[Elecraft] RF in the Trees

Fri Jun 27 06:16:40 EDT 2014

Thanks very much for showing me HYpower Anntennas.  They look very interesting, and I am going to call them with questions.  Gerry

Sent from my iPhone this time 

> On Jun 26, 2014, at 9:39 AM, Walter Underwood <wunder at wunderwood.org> wrote:
> 
> For pre-built antennas, HyPower is a good choice. He has lots of options, fan dipoles, loaded dipoles, even combinations. I have a fan dipole made from a full-size 40m element and an element that is full-size for 80 and loaded for 80. He also sells the loading coils if you would rather DIY.
> 
> http://www.hypowerantenna.com/
> 
> wunder
> K6WRU
> 
>> On Jun 26, 2014, at 5:30 AM, "Charlie T, K3ICH" <pincon at erols.com> wrote:
>> 
>> Don't rule out traps.
>> 
>> Also, the RF Connection and probably others, sell a nice stranded copperweld wire that has a black polyethylene insulation.  If I remember correctly, it is 13 ga and is ideal for antennas.  For all practical purposes, it doesn't stretch,  is fairly slippery  and only a little "springier" than hard drawn copper.
>> 
>> I use those double ferrule aluminum crimp on's that are designed for flexible wire cable to hold everything together.  I was concerned about them holding through the poly insulation, but the following antenna has been up for about ten years now.  It consists of a double (fan) dipole with a pair of 80 meter traps in the top leg for 160 & 80 M coverage and a pair of 40 meter traps in the lower leg for 60 & 40 M coverage.  It is fed thru a 1:1 balun with RG-213 and is tuned for resonance.  Basically, I operate SSB 99% of the time, so the antenna is tuned for that end of the bands.  An MN-2700 tuner in the shack takes care of  small excursions from resonance.  It's only up about 50 feet, so performance is what you'd expect. It's not straight either and is sort of a lazy Z, being strung between two 55' telephone poles that are 105 feet apart.  The ends droop down at about 45 degrees to tie-off points in trees.  A compromise? Yes, but it works.
>> 
>> 73, Charlie k3ICH
>> 
>> 
>> 
>> 
>> ----- Original Message ----- From: "Jim Brown" <jim at audiosystemsgroup.com>
>> To: <elecraft at mailman.qth.net>
>> Sent: Thursday, June 26, 2014 1:55 AM
>> Subject: Re: [Elecraft] RF in the Trees
>> 
>> 
>>>> 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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>> 
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> 
> --
> Walter Underwood
> wunder at wunderwood.org
> 
> 
> 
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