Performance Data

Gain vs. isotr. Rad.   6.4 dBi
Gain vs. Dipole        4.3 dBD
-3 dB E-plane         69.6 deg.
-3 dB H-plane        133.2 deg.
F/B                   -9.0 dB
F/R                   -6.5 dB
Impedance               50 ohms
Mechan. Length         842 mm
Electr. Length        0.20 λ

Stacking Dist. h-pol.
top-to-bottom          2.3 m or 7.6 ft
side-by-side           n.a

                         - - - - On-Boom-Holders - - - -
        Pos.     Length    BC 25x25   BC 1"x1" BC 30x30
                 in NEC     = 1.4      = 1.5     = 2.1
				 
Refl.     0       2086      2087.4    2085.5    2088.1
DE      842       1938      1930.4    1937.5    1940.1
Ele.      Ø       12 mm     12 mm      3/8"     12 mm

Note: element lengths for Ø 12 mm minus 2 mm fit 3/8"

On-Boom-Holders: see here

The Driver Dipoles diameter is 12 mm for all examples.
Use EZNEC's Auto-Segmentation at 70.2 MHz.

Who has been looking at this Yagi?

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Pattern and VSWR Plots



Elevation and Azimuth plot

 

RL and SWR plot

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Tapered Builds

In some regions a sufficient length of 12 mm or 3/8" tube may be hard to purchase.
So I show how to build a tapered version here. Which same time offers an easy ability
to trim to frequency by adjusting the pushed in lenghts of the outer tubes.

Using 12 and 10 mm tubes for elements you can build a tapered version following the
geometry shown in the sketch below

Element tubes cutting list

Feeding the coax

Use a Quarter Wave Line with a ferrite core towards the split side at the dipole
and an N-flange-bushing on the to-ground side. For any very simple build you might do
without the ferrite core even as long as the QW-line is grounded in a low impedant way.
Which is to use a broad, flat bracket.

How to derive length (a)?

Wavelength is 4.277 m for 70.1 MHz. Length (a) is (4.277 m / 4) x v-factor.
Plus a few millimeters for the frequency depending v-factor of the insulation plastic.
Which usually is around plus 4 ... 5 percent at 70 MHz with means multiplication by 0.96.

For a PE coax that means (a) = 4277 mm x 0.25 x 0.66 x 0.96 = 677 mm
For a foam coax that means (a) = 4277 mm x 0.25 x 0.82 x 0.96 = 842 mm

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Dipole Box

Box is a 'Spelsberg Abox 040 Nautic, Industrial Quality acc. EN 606 70, IP65, free of halogene,
weatherproof, comes with cable gland size M20 spare holes' - 93 x 93 x 55 mm

Inside Closeup: Tube ends carry 2 slots, mid insulator is a glass fibre reinforced plastic rod Ø 11,7 mm by LA4ZH
(www.eidolon.no), 2 hose clamps fastening the mid rod plus connecting stripes made from 1 mm copper.

Boom face side: Making use of the 2 forseen fastening holes and two self cut brackets 35 x 30 mm to
mount to boom on a broad supporting area using a screw M5 x 30 (boom 20 x 30 mm)

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Downloads

EZNEC file of this Yagi with Straight Split DE  

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Stacking


3D pattern plot at 8 m over perfect ground, stacking distance 2.60 m each

with ground gain up to
Gain = 18.9 dBi at 5 degr. of elevation (perfect gnd assumed)
F/B  = 17.9 dB

Free space
Gain = 13.5 dBi
F/B  = 17.8 dB

For more pattern plots see here (2m version)


Stacking Dist. h-pol.
top-to-bottom     2.3 m or 7.6 ft
per DL6WU formula for one pair. See below for carefuly in
EZNEC matched 4 bay with increased stacking distances.



Sketch of 4 x vertical stack, tapered version

Note that due to mutual coupling at close stacking distances as naturally for short Yagis
the idividual Yagis of the stack ahow an adapted geometry to compensate the inter - influences.

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73, Hartmut, DG7YBN