DG7YBN - GTV 2-8w

DG7YBN / 144 MHz / GTV 2-8w Last Update Last Update July 30th 2022

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Performance Data and Geometry

Pattern and VSWR

Download as File

Crossyagi - xpol configuration

with Folded Dipole

Stacking

GTV 2-8w Yagi with bent Driven Element

Wide-band version ... a "unconditionally stable" yet high G/T Yagi that shows least
degradation with wet elements or snow on and thus easy to reproduce parameters.

Yagis generally show a degradation in performance with wet elements. Which is due to
water film or drops hanging on the elements. Thus they appear thicker when wet. Which detunes
the Yagi both in gain and pattern as in SWR. The GTV 2-8w shows very little degradation for
its G/T. If you are looking for a Yagi suitable for worst weather condx ... this one might be it.

GTV2-8w and GTV23-34w at ZS6CR

3 x vertical GTV 2-8w by OM3KSI,
Amateur Radio Club of Faculty of Aeronautics, Technical University in Kosice

• 7th place in IARU VHF ctest Low Power Multi-Operator class with this stack.

• Details: Dipole shape (flat aluminium bar 12 x 4 mm), hydraulic clamps (Stauff), no extra BC

Photo Credit: Peter, OM8WG. Tnx Peter!

GTV 2-8w xpol built by Peter, DJ4TC

Coaxes fed from rear, with the 1/4 wl lines out rearwards
Return Loss and Z on the h-plane
Return Loss and Z on the v-plane

GTV 2-8w built by Xu Da, BG5TOX

Photo credit: BG5TOX, tnx Da!

GTV 2-8w xpol built by Toralf, DJ8MS

Toralf reports the Yagi being quieter than his former Flexa Yagi and significantly quieter than a 9 ele. XPOL by M2.

GTV 2-8w xpol built by Thomas, M0ABA
Coaxes fed from rear, with the 1/4 wl lines out rearwards
... and some achievement in FT8 with the Yagi that low in the yard and approx. 40 W at feed

GTV 2-8w xpol built by Peter, DJ4TC
coaxes fed from rear, rebuilt to route the 1/4 wl lines out rearwards which results in clearer VSWR

Return Loss plots of both planes with Yagi elevated by 30 degrees

GTV 2-8w by Peter, DL1RPL

→ Place mouse over images to enlarge

GTV 2-8w by Peter, DL1RPL and VNA plot on low pole; Geometry per table 2

Philippe, F4GRT built a GTV 2-8w self modified to 145 MHz with polarisation rotator

See the mechanism in action:

Drive and pivot: click to enlarge

GTV 2-8w modified for FM Radio built by Hossein Khamooshi
Frequency modified GTV 2-8w (102-106 MHz) built by Hossein Khamooshi from the city of Gorgan, Iran for FM reception.
Boom and element holders are made from a wooden lace. Below: comparing against a 5 element design

This medium length Yagi is anchored around 144.3 MHz to produce guaranted G/T at a moderate
T_ant from 144.0 to 145.0 MHz. The bent DE (K6STI style) transforms from low impedance to 50 ohms
at feed point for direct feed.

An easy to reproduce Cross Yagi:
2 x or 4 x GTV2-8wx will do for even EME expeditions which may benefit from the Yagis stability if
mounted on a short mast with the reflectors only a few feet above ground.

Wet weather degradation analysis by courtesy of UR5EAZ: 1). G/T DRY (40.8 deg x 46.6 deg; 2.98m x 2.63m; DielC=1; Thk=0mm). Results of Tant: 233.9K; 3.6K; 234.6K; -4.45dB 2). G/T WET Degradation: (2.98m x 2.63m; DielC=8; Thk=0,1mm). Results of Tant: 233.3K; 4.0K; 234.3K; -4.4dB (!) - Very good stab.[ility] of the antenna! - Very good pattern! - Good VSWR. Владимир UR5EAZ.

