DG7YBN / 432 MHz / GTV 70-7w
  Last Update June 1st 2019


Performance Data and Geometry
Pattern and VSWR
Download as File

GTV 70-7w Yagi   with bent Driven Element

Wideband version ... 430 to 438 (440) MHz

This Yagi has very low back lobes for its length and bandwidth.
Simulated Return Loss (S11) is better -30 dB from 430 to 438 MHz. It may serve as single antenna for portable
use and is easy to repoduce. It certainly makes a useful 4 x vertical stack. It makes a quiet contest antenna due to its
high F/B. The bent DE (K6STI style) transforms from approx. 17 ohms to 50 ohms at feed point.

This designs origin is the YBN 3+7 SAT handheld combination Yagi.
With M0ABA having built it the first thing he did was a moon bounce test,
which went well with only 60 W at the feedpoint.

See building details and screenshots of the EME QSO on the SAT Yagis website

Current distribution

3D Pattern (432.1 MHz)

Performance Data

Specs: with 6.35 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  12.3 dBi
Gain vs. Dipole       10.1 dBD
-3 dB E-plane         44.3 deg.
-3 dB H-plane         52.2 deg.
F/B                  -26.5 dB
F/R                  -21.5 dB
Impedance               50 ohms
Mechan. Length         960 mm incl. 2 x 30 mm stand off
Electr. Length        1.30 λ

Stacking dist. h-pol.
top-to-bottom         0.79 m or 2.59 ft
side-by-side          0.92 m or 3.02 ft

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Table 1: 70 cm section, 6.35 mm elements through a 5/8 inch boom,
formast mount with 280 mm offset on rear boom end:

"Ready to saw and drill" data for mounting elements through boom with BC according SM5BSZ's BC.exe:

This table is only valid for:
Boom shape: square
Boom dim: 5/8 x 5/8 inch
Wall thickn.: 1/6 inch = 1.6 mm
Holes in boom: 8.0 mm
Offset rear: 280 mm
Offset front: 30 mm

Note: This does include an SBC of 1.74 mm plus a correction for the insulators (v-factor!) of 0.7 mm = 2.44 mm

Note: with through Boom BC it is important to stick to the boom end offsets given below!

For making of a 'Blade Dipole' which I recommend for elements through boom builds

Sketch of Bent Dipole

Radiation Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz (6.35 mm ele.)


SWR and Return Loss plots - simulated with 4nec2

M0ABA plotted Return Loss 70 cm: -44 dB at 435.5 MHz

Elevation Pattern 430 - 438 MHz




none so far


Stacking Dist.    DL6WU Formula
H-plane               0.79 m
E-plane               0.96 m

A 4 Yagi bay

Elev. and Az. Plot @ 432.3 MHz


Data for elements 6.35 mm @ 432.3 MHz

Gain vs. isotr. Rad.  18.25 dBi
Gain vs. Dipole       16.10 dBD
-3 dB H-plane, appr.  19.8 deg.
-3 dB E-plane, appr.  23.2 deg.
F/B                  -29.4 dB
F/R                  -23.9 dB
T_ant                140.1 K*
G/T                  -3.21 dB*
Theoretical numbers, no phasing line losses
nor imperfections caused by mast included
*) T_sky = 27 K, T_earth = 1800 K as in newer VE7BQH G/T table

3D pattern plot with 4nec2's 3D viewer

4 x vertical Stack at 770 mm each

Elev. Pattern @ 432.3 MHz

8 x vertical Stack at 770 mm each

Elev. Pattern @ 432.3 MHz

Symmetrising 50 to 50 ohms feedline to 432 MHz Bent DE

The principle is similar to the 1/4 Lambda coax. Adding 2 x 1/4 Lambda or a half wave line does not change anything but allows
to form a gentle bow below the boom or until behind the Reflector. Follow practical construction hints on "Building a Yagi" page.


  Attenzione!     Take care when lengthening the coax, measure the actual electrical length instead of considering v-factors specified in a catalogue only.
                                      A good choice may be the diam. 5 mm PTFE coax RG-142 B/U: real resonate length (432.2 MHz as 3/4 Lambda) shield-shield is around 348 mm

  Find more information on Phasing & Matching Lines page

73, Hartmut, DG7YBN

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