 
> my trees. If you don't have a pulley and weight, your antenna WILL end 
> up on the ground, and it won't take a big storm for that to happen.
>
> My HF antennas are all at the 110-120 ft level in a dense redwood 
> forest that towers 50-75 ft above them. They work. My "seat of the 
> pants" observation is that attenuation increases with frequency, and 
> is greatest with vertical polarization. 432 MHz is a waste of time, 2M 
> sort of works, and 6M works pretty well.
>
> For an analysis of the value of height, study this. It supports the 
> statement earlier in this thread that a high dipole beats a low 
> tri-bander.
>
> http://k9yc.com/VertOrHorizontal-Slides.pdf
>
> When Fred observes that the ends of antennas are "hotter," he means 
> that this is voltage maxima and a current minima, so good insulation 
> is needed to whatever the antenna is attached. I once melted heavy 
> dacron rope that was tied directly to the end of said dipole (well, 
> twice, actually). The extra ingredient was that it was wet. Duh.
>
> 73, Jim K9YC
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