Performance Data

Elem. 8 mm Gain vs. isotr. Rad. 13.4 dBi Gain vs. Dipole 11.2 dBD -3 dB H-plane 40.8 deg. -3 dB E-plane 46.6 deg. F/B -27.8 dB F/R -22.8 dB Impedance 50 ohms VSWR Band Width 1.12:1 * Mechan. Length 3696 mm Electr. Length 1.78 λ Stacking Dist. h-pol. top-to-bottom 2.63 m side-by-side 2.98 m *) as in VE7BQH G/T table = at 145.00 MHz

Geometry

4 mm elements - without BC, SBC added Refl. DE D1 D2 D3 D4 D5 D6 Pos. 0 275 431 819 1466 2198 2984 3696 Lgth. 1030.2 992.2 973.6 953.8 930.2 914.6 898.0 868.2 4 mm elements insulated through boom BC: Use SM5BSZ BC numbers and nylon rivets on square boom as shown on BC-page 3/16 in or 4.763 mm elements, 1/2 in DE - without BC, SBC added Refl. DE D1 D2 D3 D4 D5 D6 Pos. 0 275 431 819 1466 2198 2984 3696 Lgth. 1028.2 988.2 970.6 950.2 925.7 909.6 892.7 862.2 8 mm Elemente - without BC, but with SBC of 3.2 mm Refl. DE D1 D2 D3 D4 D5 D6 Pos. 0 275 431 819 1466 2198 2984 3696 Länge 1023.2 989.2 958.2 937.2 910.2 893.2 875.2 845.2 8 mm elements - on 20 x 20 mm boom with suitable BC and SBC Refl. DE D1 D2 D3 D4 D5 D6 Pos. 0 275 431 819 1466 2198 2984 3696 Lgth. 1027.1 993.1 962.1 941.1 914.1 897.1 879.1 849.1 Applies to all diameters SegmentationBC = +3.2 mm = (144.9 MHz - 144.35 MHz) * 5.85 mm/MHz BaseBC (20x20) = +3.9 mm for semi-insulated on boom Total = +7.1 mm Note: element lengths for Ø 8 mm fit 5/16" too
The Drivers diameter is 10 mm for all examples. Use EZNEC's Auto-Segmentation at 380 MHz.

Sketch of Driver Cell

Note: The tips of the bent dipole in many cases have to be brought more straigth, towards D1, by up to approx. 20 ... 30 mm.
Connect the Yagi to a VNA or SWR meter and adjust bending angle for best Return Loss.

• Bent DE Online Calculator as web app

This Yagi with 4 mm elements through a 20 x 20 x 2 mm boom

Ele. 4.0 mm
DE 10.0 mm
Boom 20 x 20 x 2 mm

"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: 1 x 1 in
Wall thickn.: 0.063 in = 1.6 mm
Holes in boom: 7.8 mm
Offset rear: 40 mm
Offset front: 40 mm

Includes an SBC of 3.22 mm

This Yagi in Imperial Measures with 3/16 in elements through a 1 x 1 in boom

Ele. 3/16 in
DE 1/2 in
Boom 1 x 1 x 0.063 in

"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: 1 x 1 in
Wall thickn.: 0.063 in = 1.6 mm
Holes in boom: 7.8 mm
Offset rear: 40 mm
Offset front: 40 mm

Includes an SBC of 3.22 mm

This Yagi with 8 mm elements on a 20 x 20 mm boom with standard insulators

Ele. 8.0 mm
DE 10 mm
Boom 20 x 20 mm

"Ready to saw and drill" data for mounting elements on boom with BC according DG7YBN for standard insulators as sold by Konni, Nuxcom, WiMo, 7arrays:

Includes an SBC of 3.22 mm

This Yagi with 8 mm elements on a 25 x 25 mm boom with high insulators by 7arrays.com

Ele. 8.0 mm
DE 10 mm
Boom 25 x 25 mm

"Ready to saw and drill" data for mounting elements on boom with BC according DG7YBN for type "insulator high 25 x 25 mm" by 7arrays:

Includes an SBC of 3.22 mm

Pattern and VSWR Plots

Elevation and Azimuth plot at 144.1 MHz

RL and SWR plot - simulated / 144 - 145 Mhz

RL and SWR plot - simulated / 140 - 150 Mhz

Gain, F/B and F/R plot - simulated

Downloads

EZNEC file of this Yagi with 4 mm elements

EZNEC file of this Yagi with 8 mm elements

EZNEC file of this Yagi as xpol with 8 mm elements on boom 25 x 25 mm

EZNEC file of the 4 Yagi Bay

An array of 8 x GTV 2-8wx for tropo and EME

Cross Yagi / X-Pol = GTV 2-8wx

on boom 25 x 25 mm: offset of element plane from centre is:

