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* * *  ROTARY DIPOLE FOR 12/17 mt * * * by IK4DCS

 

ROTARY DIPOLE 12/17 MT

After all the  experiments on the WARC bands self-made antennas I had just to
try with a coax-cable-trapped rotating dipole.
I already had experimented this type of construction on other types of antennas
and I just wanted to  complete the series of 24/18 Mhz with a new dipole in
order to check the electrical/mechanical differences.
When one decides to start with self-construction one supposes to have all the
necessary material already at disposal and at hands reach.
Therefore check, first of all the following suggestions:
Make sure that all the drill gear is perfectly sharpened, that the saw blade
is new, and that your preferred hardware  shop is open for the latest unexpected
purchases.


Ok, let's get started.

Look for a 27 mm. diam. pipe  long as 0,5 mt.(2 pieces), two pipes as long as
1,20 mt. 24 mm. pipe. Another two pieces as long as 0,50 mt.  20 mm. pipe,
anther two pipes long as 0,25 mt. 16 mm. diam. pipe, and then 2 pipes  with a
8 mm. diam. and as long as 0,50 mt.  Then take a 40x40x1550 mm square pipe, 8 nylon insulators with a 30 mm. diam, shaped as.....see the photo for to how.
Again take a PVC water pipe  with a 32 mm. diam and long as 100 mm. (2 pcs),
the nd 4 teflon or nylon rods  with a diam. of 30 mm. and a supply of RG58
coax cable.
Let's now start from the assembly of the support bound to bear the dipole:
the 40x40x1500 mm square tube must be drilled in order to take in the insulators.
 

Then after having also drilled the 27 mm. aluminum pipe at the same position as the square tube, fix the 8 x 100 mm. bolts to fix the first part of the dipole
betwen insulators and the square (see picture). Now insert the 24 mm.pipe inside the 27 mm. pipe for about 25/30 cm. and let's drill two holes that will be necessary to fix with screws the two pieces. Take attention to the hole diam.: 5 mm. outside, 2,5 mm. inside using screws of 5x10 mm.
The outside end of the 24 mm. pipe make two cross cuts creating so 4 blades that must accept the 20 mm. pipe fixed with appropriate metal clamps.
Mount the 20 mm. pipe inserting it for abt 20 cm. inside the 24 mm. tube.
Put a clamp and fix it well. The same must be done with the 16 mm. pipe inside the 20 mm. tube for abt 15 cm. inside. Fix the metal clamp.
Well, at this stage we have realised the first part of our dipole.
Now let's make a flat base of 5x100x250 mm., check the diam. of your mast and find, buy, or make the 4 TV type clamps necessary for the attachment.
Look at the pictures and mount the clamps so as two of them support the dipole on the plate and two the plate to the mats.
Let's now take the dipole and balancing it on a finger let's try to put it on
a level. Find the central position, fix it and tighten the clamps.
Now we have to set the whol thing for 24 Mhz.
At the center of the dipole it is necessary to mount a 1:1 balun of any kind.
It is up to you to make the most suitable choice.
Tune the dipole , take the 32 mm. PVC pipe and wind about 4 spires of RG58
cable in orde to prepare our trap.
Don't be too much worried if you do not have the necessary instruments:
just make the traps and put 20 mm. pieces inside the 32. mm.
Drill them in order to accept 16 and 8 mm. pcs  inside and outside.

To complete the trap have a look at any text concerning wire antennas and then mount the traps, so made, at the ends of the dipole already tuned on 24 Mhz. Make the necessary action on the traps so as to get  to the necessary frequency.
If low, shorten the wire at 10 mm. steps, if too high make a longer coil.
At the end of these necessary tunings mount the 8 mm. pipe inside the hole made on the nylon inserted in the trap.
If you also want to make a protection to the trap for bad weather conditions, use a pvc tube; look at the picture.
Approximately  46/47 cm of length of the tip should be enough, nut all dipends
on the length of your dipole on 24 Mhz.
As always, with this new self made antenna, results were great, either as far
as mechanical and electrical aspects were concerned.
For sure, with this antenna  many people will hear from you strongly on these
bands.

Have a nice time.
I remain, as always at full disposal for any further suggestion .

IK4DCS - Franco


 

English version by

IK4CIV - Vincenzo