Homemade 15 meter Rotatable Coil Dipole

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Homemade 15 meter Rotatable Coil Dipole

Postby ka4ngw » Thu Mar 05, 2015 3:36 am

Ok here's the deal, I am going to do my first DX contest this weekend and can radiate very good on all bands except 15 meters.
Question: Using two 6 ft 1/2 inche PVC, is it possible to wrap each side with 11.11" of wire to make like a coiled dipole? I need a answer fast. Well actually I am building it anyway to see if it works.
I know SKCC is more of a CW forum but hey its my first since becoming a Ham 35 yrs ago.
Thanks for any info
Thanks Paul KA4NGW/7 13615
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Re: Homemade 15 meter Rotatable Coil Dipole

Postby WB2VVV » Fri Jun 26, 2015 3:22 pm

How did your hand wound helical dipole on PVC pipe work out?

I have experimented with helically wound dipoles before and found them very touchy to get them to resonate exactly where I wanted. I wound them as you suggested on a form, and also even used slinkys suspended on a rope. For me, they all ended up needing to be used with a tuner, but they certainly made contacts. Generally speaking it's been my experience that if you can build a loaded/shortened dipole 1/2 to 2/3 the physical length of a standard size dipole they work like you would expect a standard size dipole to work (within a dB anyway).

I later built a dual band rotatable dipole which I used for a number of years without a tuner for 10m and 20m, and it worked very well. It was made of some pipe the physical length of a 10m dipole, and at the far ends I bolted on a short coil form with a capacitive hat beyond the coil form and an 18 inch or so long tuning tip beyond that made of brass rod for fine electrical length tuning on 20m. The tuning tip was soldered to the brass plate holding the capacitive hat (which itself was a dozen or so brass rod pieces around 6 inches long soldered to a brass mounting plate) and I trimmed the length of the tuning tip with a set of side cutter pliers with the dipole temporarily atop a 10 foot tall step ladder - while checking VSWR. This was before I installed it since I wouldn't be able to get to the tuning tips after. The concept of this dual band antenna was essentially to place a large lumped inductance right beyond a plain standard size 10m dipole, which would become part of the resonant 20m dipole when operating on 20m but not have much effect on 10m. The tuning rod allowed me to make fine adjustments for the 20m resonance and once adjusted the antenna worked great on both bands without a tuner. It exhibited the typical pattern of a standard size dipole when rotated, and was a solid performer. Incorporating this sort of tuning tip may be what you need to tweak your helical dipole to the right resonance.

For a shortened single band rotatable dipole you could always use two "Ham Stick" type mobile whips for the band of your choice, which include fine tuning "Stinger" tips.

73, Chris WB2VVV
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