DG7YBN / 432 MHz / GTV 70-34w
  Last Update Jan. 21st 2018


Performance Data and Geometry
Pattern and VSWR

GTV 70-34w Yagi   with bent Driven Element

432.1 MHz EME to 436 MHz Longyagi as Wideband Antenna Version (OWA-style)

This Yagi has very low back lobes for its length. It may serve as single antenna for Tropo
or make a nice 4 Yagi EME array. It also 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.

What else? With this Yagi I stopped producing more forward gain keeping the directivity factor
at a point that I see as uncritical still for producing nicely working real world builds.
Antenna G/T can be pushed further but with increase of Antenna Temperature mainly.
Which I did not want to do. In my understanding the 34 element Yagi should not hold a higher
Antenna Temperature than the GTV70-30m.

The GTV70-34w produces a solid 0.5 dB higher G/T compared to the GTV70-30m which by
all means should show in its performance for EME and other Weak Signal operations.

Current distribution

Performance Data

Specs: with 8 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  20.3 dBi
Gain vs. Dipole       18.2 dBD
-3 dB E-plane         19.6 deg.
-3 dB H-plane         20.0 deg.
F/B                  -40.5 dB (34 dB)
F/R                  -33.8 dB
Impedance               50 ohms
Mechan. Length        8455 mm
Electr. Length        12.18 λ

Stacking Dist. h-pol. acc the DL6WU formula

top-to-bottom         1.998 m
side-by-side          2.038 m


Geometry for 8 mm elements     

The Drivers diameter is 10 mm for all examples. Use EZNEC's Auto-Segmentation at 1050 MHz.

A simple symmetrising member may be made from a 3 x 1/4 Lambda line grounded at the far side with
N-flange-bushing and an aluminium plate and ferrite added as close as possible to the DE, see below.

How many OMs have been looking up this design?

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Ø8 mm Elements - On Boom - Dimensions (BC acc. DG7YBN)     

Actual BC for on a 25 x 25 mm Boom with standard insulators is 11.0 mm, SBC is 1.37 mm,
total length to add is ~ 12.4 mm

Using a large calliper gauge to control element lenghts to a 10th of a millimeter is a must.

Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz


SWR and Return Loss plots - simulated with 4nec2


As on the 432 MHz Band the Y-factor = T_earth / T_sky is that high I see little chances in
bettering an array's RX performance by using "Over Stacking" distances. However, depending
the level of local QRM it might be worthwhile to try less distance, especially in H-plane.

Stacking Dist.    DL6WU Formula
H-plane               2.00 m
E-plane               2.04 m

Elevation and Azimuth plot and data of 4 Yagi bay using DL6WU stacking distances

AGTC_lite screenshot of this Yagi with 8 mm elements

Gain vs. isotr. Rad.   26.10 dBi
Gain vs. Dipole        23.95 dBD
-3 dB H-plane, appr.  -.- deg.
-3 dB E-plane, appr.  -.- deg.
F/B                   -.- dB
F/R                   -.- dB
T_ant                  26.2 K*
G/T                   11.91 dB*

Theoretical numbers, no phasing line losses
nor imperfections caused by H-frame included
*) T_sky = 20 K, T_earth = 350 K as in VE7BQH G/T table

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 right length instead of refering to given v-factors 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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