25 mm x 0.5 = 12.5 mm
plastic insulator clearance is 1.7 mm
half element diameter = position of wire in NEC = 8 mm x 0.5 = 4 mm
=> total offset = 12.5 + 1.7 + 4 = 18.2 mm => simulation carried out with 20 mm

on boom offset: second (vertical plane) = -80 mm

Performance Data


Gain vs. isotr. Rad.  13.36 dBi
Gain vs. Dipole       11.2 dBD
-3 dB H-plane         43.6 deg.
-3 dB E-plane         43.6 deg.
F/B                  -27.8 dB
F/R                  -25.5 dB
Impedance               50 ohms
VSWR Band Width     1.11:1 *
Mechan. Length        3776 mm

Stacking Dist.
top-to-bottom         2.80 m
side-by-side          2.80 m

*) as in VE7BQH G/T table = at 145.00 MHz

Pattern plot	SWR plane 1	and SWR plane 2

Imperial Measures XPOL Yagi with rear boom offset for rear feed

Ele. 3/16 in
DE 1/2 in
Boom 1 x 1 x 0.125 in

"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: 1 x 1 in
Wall thickn.: 0.125 in = 3.2 mm
Holes in boom: 7.8 mm
Offset rear: 430 resp. 510 mm
Offset front: 40 mm

Includes an SBC of 3.22 mm

This Yagi with 8 mm elements on a 25 x 25 mm boom with standard insulators

Ele. 8.0 mm
DE 10 mm
Boom 25 x 25 mm

"Ready to saw and drill" data for XPOL Yagi - mounting 8 mm elements on 25 x 25 mm boom with insulators as sold by Konni, Nuxcom, WiMo, 7arrays using DG7YBN BC:

Includes an SBC of 3.22 mm

This Yagi with 8 mm elements on a 20 x 20 mm boom with standard insulators

Ele. 8.0 mm
DE 10 mm
Boom 20 x 20 mm

"Ready to saw and drill" data for XPOL Yagi - mounting 8 mm elements on 20 x 20 mm boom with insulators as sold by Konni, Nuxcom, WiMo, 7arrays using DG7YBN BC:
With a boom 20 x 20 mm one should think about using guy ropes to add strength to the boom against shag and wind force.

Includes an SBC of 3.22 mm

This array is 7.50 x 2.50 m in summed up stacking distances. Gain = 21.8 dBi ex. phasing lines

This Yagi with a bent 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 6 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.

4nec2 Geometry Editor showing the Folded Dipole in Element Plane

Geometry of the Folded Dipole

In the model we use the center of the tube, regardless of its actual diameter.
With this height is 64 mm, span width is 980 mm. Adding the real diameter of 10 mm we end up with

inner height = 54 mm, outer span width = 990 mm, see sketch

Note: Folded Dipole mounting in plastic brackets compensation

Whatever plastic block is used to suspend or mount the dipoles wires will need to be compensated
by adding ~ 0.1 mm per millimeter of wire running in plastic. If you attach a 20 mm plastic block on top
of the boom to lead the dipoles upper wire a length of 2.0 mm / 2 = 1.0 mm needs to be added to the dipoles
span width. Assumed it runs free of contact to plastic on the down side.
We use factor 1/2 in a folded dipole then since it is a full wave loop.

Attenzione! If symmetrical to element plane this folded dipole replaces a straight dipole with out any change to D1.
However if not in element plane by means of an offset of elements by mounting on boom on insulators D1
must be adapted.

VSWR and Return Loss with a Folded Dipole in Element Plane

Stacking


Stacking Dist.    DL6WU Formula
H-plane               2.630 m
E-plane               2.984 m

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

TANT screenshot


Gain vs. isotr. Rad.  19.3 dBi
Gain vs. Dipole       17.1 dBD
-3 dB H-plane         18.2 deg.
-3 dB E-plane         21.0 deg.
F/B                  -30.5 dB
F/R                  -28.9 dB
T_los                  3.4 K
T_ant                234.6 K*
G/T                  -4.45 dB*

Theoretical numbers, no phasing line losses
nor imperfections caused by H-frame included
*) T_sky = 200 K, T_earth = 1000 K as in VE7BQH G/T table

73, Hartmut, DG7YBN