[Elecraft] RF in the Trees

Fri Jun 27 13:40:18 EDT 2014

I don't really understand why traps have gotten such a bad rap. Consider 
that most all triband beams use traps as well as many verticals.  I have 
been using Spi-Ro traps for 20 years and never had a problem and I 
certainly don't see any indication that I am suffering some kind of loss 
as a result.  I have made many comparisons between the trapped dipoles 
and single band non-trapped dipoles and the only difference I see is a 
reduction in usable bandwidth.  The Spi-Ro traps are rated for 600 watts 
making them perfect for the KPA500 powered station.  Indeed - do not 
rule out traps.

I also use a similar wire that to what Charlie mentions.  Last order was 
for 600 feet. It's great stuff.

Now I'm thinking of what would be the best "all-band" antenna for the K2 
which is my secondary operating position in the living room where I can 
give demos to visitors.  I'm thinking of giving the 88 foot doublet fed 
with 300 ohm twinlead a try.

Doug -- K0DXV

On 6/26/14, 6:30 AM, Charlie T, K3ICH 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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