DG7YBN / 70 MHz / YBN 4m-2w
  Last Update July 2nd 2015


Performance Data and Geometry
Pattern and VSWR
Tapered Version & Building Hints
Dipole Box
Download as File

YBN 4m-2w: Simple, easy to produce 2 Ele. Yagi

This little Yagi is as much bandwidth as can be. A forgiving and easy to build alternative to the HB9CV.
Take a view at the stacking section: 4 x 2 elem. vertical produce 13.5 dBi at a HPBW of 71 degr.
You will not miss any ES opening with this broad and flat main beam!

It does not have the HB9CV's famous F/B ratio but is much easier to build, no phasing lines, no capacitor ...
Nothing to protect from rain and snow. When you ar portable with a little antenna and little rig anyway
a high F/B does not help much. And note that the HB9CV's true gain is around 4.15 ... 4.2 dBD. No more then that.

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.

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Pattern and VSWR Plots

Elevation and Azimuth plot


RL and SWR plot

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

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)


EZNEC file of this Yagi with Straight Split DE  


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.

73, Hartmut, DG7YBN

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