DG7YBN / 432 MHz / GTV 70-30m
  Last Update Feb 25th 2018


Performance Data and Geometry
Pattern and VSWR
Folded Dipole Version
Download as File

GTV 70-30m Yagi   with bent Driven Element

EME + SSB band Longyagi

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.

GTV 70-30w Rope built by Marek, SP4ELF
Testing with help of Marcin SQ4CUC, Alexander RA2FGG and Romek SP4JCP in -10 C frost produced 2 QSOs in JT65.

Marek:"We have recovered many traces of EME stations but the conditions did not allow for longer work. We had
difficult weather conditions, frost -10 degrees and snowfall, clouds. Despite everything, the antenna worked
very well. Our equipment is FT857 and 200W we did not use LNA for technical reasons."
   Click for large photo

Sub-Website with more info on this rope Yagi

Close up on bent dipole: note symmetrising by Pawsay Stub

Cuttings from plastic tube for element fastening: (mind ... the shorter the better for best rf properties)

GTV 70-30w Rope built by Thomas, M0ABA at MX0CNS
Look at this: A close to 8 m long GTV 70-30m Rope Yagi built on Kevlar Kite lines,
4 mm elements and a 1/4 λ sleeve with Pawsey symmmetrising ...

Click here to see the full frame photo
There are details and all the news to be posted shortly about this antenna on the MX0CNS facebook

M0ABA at MX0CNS: Screenshot of WSJT of first QSO with the Rope Yagi, beam slightly off the moon still,
60 W at feed at MX0CNS <> DL7APV

GTV 70-30m built by Chris, PA2CHR with 8 mm Elements on Boom, BC acc. DG7YBN

Current distribution

Short Screenshot Movie showing rotating 3D Pattern

To watch the rotating 3D Pattern movie by F5JM click here pse

Performance Data

Specs: with 4 mm elements @ 432.1 MHz

Gain vs. isotr. Rad.  19.7 dBi
Gain vs. Dipole       17.6 dBD
-3 dB E-plane         20.6 deg.
-3 dB H-plane         21.2 deg.
F/B                  -33.8 dB
F/R                  -33.8 dB
Impedance               50 ohms
Mechan. Length        7276 mm
Electr. Length        10.48 λ

Stacking Dist. h-pol.
top-to-bottom         1.89 m
side-by-side          1.94 m


Geometry for 4 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.

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Geometry for 4 mm elements     

"Ready to saw and drill" data for mounting elements through boom with BC according SM5BSZ's BC.exe:
Note: with through Boom BC it is important to stick to the boom end offsets given below!

This table is only valid for:
Boom shape: square
Boom dim: 25 x 25 mm
Wall thickn.: 2.0 mm
Holes in boom: 6.0 mm
Offset rear: 40 mm
Offset front: 40 mm

Note: This includes a "Segmentation Density Correction" (SBC) of 1.10 mm plus an offset of 0.70 mm per element = 1.80 mm.
for compensation of the insulators shown with the GTV 70-19m website. Note: Other insulators will need other offset,
with their length being probably the most important parameter for this. Thus I advise to cut other plastic insulators
to 7 mm each to match at least the length of the pilot insulators.

Read abt. the SBC here .

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

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 1.10 mm,
total length to add is ~ 12.10 mm

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

Sketch of Bent Dipole

Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz


SWR and Return Loss plots - simulated with 4nec2

GTV 70-30 with Folded Dipole

The straight split bent dipole can be replaced with a bent folded dipole like in any non-bent Yagi design.
In doing so the transformation ratio of 1:4 remains. The bent folded dipole versions impedance is 200 ohms.

The folded dipole itself is of Ø 8 mm; I recommend an 'elements through boom' built.
So that the folded dipole is centered in the element plane for best symmetry in the elevation pattern.
For building with elements on boom see second sketch.

Geometry of the Folded Dipole

In the model we use the center of the tube, regardless of its actual diameter.

For builds ...

• ... with elements mounted through boom (Folded Dipole in element plane) use these dimensions

• ... with 8 mm elements mounted on 25 x 25 mm boom use these dimensions

Attention: Refl, DE, D1 shall be mounted on an inserted piece of 20x20 mm boom, D1 is modified.
D1 : Position: 156.5, length 311.5 + 7.5 mm of BC + 1.1 mm of SBC = D1 : 320.1 mm


EZNEC file of this Yagi with 4 mm elements 


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               1.89 m
E-plane               1.94 m

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

TANT screenshot of this Yagi with 4 mm elements

Gain vs. isotr. Rad.  25.54 dBi
Gain vs. Dipole       23.39 dBD
-3 dB H-plane, appr.  -.- deg.
-3 dB E-plane, appr.  -.- deg.
F/B                   -.- dB
F/R                   -.- dB
T_ant                 29.3 K*
G/T                  10.87 dB*

TANT screenshot of this Yagi with 8 mm elements

Gain vs. isotr. Rad.  25.59 dBi
Gain vs. Dipole       23.44 dBD
-3 dB H-plane, appr.  10.0 deg.
-3 dB E-plane, appr.  10.0 deg.
F/B                   33.6 dB
F/R                   32.8 dB
T_ant                 26.0 K*
G/T                  11.43 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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